README
^^^^^^

  This README discusses issues unique to NuttX configurations for the
  Arduino DUE board featuring the Atmel ATSAM3X8E MCU running at 84
  MHz.

  Supported Shields
  -----------------
  - ITEAD 2.4" TFT with Touch, Arduion Shield 1.0

Contents
^^^^^^^^

  - PIO Pin Usage
  - ITEAD 2.4" TFT with Touch
  - Development Environment
  - GNU Toolchain Options
  - IDEs
  - NuttX EABI "buildroot" Toolchain
  - NuttX OABI "buildroot" Toolchain
  - NXFLAT Toolchain
  - Buttons and LEDs
  - Serial Consoles
  - Loading Code
  - SAM4S Xplained-specific Configuration Options
  - Configurations

PIO Pin Usage
^^^^^^^^^^^^^

  PORTA                          PORTB                          PORTC
  ------------------------------ ------------------------------ --------------------------------
  PIO   SIGNAL     CONN PIN      PIO   SIGNAL       CONN PIN    PIO   SIGNAL      CONN PIN
  ----- ---------- ---- -------- ----- ------------ ---- ------ ----- ----------- ---- ---------
  PA0   CANTX0     ADCH 8        PB0   ETX_CLK      ETH  1      PC0   ERASE       N/A
  PA1   CANRX0     ACDH 7        PB1   ETX_EN       ETH  3      PC1   PIN33       XIO  14
  PA2   AD7        ADCL 8        PB2   ETXD0        ETH  5      PC2   PIN34       XIO  15
  PA3   AD6        ADCL 7        PB3   ETXD1        ETH  7      PC3   PIN35       XIO  16
  PA4   AD5        ADCL 6        PB4   ERX_DV       ETH  10     PC4   PIN36       XIO  17
  PA5   EEXTINT    ETH  8        PB5   ERXD0        ETH  9      PC5   PIN37       XIO  18
  PA6   AD4        ADCL 5        PB6   ERXD1        ETH  11     PC6   PIN38       XIO  19
  PA7   PIN31      XIO  12       PB7   ERX_ER       ETH  13     PC7   PIN39       XIO  20
  PA8   [U]RX      PWML 1        PB8   EMDC         ETH  14     PC8   PIN40       XIO  21
  PA9   [U]TX      PWML 2        PB9   EMDIO        ETH  12     PC9   PIN41       XIO  22
  PA10  RXD2       COMM 6        PB10  UOTGVBOF     Vbus power  PC10  N/C         N/A
  PA11  TXD2       COMM 5        PB11  UOTGID       USB1 4      PC11  N/C         N/A
  PA12  RXD1       COMM 4        PB12  SDA0-3       COMM 7      PC12  PIN51       XIO  32
  PA13  TXD1       COMM 3        PB13  SCL0-3       COMM 8      PC13  PIN50       XIO  31
  PA14  PIN23      XIO  4        PB14  CANTX1/IO    XIO  34     PC14  PIN49       XIO  30
  PA15  PIN24      XIO  5        PB15  DAC0(CANRX1) ADCH 5      PC15  PIN48       XIO  29
  PA16  AD0        ADCL 1        PB16  DAC1         ADCH 6      PC16  PIN47       XIO  28
  PA17  SDA1       PWMH 9        PB17  AD8          ADCH 1      PC17  PIN46       XIO  27
  PA18  SCL1       PWMH 10       PB18  AD9          ADCH 2      PC18  PIN45       XIO  26
  PA19  PIN42      XIO  23       PB19  AD10         ADCH 3      PC19  PIN44       XIO  25
  PA20  PIN43      XIO  24       PB20  AD11(TXD3)   ADCH 4      PC20  N/C         N/A
  PA21  TXL        TX YELLOW LED PB21  AD14(RXD3)   XIO  33     PC21  PWM9        PWMH 2
  PA22  AD3        ADCL 4        PB22  N/C          N/A         PC22  PWM8        PWMH 1
  PA23  AD2        ADCL 3        PB23  SS3          ???         PC23  PWM7        PWML 8
  PA24  AD1        ADCL 2        PB24  N/C          N/A         PC24  PWM6        PWML 7
  PA25  MISO       SPI  1        PB25  PWM2         PWML 3      PC25  PWM5        PWML 6
  PA26  MOSI       SPI  4        PB26  PIN22        ???         PC26  SS1/PWM4    PWML 10 (there are two)
  PA27  SPCK       SPI  3        PB27  PWM13        PWMH 6      PC27  N/C         N/A
  PA28  SS0/PWM10  (ETH) PWML 10 PB28  JTAG_TCK     JTAG 4      PC28  PWM3        PWML 4
  PA29  SS1/PWM4   (SD)          PB29  JTAG_TDI     JTAG 8      PC29  SS0/PWM10   ??? (there are two)
  PA30  N/A         N/A          PB30  JTAG_TDO     JTAG 6      PC30  RXL         RX YELLOW LED
  PA31  N/A         N/A          PB31  JTAG_TMS     JTAG 2      PC31  N/A         N/A
  ----- ---------- ---- -------- ----- ------------ ---- ------ ----- ----------- ---- ---------

  PORTA                          PORTB                          PORTC
  ------------------------------ ------------------------------ --------------------------------
  PIO   SIGNAL     CONN PIN      PIO   SIGNAL       CONN PIN    PIO   SIGNAL      CONN PIN
  ----- ---------- ---- -------- ----- ------------ ---- ------ ----- ----------- ---- ---------
  PA0   PIN25       XIO  6       PE0   N/A          N/A         PF0   N/A         N/A
  PD1   PIN26       XIO  7       PE1   N/A          N/A         PF1   N/A         N/A
  PD2   PIN27       XIO  8       PE2   N/A          N/A         PF2   N/A         N/A
  PD3   PIN28       XIO  9       PE3   N/A          N/A         PF3   N/A         N/A
  PD4   TXD0        COMM 1       PE4   N/A          N/A         PF4   N/A         N/A
  PD5   RXD0        COMM 2       PE5   N/A          N/A         PF5   N/A         N/A
  PD6   PIN29       XIO  10      PE6   N/A          N/A         PF6   N/A         N/A
  PD7   PWM11       PWMH 4       PE7   N/A          N/A         PF7   N/A         N/A
  PD8   PWM12       PWMH 5       PE8   N/A          N/A         PF8   N/A         N/A
  PD9   PIN30       XIO  11      PE9   N/A          N/A         PF9   N/A         N/A
  PD10  PIN32       XIO  13      PE10  N/A          N/A         PF10  N/A         N/A
  PD11  N/A         N/A          PE11  N/A          N/A         PF11  N/A         N/A
  PD12  N/A         N/A          PE12  N/A          N/A         PF12  N/A         N/A
  PD13  N/A         N/A          PE13  N/A          N/A         PF13  N/A         N/A
  PD14  N/A         N/A          PE14  N/A          N/A         PF14  N/A         N/A
  PD15  N/A         N/A          PE15  N/A          N/A         PF15  N/A         N/A
  PD16  N/A         N/A          PE16  N/A          N/A         PF16  N/A         N/A
  PD17  N/A         N/A          PE17  N/A          N/A         PF17  N/A         N/A
  PD18  N/A         N/A          PE18  N/A          N/A         PF18  N/A         N/A
  PD19  N/A         N/A          PE19  N/A          N/A         PF19  N/A         N/A
  PD20  N/A         N/A          PE20  N/A          N/A         PF20  N/A         N/A
  PD21  N/A         N/A          PE21  N/A          N/A         PF21  N/A         N/A
  PD22  N/A         N/A          PE22  N/A          N/A         PF22  N/A         N/A
  PD23  N/A         N/A          PE23  N/A          N/A         PF23  N/A         N/A
  PD24  N/A         N/A          PE24  N/A          N/A         PF24  N/A         N/A
  PD25  N/A         N/A          PE25  N/A          N/A         PF25  N/A         N/A
  PD26  N/A         N/A          PE26  N/A          N/A         PF26  N/A         N/A
  PD27  N/A         N/A          PE27  N/A          N/A         PF27  N/A         N/A
  PD28  N/A         N/A          PE28  N/A          N/A         PF28  N/A         N/A
  PD29  N/A         N/A          PE29  N/A          N/A         PF29  N/A         N/A
  PD30  N/A         N/A          PE30  N/A          N/A         PF30  N/A         N/A
  PD31  N/A5        N/A          PE31  N/A          N/A         PF31  N/A         N/A
  ----- ---------- ---- -------- ----- ------------ ---- ------ ----- ----------- ---- ---------

ITEAD 2.4" TFT with Touch
^^^^^^^^^^^^^^^^^^^^^^^^^

  The Arduino 2.4" TFT Touch Shield is designed for all the Arduino
  compatible boards. It works in 3.3V voltage level. It can be directly
  plugged on the Arduino and other compatible boards. It will offer
  display, touch and storage functions for the Arduino board

  Features:

    1. Compatible with 3.3/5V operation voltage level
    2. Compatible with UTFT library
    3. With SD Card Socket

  The Arduino 2.4" TFT Touch shield uses the S6D1121 controller , it
  supports 8-bit data interface. The touch IC is XPT2046.

  NOTE:  When used with the ITEAD shield, the power from the USB connector
  seems to be inefficient (for example, I lose the USB connection when I
  insert an SD card).  I recommends using a 7-12V power supply with the
  Arduino in this case.

  Connector:

  ---------- --------------------------- ----------- --------------------------- ------------------
  Arduino            ATSAM3X                 Due             ITHEAD
  Due PIN    GPIO FUNCTION               SIGNAL      PIN              SIGNAL     NOTES
  ---------- ---- ---------------------- ----------- ---------------- ---------- ------------------
  PWMH
  10  SCL1   PA18 TWCK0/A20/WKUP9        SCL1         ---      ---    ---        SCL not available
   9  SDA1   PA17 TWD0SPCK0              SDA1         ---      ---    ---        SDA not available
   8  Aref   ---  ---                    AREF         J2 pin 8 Vref   N/C        ---
   7  GND    ---  ---                    GND          J2 pin 7 GND    ---        ---
   6  PWM13  PB27 SPI0_SPCK/A20/WKUP10   PWM13        J2 pin 6 D13    SD_SCK     SCK, also LED "L", Pulled low
   5  PWM12  PD8  A21/NANDALE/TIOB8      PWM12        J2 pin 5 D12    SD_MISO    MISO not available
   4  PWM11  PD7  A17/BA1/TIOA8          PWM11        J2 pin 4 D11    SD_MOSI    MOSI not available, Pulled low
   3  PWM10  PA28 SPI0_NPCS0/PCK2/WKUP11 SS0/PWM10    J2 pin 3 D10    SD_CS      Pulled low on-board
   2  PWM9   PC21 A0/NBS0/PWML4          PWM9         J2 pin 2 D9     Touch_Dout ---
   1  PWM8   PC22 A1/PWML5               PWM8         J2 pin 1 D8     Touch_IRQ  ---

  PWML
   8  PWM7   PC23 A2/PWML6               PWM7         J3 pin 8 D7     DB15       ---
   7  PWM6   PC24 A3/PWML7               PWM6         J3 pin 7 D6     DB14       ---
   6  PWM5   PC25 A4/TIOA6               PWM5         J3 pin 6 D5     DB13       ---
   5  PWM4   PC26 A5/TIOB6               SS1/PWM4     J3 pin 5 D4     DB12       ---
   4  PWM3   PC28 A7/TIOA7               PWM3         J3 pin 4 D3     DB11       ---
   3  PWM2   PB25 RTS0/TIOA0             PWM2         J3 pin 3 D2     DB10       ---
   2  PWM1   PA9  UTXD/PWMH3             TX           J3 pin 2 D1     DB9        UART0 TX
   1  PWM0   PA8  URXD/PWMH0/WKUP4       RX           J3 pin 1 D0     DB8        UART0 RX
  ---------- ---- ---------------------- ----------- ---------------- ---------- ------------------
  POWER
   1  ---    ---  ---                    ---          ---      ---    ---        ---
   2  IOref  ---  ---                    IOREF +3V3   ---      ---    ---        ---
   3  RESET  ---  ---                    MASTER_RESET J4 pin 1 RST    ---        ---
   5  5V     ---  ---                    +5V          J4 pin 2 3.3V   ---        ---
   4  3.3V   ---  ---                    +3V3         J4 pin 3 5V     ---        ---
   6  GND    ---  ---                    GND          J4 pin 4 GND    ---        ---
   7  GND    ---  ---                    GND          J4 pin 5 GND    ---        ---
   8  Vin    ---  ---                    VIN          J4 pin 6 Vin    ---        ---
  ADCL
   1  A0     PA16 SPCK1/TD/AD7           AD0          J1 pin 1 A0/D14 Touch_Din  ---
   2  A1     PA24 MCDA3/PCK1/AD6         AD1          J1 pin 2 A1/D15 Touch_CLK  ---
   3  A2     PA23 MCDA2/TCLK4/AD5        AD2          J1 pin 3 A2/D16 ---        ---
   4  A3     PA22 MCDA1/TCLK3/AD4        AD3          J1 pin 4 A3/D17 TFT_CS     ---
   5  A4     PA6  TIOB2/NCS0/AD3         AD4          J1 pin 5 A4/D18 TFT_WR     ---
   6  A5     PA4  TCLK1/NWAIT/AD2        AD5          J1 pin 6 A5/D19 TFT_RS     ---
   7  A6     PA3  TIOB1/PWMFI1/AD1/WKUP1 AD6          ---      ---    ---        ---
   8  A7     PA2  TIOA1/NANDRDY/AD0      AD7          ---      ---    ---        ---
  ---------- ---- ---------------------- ----------- ---------------- ---------- ------------------

  NOTES:

  1. It is not possible to use any of the SPI devices on the Shield unless
     a bit-bang SPI interface is used.  This includes the touch controller
     a bit-bang SPI interface is used.  This includes the touch controller
     and the SD card.
  2. UART0 cannot be used.  USARTs on the COMM connector should be available.
  3. Parallel data is not contiguous in the PIO register
  4. Touchcontroller /CS pin is connected to ground (always selected).
  5. Either PA28 or PC29 may drive PWM10
  6. The schematics I have do not agree with the documentation.  The Touch IRQ
     and Dout pins are reversed in the Documentation (D9 an D8, respectively).
     I am assuming that the schematic is correct (and the schematic does seem
     to match up with what little I can see on the single visible side of the
     board).

  SD Interface:

  ------------ ------------------ ------- ------------- ------------------ -------
  SD CONNECTOR ARDUINO CONNECTORS AT91SAM SD CONNECTOR  ARDUINO CONNECTORS AT91SAM
  PIN SIGNAL   PIN      SIGNAL    GPIO    PIN  SIGNAL   PIN      SIGNAL    GPIO
  --- -------- -------- --------- -------- ---- -------- -------- --------- -------
   1  /CS      J2 pin 3 D10       PA28     2    DI       J2 pin 4 D11       PD7
   3  GND      ---      ---       ---      4    VCC      ---      ---       ---
   5  CLK      J2 pin 6 D13       PB27     6    GND      ---      ---       ---
   7  DO       J2 pin 5 D12       PD8      8    IRQ      N/C      ---       ---
   9  N/C      ---      ---       ---      10   SW       N/C      ---       ---
   11 WP       N/C      ---       ---      12   CD       N/C      ---       ---
   13 CD       N/C      ---       ---      14   GND      ---      ---       ---
   15 GND      ---      ---       ---      16   GND      ---      ---       ---
  --- -------- -------- --------- -------- ---- -------- -------- --------- -------

  NOTES:
  -  The SD slot shares the pin with LED "L" so LED support must be disabled to
     use the MMC/SD card on the ITEAD shield.
  - Either PA28 or PC29 may drive D10

  Touch Controller Interface:

  ----------- ------------------ -------- ------------- ------------------ -------
    XPT2046   ARDUINO CONNECTORS AT91SAM   XPT2046     ARDUINO CONNECTORS AT91SAM
  PIN SIGNAL  PIN      SIGNAL    GPIO     PIN  SIGNAL   PIN      SIGNAL    GPIO
  --- ------- -------- --------- -------- ---- -------- -------- --------- -------
   1  VCC     ---      ---       ---      2    X+       ---      ---       ---
   3  Y+      ---      ---       ---      4    X-       ---      ---       ---
   5  Y-      ---      ---       ---      6    GND      ---      ---       ---
   7  IN3     N/C      ---       ---      8    IN4      N/C      ---       ---
   9  VREF    ---      ---       ---      10   VCC      ---      ---       ---
   11 IRQ     J2 pin 2 D9        PC21     12   DOUT     J2 pin 1 D8        PC22
   13 BUSY    N/C      ---       ---      14   DIN      J1 pin 1 A0/D15    PA16
   15 /CS     ---      ---       ---      16   DCLK     J1 pin 2 A1/D15    PA24
  --- ------- -------- --------- -------- ---- -------- -------- --------- -------

  NOTES:
  - /CS is connected to ground (XPT2046 is always selected)

Development Environment
^^^^^^^^^^^^^^^^^^^^^^^

  Either Linux or Cygwin on Windows can be used for the development environment.
  The source has been built only using the GNU toolchain (see below).  Other
  toolchains will likely cause problems. Testing was performed using the Cygwin
  environment.

GNU Toolchain Options
^^^^^^^^^^^^^^^^^^^^^

  The NuttX make system has been modified to support the following different
  toolchain options.

  1. The CodeSourcery GNU toolchain,
  2. The devkitARM GNU toolchain, ok
  4. The NuttX buildroot Toolchain (see below).

  All testing has been conducted using the NuttX buildroot toolchain.  However,
  the make system is setup to default to use the devkitARM toolchain.  To use
  the CodeSourcery, devkitARM or Raisonance GNU toolchain, you simply need to
  add one of the following configuration options to your .config (or defconfig)
  file:

    CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y  : CodeSourcery under Windows
    CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYL=y  : CodeSourcery under Linux
    CONFIG_ARMV7M_TOOLCHAIN_ATOLLIC=y        : Atollic toolchain for Windos
    CONFIG_ARMV7M_TOOLCHAIN_DEVKITARM=y      : devkitARM under Windows
    CONFIG_ARMV7M_TOOLCHAIN_BUILDROOT=y      : NuttX buildroot under Linux or Cygwin (default)
    CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIL=y      : Generic GCC ARM EABI toolchain for Linux
    CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIW=y      : Generic GCC ARM EABI toolchain for Windows

  If you are not using CONFIG_ARMV7M_TOOLCHAIN_BUILDROOT, then you may also
  have to modify the PATH in the setenv.h file if your make cannot find the
  tools.

  NOTE about Windows native toolchains
  ------------------------------------

  The CodeSourcery (for Windows), Atollic, and devkitARM toolchains are
  Windows native toolchains.  The CodeSourcery (for Linux), NuttX buildroot,
  and, perhaps, the generic GCC toolchains are Cygwin and/or Linux native
  toolchains. There are several limitations to using a Windows based
  toolchain in a Cygwin environment.  The three biggest are:

  1. The Windows toolchain cannot follow Cygwin paths.  Path conversions are
     performed automatically in the Cygwin makefiles using the 'cygpath' utility
     but you might easily find some new path problems.  If so, check out 'cygpath -w'

  2. Windows toolchains cannot follow Cygwin symbolic links.  Many symbolic links
     are used in Nuttx (e.g., include/arch).  The make system works around these
     problems for the Windows tools by copying directories instead of linking them.
     But this can also cause some confusion for you:  For example, you may edit
     a file in a "linked" directory and find that your changes had no effect.
     That is because you are building the copy of the file in the "fake" symbolic
     directory.  If you use a Windows toolchain, you should get in the habit of
     making like this:

       make clean_context all

     An alias in your .bashrc file might make that less painful.

  3. Dependencies are not made when using Windows versions of the GCC.  This is
     because the dependencies are generated using Windows pathes which do not
     work with the Cygwin make.

       MKDEP                = $(TOPDIR)/tools/mknulldeps.sh

  NOTE 1: The CodeSourcery toolchain (2009q1) does not work with default optimization
  level of -Os (See Make.defs).  It will work with -O0, -O1, or -O2, but not with
  -Os.

  NOTE 2: The devkitARM toolchain includes a version of MSYS make.  Make sure that
  the paths to Cygwin's /bin and /usr/bin directories appear BEFORE the devkitARM
  path or will get the wrong version of make.

IDEs
^^^^

  NuttX is built using command-line make.  It can be used with an IDE, but some
  effort will be required to create the project (There is a simple RIDE project
  in the RIDE subdirectory).

  Makefile Build
  --------------
  Under Eclipse, it is pretty easy to set up an "empty makefile project" and
  simply use the NuttX makefile to build the system.  That is almost for free
  under Linux.  Under Windows, you will need to set up the "Cygwin GCC" empty
  makefile project in order to work with Windows (Google for "Eclipse Cygwin" -
  there is a lot of help on the internet).

  Native Build
  ------------
  Here are a few tips before you start that effort:

  1) Select the toolchain that you will be using in your .config file
  2) Start the NuttX build at least one time from the Cygwin command line
     before trying to create your project.  This is necessary to create
     certain auto-generated files and directories that will be needed.
  3) Set up include pathes:  You will need include/, arch/arm/src/sam34,
     arch/arm/src/common, arch/arm/src/armv7-m, and sched/.
  4) All assembly files need to have the definition option -D __ASSEMBLY__
     on the command line.

  Startup files will probably cause you some headaches.  The NuttX startup file
  is arch/arm/src/sam34/sam_vectors.S.  You may need to build NuttX
  one time from the Cygwin command line in order to obtain the pre-built
  startup object needed by RIDE.

NuttX EABI "buildroot" Toolchain
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  A GNU GCC-based toolchain is assumed.  The files */setenv.sh should
  be modified to point to the correct path to the Cortex-M3 GCC toolchain (if
  different from the default in your PATH variable).

  If you have no Cortex-M3 toolchain, one can be downloaded from the NuttX
  SourceForge download site (https://sourceforge.net/projects/nuttx/files/buildroot/).
  This GNU toolchain builds and executes in the Linux or Cygwin environment.

  1. You must have already configured Nuttx in <some-dir>/nuttx.

     cd tools
     ./configure.shsam4s-xplained/<sub-dir>

  2. Download the latest buildroot package into <some-dir>

  3. unpack the buildroot tarball.  The resulting directory may
     have versioning information on it like buildroot-x.y.z.  If so,
     rename <some-dir>/buildroot-x.y.z to <some-dir>/buildroot.

  4. cd <some-dir>/buildroot

  5. cp configs/cortexm3-eabi-defconfig-4.6.3 .config

  6. make oldconfig

  7. make

  8. Edit setenv.h, if necessary, so that the PATH variable includes
     the path to the newly built binaries.

  See the file configs/README.txt in the buildroot source tree.  That has more
  details PLUS some special instructions that you will need to follow if you are
  building a Cortex-M3 toolchain for Cygwin under Windows.

  NOTE:  Unfortunately, the 4.6.3 EABI toolchain is not compatible with the
  the NXFLAT tools.  See the top-level TODO file (under "Binary loaders") for
  more information about this problem. If you plan to use NXFLAT, please do not
  use the GCC 4.6.3 EABI toochain; instead use the GCC 4.3.3 OABI toolchain.
  See instructions below.

NuttX OABI "buildroot" Toolchain
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  The older, OABI buildroot toolchain is also available.  To use the OABI
  toolchain:

  1. When building the buildroot toolchain, either (1) modify the cortexm3-eabi-defconfig-4.6.3
     configuration to use EABI (using 'make menuconfig'), or (2) use an exising OABI
     configuration such as cortexm3-defconfig-4.3.3

  2. Modify the Make.defs file to use the OABI conventions:

    +CROSSDEV = arm-nuttx-elf-
    +ARCHCPUFLAGS = -mtune=cortex-m3 -march=armv7-m -mfloat-abi=soft
    +NXFLATLDFLAGS2 = $(NXFLATLDFLAGS1) -T$(TOPDIR)/binfmt/libnxflat/gnu-nxflat-gotoff.ld -no-check-sections
    -CROSSDEV = arm-nuttx-eabi-
    -ARCHCPUFLAGS = -mcpu=cortex-m3 -mthumb -mfloat-abi=soft
    -NXFLATLDFLAGS2 = $(NXFLATLDFLAGS1) -T$(TOPDIR)/binfmt/libnxflat/gnu-nxflat-pcrel.ld -no-check-sections

NXFLAT Toolchain
^^^^^^^^^^^^^^^^

  If you are *not* using the NuttX buildroot toolchain and you want to use
  the NXFLAT tools, then you will still have to build a portion of the buildroot
  tools -- just the NXFLAT tools.  The buildroot with the NXFLAT tools can
  be downloaded from the NuttX SourceForge download site
  (https://sourceforge.net/projects/nuttx/files/).

  This GNU toolchain builds and executes in the Linux or Cygwin environment.

  1. You must have already configured Nuttx in <some-dir>/nuttx.

     cd tools
     ./configure.sh lpcxpresso-lpc1768/<sub-dir>

  2. Download the latest buildroot package into <some-dir>

  3. unpack the buildroot tarball.  The resulting directory may
     have versioning information on it like buildroot-x.y.z.  If so,
     rename <some-dir>/buildroot-x.y.z to <some-dir>/buildroot.

  4. cd <some-dir>/buildroot

  5. cp configs/cortexm3-defconfig-nxflat .config

  6. make oldconfig

  7. make

  8. Edit setenv.h, if necessary, so that the PATH variable includes
     the path to the newly builtNXFLAT binaries.

Buttons and LEDs
^^^^^^^^^^^^^^^^

  Buttons
  -------
  There are no buttons on the Arduino Due board.

  LEDs
  ----
  There are three user-controllable LEDs on board the Arduino Due board:

      LED              GPIO
      ---------------- -----
      L   Amber LED    PB27
      TX  Yellow LED   PA21
      RX  Yellow LED   PC30

  LED L is connected to ground and can be illuminated by driving the PB27
  output high. The TX and RX LEDs are pulled high and can be illuminated by
  driving the corresponding
  GPIO output to low.

  These LEDs are not used by the board port unless CONFIG_ARCH_LEDS is
  defined.  In that case, the usage by the board port is defined in
  include/board.h and src/sam_leds.c. The LEDs are used to encode OS-related
  events as follows:

    SYMBOL                MEANING                         LED STATE
                                                    L         TX       RX
    -------------------  -----------------------  -------- -------- --------
    LED_STARTED          NuttX has been started     OFF      OFF      OFF
    LED_HEAPALLOCATE     Heap has been allocated    OFF      OFF      OFF
    LED_IRQSENABLED      Interrupts enabled         OFF      OFF      OFF
    LED_STACKCREATED     Idle stack created         ON       OFF      OFF
    LED_INIRQ            In an interrupt            N/C      GLOW     OFF
    LED_SIGNAL           In a signal handler        N/C      GLOW     OFF
    LED_ASSERTION        An assertion failed        N/C      GLOW     OFF
    LED_PANIC            The system has crashed     N/C      N/C      Blinking
    LED_IDLE             MCU is is sleep mode       ------ Not used --------

  Thus if LED L is statically on, NuttX has successfully booted and is,
  apparently, running normmally.  If LED RX is glowing, then NuttX is
  handling interupts (and also signals and assertions).  If TX is flashing
  at approximately 2Hz, then a fatal error has been detected and the system
  has halted.

Serial Consoles
^^^^^^^^^^^^^^^

  The SAM3X has a UART and 4 USARTS.  The Programming port uses a USB-to-
  serial chip connected to the first UART0 of the MCU (RX0 and TX0).  The
  output from that port is visible using the Arduino tool.

  Any of UART and USART0-3 may be used as a serial console.  By default,
  the UART is used as the serial console in all configurations.  But that is
  easily changed by modifying the configuration as described under
  "Configurations" below.

  Here are the UART signals available on pins.  Under signal name, the first
  column is the name on the schematic associated with the GPIO, the second
  comes from: http://arduino.cc/en/Hacking/PinMappingSAM3X, and the third
  is the name of the multiplexed SAM3X UART function from the data sheet.
  This is more than a little confusing.

    ------------------------------------------------------------------
    PIO              SIGNAL NAME                    CONNECTOR PIN
          DUE SCHEM. PIN MAPPING    SAM3X       DUE SCHEM. BOARD LABEL
    ----- ---------- -------------- ----------- ---------- -----------
    PA8   [U]RX      RX0            UART0  URXD  PWML 1    RX0<-0
    PA9   [U]TX      TX0            UART0  UTXD  PWML 2    TX0->1
    PD5   RXD0       RX3            USART3 RXD3  COMM 2    RX3
    PD4   TXD0       TX3            USART3 TXD3  COMM 1    TX3
    PA12  RXD1       RX2            USART1 RXD1  COMM 4    TX2
    PA13  TXD1       TX2            USART1 TXD1  COMM 3    RX2
    PA10  RXD2       RX1            USART0 RXD0  COMM 6    RX1
    PA11  TXD2       TX1            USART0 TXD0  COMM 5    TX1
    PB21  AD14(RXD3) Digital Pin 52 USART2 RXD2  XIO  33   33
    PB20  AD11(TXD3) Analog In 11   USART2 TXD2  ADCH 4    A11

  The outputs from these pins is 3.3V.  You will need to connect RS232
  transceiver to get the signals to RS232 levels (or connect to the
  USB virual COM port in the case of UART0).

Loading Code
^^^^^^^^^^^^

  Installing the Arduino USB Driver under Windows:
  ------------------------------------------------
  1.  Download the Windows version of the Arduino software, not the 1.0.x
      release but the latest 1.5.x that supports the Due. When the download
      finishes, unzip the downloaded file.
  2. Connect the Due to your computer with a USB cable via the Programming port.
  3. The Windows driver installation should fail.
  4. Open the Device Manger
  5. Look for the listing named "Ports (COM & LPT)". You should see an open
     port named "Arduino Due Prog. Port".
  6 Select the "Browse my computer for Driver software" option.
  7. Right click on the "Arduino Due Prog. Port" and choose "Update Driver
     Software".
  8. Navigate to the folder with the Arduino IDE you downloaded and unzipped
     earlier. Locate and select the "Drivers" folder in the main Arduino folder
     (not the "FTDI USB Drivers" sub-directory).

  Uploading NuttX to the Due Using Bossa:
  ---------------------------------------
  I don't think this can be done because the Arduino software is so dedicated
  to "sketches".  However, Arduino uses BOSSA under the hood to load code and
  you can use BOSSA outside of Arduino.

  Uploading NuttX to the Due Using Bossa:
  ---------------------------------------
  Where do you get it?
    Generic BOSSA installation files are avaialable here:
    http://sourceforge.net/projects/b-o-s-s-a/?source=dlp

    However, DUE uses a patched version of BOSSA available as source code here:
    https://github.com/shumatech/BOSSA/tree/arduino

    But, fortunately, since you already installed Arduino, you already have
    BOSSA installed.  In my installation, it is here:

    C:\Program Files (x86)\Arduino\arduino-1.5.2\hardware\tools\bossac.exe

  General Procedure
  -----------------

    1) Erase the FLASH and put the Due in bootloader mode
    2) Write the file to FLASH
    3) Configure to boot from FLASH
    4) Reset the DUE

  Erase FLASH and Put the Due in Bootloader Mode
  ----------------------------------------------
    This is accomplished by simply configuring the programming port in 1200
    baud and sending something on the programming port.  Here is some sample
    output from a Windows CMD.exe shell.  NOTE that my Arduino programming
    port shows up as COM26.  It may be different on yoursystem.

    To enter boot mode, set the baud to 1200 and send anything to the
    programming port:

      C:\Program Files (x86)\Arduino\arduino-1.5.2\hardware\tools>mode com26:1200,n,8,1

      Status for device COM26:
      ------------------------
          Baud:            1200
          Parity:          None
          Data Bits:       8
          Stop Bits:       1
          Timeout:         ON
          XON/XOFF:        OFF
          CTS handshaking: OFF
          DSR handshaking: OFF
          DSR sensitivity: OFF
          DTR circuit:     ON
          RTS circuit:     ON

      C:\Program Files (x86)\Arduino\arduino-1.5.2\hardware\tools>bossac.exe --port=COM26 -U false -i
      Device       : ATSAM3X8
      Chip ID      : 285e0a60
      Version      : v1.1 Dec 15 2010 19:25:04
      Address      : 524288
      Pages        : 2048
      Page Size    : 256 bytes
      Total Size   : 512KB
      Planes       : 2
      Lock Regions : 32
      Locked       : none
      Security     : false
      Boot Flash   : false

  Writing FLASH and Setting FLASH Boot Mode
  -----------------------------------------
    In a Cygwin BaSH shell:

      export PATH="/cygdrive/c/Program Files (x86)/Arduino/arduino-1.5.2/hardware/tools":$PATH

    Erasing, writing, and verifying FLASH with bossac:

      $ bossac.exe --port=COM26 -U false -e -w -v -b nuttx.bin -R
      Erase flash
      Write 86588 bytes to flash
      [==============================] 100% (339/339 pages)
      Verify 86588 bytes of flash
      [==============================] 100% (339/339 pages)
      Verify successful
      Set boot flash true
      CPU reset.

    Some things that can go wrong:

      $ bossac.exe --port=COM26 -U false -e -w -v -b nuttx.bin -R
      No device found on COM26

    This error means that there is code running on the Due already so the
    bootloader cannot connect. Pressing reset and trying again

      $ bossac.exe --port=COM26 -U false -e -w -v -b nuttx.bin -R
      No device found on COM26

    Sill No connection because Duo does not jump to bootloader after reset.
    Press ERASE button and try again

      $ bossac.exe --port=COM26 -U false -e -w -v -b nuttx.bin -R
      Erase flash
      Write 86588 bytes to flash
      [==============================] 100% (339/339 pages)
      Verify 86588 bytes of flash
      [==============================] 100% (339/339 pages)
      Verify successful
      Set boot flash true
      CPU reset.

  Other useful bossac things operations.
  -------------------------------------
    a) Write code to FLASH don't change boot mode and don't reset.  This lets
       you examine the FLASH contents that you just loaded while the bootloader
       is still active.

       $ bossac.exe --port=COM26 -U false -e -w -v --boot=0 nuttx.bin
       Write 64628 bytes to flash
       [==============================] 100% (253/253 pages)
       Verify 64628 bytes of flash
       [==============================] 100% (253/253 pages)
       Verify successful

    b) Verify the FLASH contents (the bootloader must be running)

       $ bossac.exe --port=COM26 -U false -v nuttx.bin
       Verify 64628 bytes of flash
       [==============================] 100% (253/253 pages)
       Verify successful

    c) Read from FLASH to a file  (the bootloader must be running):

       $ bossac.exe --port=COM26 -U false --read=4096 nuttx.dump
       Read 4096 bytes from flash
       [==============================] 100% (16/16 pages)

    d) Change to boot from FLASH

       $ bossac.exe --port=COM26 -U false --boot=1
       Set boot flash true

  Uploading NuttX to the Due Using JTAG:
  -------------------------------------

  The JTAG/SWD signals are brought out to a 10-pin header JTAG connector:

    PIN SIGNAL         JTAG STANDARD     NOTES
    --- -------------- ----------------- --------------------------------
     1  3.3V           VTref
     2  JTAG_TMS       SWDIO/TMS         SAM3X pin 31, Pulled up on board
     3  GND            GND
     4  JTAG_TCK       SWDCLK/TCK        SAM3X pin 28, Pulled up on board
     5  GND            GND
     6  JTAG_TDO       SWO/EXta/TRACECTL SAM3X pin 30, ulled up on board
     7  N/C            Key
     8  JTAG_TDI       NC/EXTb/TDI       SAM3X pin 29, Pulled up on board
     9  GND            GNDDetect
     10 MASTER-RESET   nReset

   You should be able to use a 10- to 20-pin adaptr to connect a SAM-ICE
   debugger to the Arduino Due.  I have this Olimex adapter:
   https://www.olimex.com/Products/ARM/JTAG/ARM-JTAG-20-10/ . But so far I
   have been unable to get the get the SAM-ICE to communicate with the Due.

Arduino DUE-specific Configuration Options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  CONFIG_ARCH - Identifies the arch/ subdirectory.  This should
  be set to:

    CONFIG_ARCH=arm

  CONFIG_ARCH_family - For use in C code:

    CONFIG_ARCH_ARM=y

  CONFIG_ARCH_architecture - For use in C code:

    CONFIG_ARCH_CORTEXM3=y

  CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory

    CONFIG_ARCH_CHIP="sam34"

  CONFIG_ARCH_CHIP_name - For use in C code to identify the exact
  chip:

    CONFIG_ARCH_CHIP_SAM34
    CONFIG_ARCH_CHIP_SAM3X
    CONFIG_ARCH_CHIP_ATSAM3X8E

  CONFIG_ARCH_BOARD - Identifies the configs subdirectory and
  hence, the board that supports the particular chip or SoC.

    CONFIG_ARCH_BOARD=arduino-due (for the Arduino Due development board)

  CONFIG_ARCH_BOARD_name - For use in C code

    CONFIG_ARCH_BOARD_ARDUINO_DUE=y

  CONFIG_ARCH_LOOPSPERMSEC - Must be calibrated for correct operation
  of delay loops

  CONFIG_ENDIAN_BIG - define if big endian (default is little
  endian)

  CONFIG_RAM_SIZE - Describes the installed DRAM (SRAM in this case):

    CONFIG_RAM_SIZE=0x00008000 (32Kb)

  CONFIG_RAM_START - The start address of installed DRAM

    CONFIG_RAM_START=0x20000000

  CONFIG_ARCH_IRQPRIO - The SAM3UF103Z supports interrupt prioritization

    CONFIG_ARCH_IRQPRIO=y

  CONFIG_ARCH_LEDS - Use LEDs to show state. Unique to boards that
  have LEDs

  CONFIG_ARCH_INTERRUPTSTACK - This architecture supports an interrupt
  stack. If defined, this symbol is the size of the interrupt
  stack in bytes.  If not defined, the user task stacks will be
  used during interrupt handling.

  CONFIG_ARCH_STACKDUMP - Do stack dumps after assertions

  CONFIG_ARCH_LEDS -  Use LEDs to show state. Unique to board architecture.

  CONFIG_ARCH_CALIBRATION - Enables some build in instrumentation that
  cause a 100 second delay during boot-up.  This 100 second delay
  serves no purpose other than it allows you to calibratre
  CONFIG_ARCH_LOOPSPERMSEC.  You simply use a stop watch to measure
  the 100 second delay then adjust CONFIG_ARCH_LOOPSPERMSEC until
  the delay actually is 100 seconds.

  Individual subsystems can be enabled:

    CONFIG_SAM34_RTC         - Real Time Clock
    CONFIG_SAM34_RTT         - Real Time Timer
    CONFIG_SAM34_WDT         - Watchdog Timer
    CONFIG_SAM34_UART0       - UART 0
    CONFIG_SAM34_SMC         - Static Memory Controller
    CONFIG_SAM34_SDRAMC      - SDRAM Controller
    CONFIG_SAM34_USART0      - USART 0
    CONFIG_SAM34_USART1      - USART 1
    CONFIG_SAM34_USART2      - USART 2
    CONFIG_SAM34_USART3      - USART 3
    CONFIG_SAM34_HSMCI       - High Speed Multimedia Card Interface
    CONFIG_SAM34_TWI0        - Two-Wire Interface 0 (master/slave)
    CONFIG_SAM34_TWI1        - Two-Wire Interface 1 (master/slave)
    CONFIG_SAM34_SPI0        - Serial Peripheral Interface 0
    CONFIG_SAM34_SPI1        - Serial Peripheral Interface 1
    CONFIG_SAM34_SSC         - Synchronous Serial Controller
    CONFIG_SAM34_TC0         - Timer Counter 0
    CONFIG_SAM34_TC1         - Timer Counter 1
    CONFIG_SAM34_TC2         - Timer Counter 2
    CONFIG_SAM34_TC3         - Timer Counter 3
    CONFIG_SAM34_TC4         - Timer Counter 4
    CONFIG_SAM34_TC5         - Timer Counter 5
    CONFIG_SAM34_TC6         - Timer Counter 6
    CONFIG_SAM34_TC7         - Timer Counter 7
    CONFIG_SAM34_TC8         - Timer Counter 8
    CONFIG_SAM34_PWM         - Pulse Width Modulation
    CONFIG_SAM34_ADC12B      - 12-bit Analog To Digital Converter
    CONFIG_SAM34_DACC        - Digital To Analog Converter
    CONFIG_SAM34_DMA         - DMA Controller
    CONFIG_SAM34_UOTGHS      - USB OTG High Speed
    CONFIG_SAM34_TRNG        - True Random Number Generator
    CONFIG_SAM34_EMAC        - Ethernet MAC
    CONFIG_SAM34_CAN0        - CAN Controller 0
    CONFIG_SAM34_CAN1        - CAN Controller 1

  Some subsystems can be configured to operate in different ways. The drivers
  need to know how to configure the subsystem.

    CONFIG_GPIOA_IRQ
    CONFIG_GPIOB_IRQ
    CONFIG_GPIOC_IRQ
    CONFIG_GPIOD_IRQ
    CONFIG_GPIOE_IRQ
    CONFIG_GPIOF_IRQ
    CONFIG_USART0_ISUART
    CONFIG_USART1_ISUART
    CONFIG_USART2_ISUART
    CONFIG_USART3_ISUART

  ST91SAM4S specific device driver settings

    CONFIG_U[S]ARTn_SERIAL_CONSOLE - selects the USARTn (n=0,1,2,3) or UART
           m (m=4,5) for the console and ttys0 (default is the USART1).
    CONFIG_U[S]ARTn_RXBUFSIZE - Characters are buffered as received.
       This specific the size of the receive buffer
    CONFIG_U[S]ARTn_TXBUFSIZE - Characters are buffered before
       being sent.  This specific the size of the transmit buffer
    CONFIG_U[S]ARTn_BAUD - The configure BAUD of the UART.  Must be
    CONFIG_U[S]ARTn_BITS - The number of bits.  Must be either 7 or 8.
    CONFIG_U[S]ARTn_PARTIY - 0=no parity, 1=odd parity, 2=even parity
    CONFIG_U[S]ARTn_2STOP - Two stop bits

Configurations
^^^^^^^^^^^^^^

  Each SAM4S Xplained configuration is maintained in a sub-directory and
  can be selected as follow:

    cd tools
    ./configure.sh arduino-due/<subdir>
    cd -
    . ./setenv.sh

  Before sourcing the setenv.sh file above, you should examine it and perform
  edits as necessary so that BUILDROOT_BIN is the correct path to the directory
  than holds your toolchain binaries.

  And then build NuttX by simply typing the following.  At the conclusion of
  the make, the nuttx binary will reside in an ELF file called, simply, nuttx.

    make

  The <subdir> that is provided above as an argument to the tools/configure.sh
  must be is one of the following.

  NOTES:

  1. These configurations use the mconf-based configuration tool.  To
    change any of these configurations using that tool, you should:

    a. Build and install the kconfig-mconf tool.  See nuttx/README.txt
       and misc/tools/

    b. Execute 'make menuconfig' in nuttx/ in order to start the
       reconfiguration process.

  2. Unless stated otherwise, all configurations generate console
     output on UART0 which is available both on the USB virtual COM port
     and on the PWML connector (see the section "Serial Consoles" above).

     However, the pin usage by the ITEAD TFT shield conflict with the pin
     usage for UART0.  In this case you need to switch to USART0 by
     modifying the configuration as follows:

       Board Selection -> Peripheral
         CONFIG_SAM34_UART0=n              : Disable UART0.  Can't use with this shield
         CONFIG_SAM34_USART0=y             : Enable USART0
         CONFIG_USART0_ISUART=y

       Device Drivers -> Serial
         CONFIG_USART0_SERIAL_CONSOLE=y    : Configure the console on USART0
         CONFIG_USART0_RXBUFSIZE=256
         CONFIG_USART0_TXBUFSIZE=256
         CONFIG_USART0_BAUD=115200
         CONFIG_USART0_BITS=8
         CONFIG_USART0_PARITY=0
         CONFIG_USART0_2STOP=0

     NOTE: USART0 TTL levels are available on COMM 5 (TXD0) and COMM 6 (RXD0).

  3. Unless otherwise stated, the configurations are setup for
     Linux (or any other POSIX environment like Cygwin under Windows):

     Build Setup:
       CONFIG_HOST_LINUX=y   : Linux or other POSIX environment

  4. These configurations use the older, OABI, buildroot toolchain.  But
     that is easily reconfigured:

     System Type -> Toolchain:
       CONFIG_ARMV7M_TOOLCHAIN_BUILDROOT=y : Buildroot toolchain
       CONFIG_ARMV7M_OABI_TOOLCHAIN=y      : Older, OABI toolchain

     If you want to use the Atmel GCC toolchain, here are the steps to
     do so:

     Build Setup:
       CONFIG_HOST_WINDOWS=y   : Windows
       CONFIG_HOST_CYGWIN=y    : Using Cygwin or other POSIX environment

     System Type -> Toolchain:
       CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIW=y : General GCC EABI toolchain under windows

     This re-configuration should be done before making NuttX or else the
     subsequent 'make' will fail.  If you have already attempted building
     NuttX then you will have to 1) 'make distclean' to remove the old
     configuration, 2) 'cd tools; ./configure.sh sam3u-ek/ksnh' to start
     with a fresh configuration, and 3) perform the configuration changes
     above.

     Also, make sure that your PATH variable has the new path to your
     Atmel tools.  Try 'which arm-none-eabi-gcc' to make sure that you
     are selecting the right tool.  setenv.sh is available for you to
     use to set or PATH variable.  The path in the that file may not,
     however, be correct for your installation.

     See also the "NOTE about Windows native toolchains" in the section call
     "GNU Toolchain Options" above.

Configuration sub-directories
-----------------------------

  ostest:
    This configuration directory performs a simple OS test using
    examples/ostest.  See NOTES above.

  nsh:
    This configuration directory will built the NuttShell.  See NOTES above.

    NOTES:
    1. NSH built-in applications are supported.  However, there are
       no built-in applications built with the default configuration.

       Binary Formats:
         CONFIG_BUILTIN=y                    : Enable support for built-in programs

       Applicaton Configuration:
         CONFIG_NSH_BUILTIN_APPS=y           : Enable starting apps from NSH command line

    2. By default, this configuration uses UART0 and has support LEDs
       enabled.  UART0 output is available on the USB debugging port or
       on pins 0-1 of the PWML connector.

       This configuration can be modified to use peripherals on the ITEAD
       TFT shield as described below.  However, in that case the UART0 and
       LED "L" GPIO pins conflict with the pin usage by the ITEAD TFT
       Shield.  In this case you need to switch to USART0 and disable LEDs
       by modifying the configuration as follows:

       Board Selection -> Peripheral
         CONFIG_SAM34_UART0=n              : Disable UART0.  Can't use with this shield
         CONFIG_SAM34_USART0=y             : Enable USART0
         CONFIG_USART0_ISUART=y

       Device Drivers -> Serial
         CONFIG_USART0_SERIAL_CONSOLE=y    : Configure the console on USART0
         CONFIG_USART0_RXBUFSIZE=256
         CONFIG_USART0_TXBUFSIZE=256
         CONFIG_USART0_BAUD=115200
         CONFIG_USART0_BITS=8
         CONFIG_USART0_PARITY=0
         CONFIG_USART0_2STOP=0

         NOTE: USART0 TTL levels are available on COMM 5 (TXD0) and
         COMM 6 (RXD0)

       Board Selection -> Board-Specific Options:
         CONFIG_ARCH_LEDS=n                : Can't support LEDs with this shield installed
         CONFIG_ARDUINO_ITHEAD_TFT=y       : Enable support for the Shield

    3. If the ITEAD TFT shield is connected to the Arduino Due, then
       support for the SD card slot can be enabled by making the following
       changes to the configuration:

       NOTE: You cannot use UART0 or LEDs with this ITEAD module.  You must
       switch to USART0 and disable LED support as described above.

       Board Selection -> Board-Specific Options:
         CONFIG_ARDUINO_ITHEAD_TFT=y       : Enable support for the Shield

       File Systems:
         CONFIG_DISABLE_MOUNTPOINT=n       : Mountpoint support is needed
         CONFIG_FS_FAT=y                   : Enable the FAT file system
         CONFIG_FAT_LCNAMES=y              : Enable upper/lower case 8.3 file names (Optional, see below)
         CONFIG_FAT_LFN=y                  : Enable long file named (Optional, see below)
         CONFIG_FAT_MAXFNAME=32            : Maximum supported file name length

         There are issues related to patents that Microsoft holds on FAT long
         file name technologies.  See the top level COPYING file for further
         details.

       Device Drivers
         CONFIG_SPI=y                      : Enable SPI support
         CONFIG_SPI_EXCHANGE=y             : The exchange() method is supported
         CONFIG_SPI_OWNBUS=y               : Smaller code if this is the only SPI device
         CONFIG_SPI_BITBANG=y              : Enable SPI bit-bang support

         CONFIG_MMCSD=y                    : Enable MMC/SD support
         CONFIG_MMCSD_NSLOTS=1             : Only one MMC/SD card slot
         CONFIG_MMCSD_MULTIBLOCK_DISABLE=n : Should not need to disable multi-block transfers
         CONFIG_MMCSD_HAVECARDDETECT=y     : I/O1 module as a card detect GPIO
         CONFIG_MMCSD_SPI=y                : Use the SPI interface to the MMC/SD card
         CONFIG_MMCSD_SPICLOCK=20000000    : This is a guess for the optimal MMC/SD frequency
         CONFIG_MMCSD_SPIMODE=0            : Mode 0 is required

       Board Selection -> Common Board Options
         CONFIG_NSH_ARCHINIT=y             : Initialize the MMC/SD slot when NSH starts
         CONFIG_NSH_MMCSDSLOTNO=0          : Only one MMC/SD slot, slot 0
         CONFIG_NSH_MMCSDSPIPORTNO=0       : (does not really matter in this case)

       Application Configuration -> NSH Library
         CONFIG_NSH_ARCHINIT=y             : Board has architecture-specific initialization

       STATUS:
       2013-7-2:  SD card is not responding.  All 0's received on SPI.

    3. This configuration has been used for verifying the touchscreen on
       on the ITEAD TFT Shield.  With the modifications below, you can
       include the touchscreen test program at apps/examples/touchscreen as
       an NSH built-in application.  You can enable the touchscreen and test
       by modifying the  default configuration in the following ways:

       NOTE: You cannot use UART0 or LEDs with this ITEAD module.  You must
       switch to USART0 and disable LED support as described above.

       Board Selection -> Board-Specific Options:
         CONFIG_ARDUINO_ITHEAD_TFT=y       : Enable support for the Shield

       Device Drivers
         CONFIG_SPI=y                      : Enable SPI support
         CONFIG_SPI_EXCHANGE=y             : The exchange() method is supported
         CONFIG_SPI_OWNBUS=y               : Smaller code if this is the only SPI device
         CONFIG_SPI_BITBANG=y              : Enable SPI bit-bang support

         CONFIG_INPUT=y                    : Enable support for input devices
         CONFIG_INPUT_ADS7843E=y           : Enable support for the XPT2046
         CONFIG_ADS7843E_SPIDEV=0          : (Doesn't matter)
         CONFIG_ADS7843E_SPIMODE=0         : Use SPI mode 0
         CONFIG_ADS7843E_FREQUENCY=1000000 : SPI BAUD 1MHz
         CONFIG_ADS7843E_SWAPXY=y          : If landscpe orientation
         CONFIG_ADS7843E_THRESHX=51        : These will probably need to be tuned
         CONFIG_ADS7843E_THRESHY=39

       System Type:
         CONFIG_GPIO_IRQ=y                 : GPIO interrupt support
         CONFIG_GPIOACIRQ=y                : Enable GPIO interrupts from port C

       RTOS Features:
         CONFIG_DISABLE_SIGNALS=n          : Signals are required

       Library Support:
         CONFIG_SCHED_WORKQUEUE=y          : Work queue support required

       Applicaton Configuration:
         CONFIG_EXAMPLES_TOUCHSCREEN=y     : Enable the touchscreen built-int test

       Defaults should be okay for related touchscreen settings.  Touchscreen
       debug output on USART0 can be enabled with:

       Build Setup:
         CONFIG_DEBUG=y                    : Enable debug features
         CONFIG_DEBUG_VERBOSE=y            : Enable verbose debug output
         CONFIG_DEBUG_INPUT=y              : Enable debug output from input devices

       STATUS:
       2013-7-2:  TSC is not responding.  All 0's received on SPI.

