Cosmetic updates to comments and README files

configs/sama5d3-xplained/README.txt

@@ -58,7 +58,7 @@ Contents
   - NXFLAT Toolchain
   - Loading Code into SRAM with J-Link
   - Writing to FLASH using SAM-BA
-  - Running NuttX from NAND FLASH
+  - Running NuttX from SDRAM
   - Buttons and LEDs
   - Serial Console
   - Networking
@@ -324,21 +324,45 @@ Writing to FLASH using SAM-BA
        re-open the terminal emulator program.
     10. Power cycle the board.
 
-Running NuttX from NAND FLASH
+Running NuttX from SDRAM
-=============================
+========================
 
+  NuttX may be executed from SDRAM.  But this case means that the NuttX
+  binary must reside on some other media (typically NAND FLASH, Serial
+  FLASH, or, perhaps even a TFTP server).  In these cases, an intermediate
+  bootloader such as U-Boot or Barebox must be used to configure the
+  SAMA5D3 clocks and SDRAM and then to copy the NuttX binary into SDRAM.
+
+    - NuttX Configuration
     - Boot sequence
     - NAND FLASH Memory Map
     - Programming the AT91Boostrap Binary
     - Programming U-Boot
     - Load NuttX with U-Boot on AT91 boards
 
+NuttX Configuration
+-------------------
+
+  In order to run from SDRAM, NuttX must be built at origin 0x20008000 in
+  SDRAM (skipping over SDRAM memory used by the bootloader).  The following
+  configuration option is required:
+
+    CONFIG_SAMA5_BOOT_SDRAM=y
+    CONFIG_BOOT_RUNFROMSDRAM=y
+
+  These options tell the NuttX code that it will be booting and running from
+  SDRAM.  In this case, the start-logic will do to things:  (1) it will not
+  configure the SAMA5D3 clocking.  Rather, it will use the clock configuration
+  as set up by the bootloader.  And (2) it will not attempt to configure the
+  SDRAM.  Since NuttX is already running from SDRAM, it must accept the SDRAM
+  configuration as set up by the bootloader.
+
 Boot sequence
 -------------
 
   Reference: http://www.at91.com/linux4sam/bin/view/Linux4SAM/GettingStarted
 
-  Several pieces of software are involved to boot a Nutt5X from NAND.  First
+  Several pieces of software are involved to boot a Nutt5X into SDRAM.  First
   is the primary bootloader in ROM which is in charge to check if a valid
   application is present on supported media (NOR FLASH, Serial DataFlash,
   NAND FLASH, SD card).
@@ -1350,7 +1374,7 @@ SDRAM Support
 
     System Type->External Memory Configuration
       CONFIG_SAMA5_DDRCS=y                  : Tell the system that DRAM is at the DDR CS
-      CONFIG_SAMA5_DDRCS_SIZE=268435456     : 2Gb DRAM -> 256GB
+      CONFIG_SAMA5_DDRCS_SIZE=268435456     : 2Gb DRAM -> 256MB
       CONFIG_SAMA5_DDRCS_LPDDR2=y           : Its DDR2
       CONFIG_SAMA5D3XPLAINED_MT47H128M16RT=y          : This is the type of DDR2
 

configs/sama5d3-xplained/src/sam_sdram.c

@@ -4,7 +4,7 @@
  *   Copyright (C) 2014 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
- * Most of this file derives from Atmel sample code for the SAMA5D3x-E
+ * Most of this file derives from Atmel sample code for the SAMA5D3 Xplained
  * board.  That sample code has licensing that is compatible with the NuttX
  * modified BSD license:
  *
@@ -122,14 +122,13 @@ static inline void sam_sdram_delay(unsigned int loops)
  * Name: sam_sdram_config
  *
  * Description:
- *   Configures DDR2 (MT47H128M16RT 128MB/ MT47H64M16HR)
- *
  *   Configures DDR2 (MT47H128M16RT 128MB or, optionally,  MT47H64M16HR)
  *
- *   Per the SAMA5D3-Xplained User guide: "Two SDRAM/DDR2 used as main system memory.
+ *   Per the SAMA5D3-Xplained User guide: "Two DDR2/SDRAM (MT47H64M16HR) used as
- *   MT47H128M16 - 2 Gb - 16 Meg x 16 x 8 banks, the board provides up to 2 Gb on-
+ *   main system memory (256 MByte). The board includes 2 Gbits of on-board soldered
- *   board, soldered DDR2 SDRAM. The memory bus is 32 bits wide and operates with
+ *   DDR2 (double data rate) SDRAM. The footprints can also host two DDR2
- *   up to 166 MHz."
+ *   (MT47H128M16RT) from Micron® for a total of 512 MBytes of DDR2 memory. The
+ *   memory bus is 32 bits wide and operates with a frequency of up to 166 MHz."
  *
  *   From the Atmel Code Example:
  *     MT47H64M16HR : 8 Meg x 16 x 8 banks

configs/sama5d3x-ek/README.txt

@@ -70,7 +70,7 @@ Contents
   - Loading Code into SRAM with J-Link
   - Writing to FLASH using SAM-BA
   - Creating and Using NORBOOT
-  - Running NuttX from NAND FLASH
+  - Running NuttX from SDRAM
   - Buttons and LEDs
   - Serial Consoles
   - Networking
@@ -445,21 +445,45 @@ Creating and Using NORBOOT
         jumper does nothing on my board???  So I have been using the norboot
         configuration exclusively to start the program-under-test in NOR FLASH.
 
-Running NuttX from NAND FLASH
+Running NuttX from SDRAM
-=============================
+========================
 
+  NuttX may be executed from SDRAM.  But this case means that the NuttX
+  binary must reside on some other media (typically NAND FLASH, Serial
+  FLASH, or, perhaps even a TFTP server).  In these cases, an intermediate
+  bootloader such as U-Boot or Barebox must be used to configure the
+  SAMA5D3 clocks and SDRAM and then to copy the NuttX binary into SDRAM.
+
+    - NuttX Configuration
     - Boot sequence
     - NAND FLASH Memory Map
     - Programming the AT91Boostrap Binary
     - Programming U-Boot
     - Load NuttX with U-Boot on AT91 boards
 
+NuttX Configuration
+-------------------
+
+  In order to run from SDRAM, NuttX must be built at origin 0x20008000 in
+  SDRAM (skipping over SDRAM memory used by the bootloader).  The following
+  configuration option is required:
+
+    CONFIG_SAMA5_BOOT_SDRAM=y
+    CONFIG_BOOT_RUNFROMSDRAM=y
+
+  These options tell the NuttX code that it will be booting and running from
+  SDRAM.  In this case, the start-logic will do to things:  (1) it will not
+  configure the SAMA5D3 clocking.  Rather, it will use the clock configuration
+  as set up by the bootloader.  And (2) it will not attempt to configure the
+  SDRAM.  Since NuttX is already running from SDRAM, it must accept the SDRAM
+  configuration as set up by the bootloader.
+
 Boot sequence
 -------------
 
   Reference: http://www.at91.com/linux4sam/bin/view/Linux4SAM/GettingStarted
 
-  Several pieces of software are involved to boot a Nutt5X from NAND.  First
+  Several pieces of software are involved to boot a Nutt5X into SDRAM.  First
   is the primary bootloader in ROM which is in charge to check if a valid
   application is present on supported media (NOR FLASH, Serial DataFlash,
   NAND FLASH, SD card).
@@ -1519,7 +1543,7 @@ SDRAM Support
 
     System Type->External Memory Configuration
       CONFIG_SAMA5_DDRCS=y                  : Tell the system that DRAM is at the DDR CS
-      CONFIG_SAMA5_DDRCS_SIZE=268435456     : 2Gb DRAM -> 256GB
+      CONFIG_SAMA5_DDRCS_SIZE=268435456     : 2Gb DRAM -> 256MB
       CONFIG_SAMA5_DDRCS_LPDDR2=y           : Its DDR2
       CONFIG_SAMA5D3xEK_MT47H128M16RT=y     : This is the type of DDR2
 

configs/sama5d3x-ek/src/sam_boot.c

@@ -80,7 +80,7 @@ void sam_boardinitialize(void)
 
 #if defined(CONFIG_SAMA5_DDRCS) && !defined(CONFIG_SAMA5_BOOT_SDRAM)
 
-  /* Configure SDRAM if (1) SDRAM has been enalbled in the NuttX configuration and
+  /* Configure SDRAM if (1) SDRAM has been enabled in the NuttX configuration and
    * (2) if we are not currently running out of SDRAM.  If we are now running out
    * of SDRAM then we have to assume that some second level bootloader has properly
    * configured SDRAM for our use.
@@ -103,7 +103,7 @@ void sam_boardinitialize(void)
     }
 #endif
 
-  /* Configure board resources to support networkingif the 1) networking is enabled,
+  /* Configure board resources to support networking if the 1) networking is enabled,
    * 2) the EMAC or GMAC module is enabled, and 2) the weak function
    * sam_netinitialize() has been brought into the build.
    */

configs/sama5d3x-ek/src/sam_sdram.c

@@ -122,8 +122,6 @@ static inline void sam_sdram_delay(unsigned int loops)
  * Name: sam_sdram_config
  *
  * Description:
- *   Configures DDR2 (MT47H128M16RT 128MB/ MT47H64M16HR)
- *
  *   Configures DDR2 (MT47H128M16RT 128MB or, optionally,  MT47H64M16HR)
  *
  *   Per the SAMA5D3x-EK User guide: "Two SDRAM/DDR2 used as main system memory.