SAMV71-XULT: Add support for an external I2C RTC

configs/same70-xplained/README.txt

@@ -35,6 +35,10 @@ address 0x00000000, but trying to step through with AtmelStudio 7 results
 in uninterpretble behavior.  Using the Segger J-Link, I get errors trying
 to reset and halt the board so I am unable to use that debugger either.
 
+WARNING:  This README derives heavily from the SAMV71-XULT README file and
+may still contain some logic that pertains only to that board.  This is a
+work in progress
+
 See also configs/samv71-xult/README.txt
 
 Serial Console

configs/samv71-xult/src/sam_bringup.c

@@ -70,6 +70,13 @@
 #  include "sam_progmem.h"
 #endif
 
+#ifdef HAVE_RTC_DSXXXX
+#  include <nuttx/clock.h>
+#  include <nuttx/i2c.h>
+#  include <nuttx/timers/ds3231.h>
+#  include "sam_twihs.h"
+#endif
+
 #ifdef HAVE_ROMFS
 #  include <arch/board/boot_romfsimg.h>
 #endif
@@ -110,12 +117,42 @@ int sam_bringup(void)
 #if defined(HAVE_S25FL1) || defined(HAVE_PROGMEM_CHARDEV)
   FAR struct mtd_dev_s *mtd;
 #endif
+#ifdef HAVE_RTC_DSXXXX
+  FAR struct i2c_dev_s *i2c;
+#endif
 #if defined(HAVE_S25FL1_CHARDEV) || defined(HAVE_PROGMEM_CHARDEV)
   char blockdev[18];
   char chardev[12];
 #endif
   int ret;
 
+#ifdef HAVE_RTC_DSXXXX
+  /* Get an instance of the TWIHS0 I2C interface */
+
+  i2c = up_i2cinitialize(DSXXXX_TWI_BUS);
+  if (i2c == NULL)
+    {
+      SYSLOG("ERROR: up_i2cinitialize(%d) failed\n", DSXXXX_TWI_BUS);
+    }
+  else
+    {
+      /* Use the I2C interface to initialize the DSXXXX timer */
+
+      ret = dsxxxx_rtc_initialize(i2c);
+      if (ret < 0)
+        {
+          SYSLOG("ERROR: dsxxxx_rtc_initialize() failed: %d\n", ret);
+        }
+      else
+        {
+          /* Synchronize the system time to the RTC time */
+
+          clock_synchronize();
+        }
+    }
+
+#endif
+
 #ifdef HAVE_MACADDR
   /* Read the Ethernet MAC address from the AT24 FLASH and configure the
    * Ethernet driver with that address.

configs/samv71-xult/src/samv71-xult.h

@@ -68,6 +68,7 @@
 #define HAVE_PROGMEM_CHARDEV 1
 #define HAVE_WM8904          1
 #define HAVE_AUDIO_NULL      1
+#define HAVE_RTC_DSXXXX      1
 
 /* HSMCI */
 /* Can't support MMC/SD if the card interface is not enabled */
@@ -298,6 +299,27 @@
 #  endif
 #endif
 
+/* DS3231/DS1307 RTC
+ *
+ * For testing purposes, I have connected a Maximum Integrated I2C RTC TWIHS0
+ * (available on either EXT or EXT2 pins 11 and 12).
+ */
+
+#if !defined(CONFIG_SAMV7_TWIHS0) || !defined(CONFIG_RTC_DSXXXX)
+#  undef HAVE_RTC_DSXXXX
+#endif
+
+#if !defined(CONFIG_RTC) || !defined(CONFIG_RTC_DATETIME)
+#  undef HAVE_RTC_DSXXXX
+#endif
+
+#ifdef HAVE_RTC_DSXXXX
+/* The DS3231/1307 RTC communicates on TWI0, I2C address 0x68 */
+
+#  define DSXXXX_TWI_BUS     0
+#  define DSXXXX_I2C_ADDRESS 0x68
+#endif
+
 /* SAMV71-XULT GPIO Pin Definitions *************************************************/
 
 /* Ethernet MAC.