atmel-samd: Introduce a nvm module for non-volatile byte-level memory access. (#203)

* atmel-samd: Introduce a nvm module for non-volatile byte-level memory access.

This allows for persisting small configuration values even when the file system
is read-only from CircuitPython.

Fixes #160

* Review feedback:
* Add tests.
* Fix non-zero index.
* Fix len()

14 files changed, 35 insertions, 10 deletions

diff --git a/atmel-samd/boards/arduino_zero/mpconfigboard.h b/atmel-samd/boards/arduino_zero/mpconfigboard.h
index dd4ec88d3..149963840 100644
--- a/atmel-samd/boards/arduino_zero/mpconfigboard.h
+++ b/atmel-samd/boards/arduino_zero/mpconfigboard.h
@@ -12,4 +12,6 @@
 
 #include "internal_flash.h"
 
+#define CIRCUITPY_INTERNAL_NVM_SIZE 0
+
 #define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - 0x010000)
diff --git a/atmel-samd/boards/circuitplayground_express/mpconfigboard.h b/atmel-samd/boards/circuitplayground_express/mpconfigboard.h
index 9499d25a2..f9ff05084 100644
--- a/atmel-samd/boards/circuitplayground_express/mpconfigboard.h
+++ b/atmel-samd/boards/circuitplayground_express/mpconfigboard.h
@@ -25,7 +25,11 @@
 
 #include "spi_flash.h"
 
-#define BOARD_FLASH_SIZE (0x00040000 - 0x2000)
+// If you change this, then make sure to update the linker scripts as well to
+// make sure you don't overwrite code.
+#define CIRCUITPY_INTERNAL_NVM_SIZE 256
+
+#define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - CIRCUITPY_INTERNAL_NVM_SIZE)
 
 #include "flash_S25FL216K.h"
 #include "flash_GD25Q16C.h"
diff --git a/atmel-samd/boards/feather_m0_adalogger/mpconfigboard.h b/atmel-samd/boards/feather_m0_adalogger/mpconfigboard.h
index f1b9dfcbe..2a2d21dd3 100644
--- a/atmel-samd/boards/feather_m0_adalogger/mpconfigboard.h
+++ b/atmel-samd/boards/feather_m0_adalogger/mpconfigboard.h
@@ -11,4 +11,6 @@
 
 #include "internal_flash.h"
 
+#define CIRCUITPY_INTERNAL_NVM_SIZE 0
+
 #define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - 0x010000)
diff --git a/atmel-samd/boards/feather_m0_basic/mpconfigboard.h b/atmel-samd/boards/feather_m0_basic/mpconfigboard.h
index ff6088c3a..a8a8247fa 100644
--- a/atmel-samd/boards/feather_m0_basic/mpconfigboard.h
+++ b/atmel-samd/boards/feather_m0_basic/mpconfigboard.h
@@ -11,4 +11,6 @@
 
 #include "internal_flash.h"
 
+#define CIRCUITPY_INTERNAL_NVM_SIZE 0
+
 #define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - 0x010000)
diff --git a/atmel-samd/boards/feather_m0_express/mpconfigboard.h b/atmel-samd/boards/feather_m0_express/mpconfigboard.h
index 929a8c0f3..896a04dd8 100644
--- a/atmel-samd/boards/feather_m0_express/mpconfigboard.h
+++ b/atmel-samd/boards/feather_m0_express/mpconfigboard.h
@@ -23,7 +23,11 @@
 
 #include "spi_flash.h"
 
-#define BOARD_FLASH_SIZE (0x00040000 - 0x2000)
+// If you change this, then make sure to update the linker scripts as well to
+// make sure you don't overwrite code.
+#define CIRCUITPY_INTERNAL_NVM_SIZE 256
+
+#define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - CIRCUITPY_INTERNAL_NVM_SIZE)
 
 #include "flash_S25FL216K.h"
 #include "flash_GD25Q16C.h"
diff --git a/atmel-samd/boards/gemma_m0/mpconfigboard.h b/atmel-samd/boards/gemma_m0/mpconfigboard.h
index ae1aa24a1..8988c9a63 100644
--- a/atmel-samd/boards/gemma_m0/mpconfigboard.h
+++ b/atmel-samd/boards/gemma_m0/mpconfigboard.h
@@ -11,6 +11,8 @@
 #define MICROPY_PORT_A        (PORT_PA00 | PORT_PA01 | PORT_PA24 | PORT_PA25)
 #define MICROPY_PORT_B        (0)
 
+#define CIRCUITPY_INTERNAL_NVM_SIZE 0
+
 #include "internal_flash.h"
 
 #define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - 0x010000)
diff --git a/atmel-samd/boards/metro_m0_express/mpconfigboard.h b/atmel-samd/boards/metro_m0_express/mpconfigboard.h
index 9bb9a2f79..cbc28dc78 100644
--- a/atmel-samd/boards/metro_m0_express/mpconfigboard.h
+++ b/atmel-samd/boards/metro_m0_express/mpconfigboard.h
@@ -25,7 +25,11 @@
 
 #include "spi_flash.h"
 
-#define BOARD_FLASH_SIZE (0x00040000 - 0x2000)
+// If you change this, then make sure to update the linker scripts as well to
+// make sure you don't overwrite code.
+#define CIRCUITPY_INTERNAL_NVM_SIZE 256
+
+#define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - CIRCUITPY_INTERNAL_NVM_SIZE)
 
 #include "flash_S25FL216K.h"
 #include "flash_GD25Q16C.h"
diff --git a/atmel-samd/boards/samd21x18-bootloader-crystalless.ld b/atmel-samd/boards/samd21x18-bootloader-crystalless.ld
index 96527ab7e..56ae5feb4 100644
--- a/atmel-samd/boards/samd21x18-bootloader-crystalless.ld
+++ b/atmel-samd/boards/samd21x18-bootloader-crystalless.ld
@@ -5,8 +5,8 @@
 /* Specify the memory areas */
 MEMORY
 {
-    /* Leave 8KiB for the bootloader, 256b for persistent config (clock), and 64k for the flash file system. */
-    FLASH (rx) : ORIGIN = 0x00000000+0x2000, LENGTH = 0x00040000 - 0x2000 - 0x100 - 0x010000
+    /* Leave 8KiB for the bootloader, 256b for persistent config (clock), 64k for the flash file system and 256b for the user config. */
+    FLASH (rx) : ORIGIN = 0x00000000+0x2000, LENGTH = 0x00040000 - 0x2000 - 0x100 - 0x010000 - 0x100
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x008000 /* 32 KiB */
 }
 
diff --git a/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld b/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld
index a6be02f90..1c0424747 100644
--- a/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld
+++ b/atmel-samd/boards/samd21x18-bootloader-external-flash-crystalless.ld
@@ -5,7 +5,8 @@
 /* Specify the memory areas */
 MEMORY
 {
-    FLASH (rx) : ORIGIN = 0x00000000 + 0x2000, LENGTH = 0x00040000 - 0x2000 - 0x100 /* Leave 8KiB for the bootloader and 256b for config. */
+    /* Leave 8KiB for the bootloader, 256b for internal config and 256b for user config. */
+    FLASH (rx) : ORIGIN = 0x00000000 + 0x2000, LENGTH = 0x00040000 - 0x2000 - 0x100 - 0x100
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x008000 /* 32 KiB */
 }
 
diff --git a/atmel-samd/boards/samd21x18-bootloader-external-flash.ld b/atmel-samd/boards/samd21x18-bootloader-external-flash.ld
index bb1d3fdc4..4346c170c 100644
--- a/atmel-samd/boards/samd21x18-bootloader-external-flash.ld
+++ b/atmel-samd/boards/samd21x18-bootloader-external-flash.ld
@@ -5,7 +5,7 @@
 /* Specify the memory areas */
 MEMORY
 {
-    FLASH (rx) : ORIGIN = 0x00000000 + 0x2000, LENGTH = 0x00040000 - 0x2000 /* Leave 8KiB for the bootloader. */
+    FLASH (rx) : ORIGIN = 0x00000000 + 0x2000, LENGTH = 0x00040000 - 0x2000 - 0x100 /* Leave 8KiB for the bootloader and 256b for user config. */
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x008000 /* 32 KiB */
 }
 
diff --git a/atmel-samd/boards/samd21x18-bootloader.ld b/atmel-samd/boards/samd21x18-bootloader.ld
index 0ea475ede..13a3f75c1 100644
--- a/atmel-samd/boards/samd21x18-bootloader.ld
+++ b/atmel-samd/boards/samd21x18-bootloader.ld
@@ -5,7 +5,7 @@
 /* Specify the memory areas */
 MEMORY
 {
-    /* Leave 8KiB for the bootloader and 64k for the flash file system. */
+    /* Leave 8KiB for the bootloader, and 64k for the flash file system. */
     FLASH (rx) : ORIGIN = 0x00000000+0x2000, LENGTH = 0x00040000 - 0x2000 - 0x010000
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x008000 /* 32 KiB */
 }
diff --git a/atmel-samd/boards/samd21x18-external-flash.ld b/atmel-samd/boards/samd21x18-external-flash.ld
index 90cb6160a..f5797cf6f 100644
--- a/atmel-samd/boards/samd21x18-external-flash.ld
+++ b/atmel-samd/boards/samd21x18-external-flash.ld
@@ -5,7 +5,8 @@
 /* Specify the memory areas */
 MEMORY
 {
-    FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 0x00040000 - 0x100 /* 256 KiB but leave 256b for config */
+    /* 256 KiB but leave 256b for internal config and 256b for user config (protected eeprom) */
+    FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 0x00040000 - 0x100 - 0x100
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x008000 /* 32 KiB */
 }
 
diff --git a/atmel-samd/boards/samd21x18.ld b/atmel-samd/boards/samd21x18.ld
index 98a24a811..a68094758 100644
--- a/atmel-samd/boards/samd21x18.ld
+++ b/atmel-samd/boards/samd21x18.ld
@@ -5,7 +5,8 @@
 /* Specify the memory areas */
 MEMORY
 {
-    FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 0x00040000 - 0x100 - 0x010000 /* Leave 256b for config and 64k for the flash file system. */
+    /* Leave 256b for internal config, 64k for the flash file system and 256b for user config. */
+    FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 0x00040000 - 0x100 - 0x010000
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x008000 /* 32 KiB */
 }
 
diff --git a/atmel-samd/boards/trinket_m0/mpconfigboard.h b/atmel-samd/boards/trinket_m0/mpconfigboard.h
index 7bb4f14cf..8fc70f22d 100644
--- a/atmel-samd/boards/trinket_m0/mpconfigboard.h
+++ b/atmel-samd/boards/trinket_m0/mpconfigboard.h
@@ -12,4 +12,6 @@
 
 #include "internal_flash.h"
 
+#define CIRCUITPY_INTERNAL_NVM_SIZE 0
+
 #define BOARD_FLASH_SIZE (0x00040000 - 0x2000 - 0x010000)