Update NVM_BYTEARRAY_BUFFER_LEN

ports/stm/boards/thunderpack/mpconfigboard.h

@@ -26,11 +26,18 @@
 #define MICROPY_HW_BOARD_NAME       "THUNDERPACK"
 #define MICROPY_HW_MCU_NAME         "STM32F411CE"
 
-#define FLASH_SIZE                         (0x80000)
-#define FLASH_PAGE_SIZE                    (0x4000)
+// Non-volatile memory config
 #define CIRCUITPY_INTERNAL_NVM_SIZE        (0x4000)
 #define CIRCUITPY_INTERNAL_NVM_START_ADDR  (0x0800C000)
 #define CIRCUITPY_INTERNAL_NVM_SECTOR      FLASH_SECTOR_3
+
+// Putting the entire flash sector in the NVM byte array buffer
+// would take up too much RAM. This limits how much of the sector we use.
+#define NVM_BYTEARRAY_BUFFER_LEN           512
+
+// Flash config
+#define FLASH_SIZE                         (0x80000)
+#define FLASH_PAGE_SIZE                    (0x4000)
 #define BOARD_FLASH_SIZE            (FLASH_SIZE - CIRCUITPY_INTERNAL_NVM_SIZE- 0x2000 - 0xC000)
 
 #define BOARD_OSC_DIV               (24)

ports/stm/common-hal/microcontroller/__init__.c

@@ -116,7 +116,7 @@ const nvm_bytearray_obj_t common_hal_mcu_nvm_obj = {
     .base = {
         .type = &nvm_bytearray_type,
     },
-    .len = NVM_BYTEARRAY_BUFFER,
+    .len = NVM_BYTEARRAY_BUFFER_LEN,
     .start_address = (uint8_t*) (CIRCUITPY_INTERNAL_NVM_START_ADDR)
 };
 #endif

ports/stm/common-hal/nvm/ByteArray.h

@@ -32,7 +32,9 @@
 // STM flash is saved in sectors (not pages), at a minimum size of 16k.
 // To limit the RAM usage during writing, we want to set a smaller
 // maximum value.
-#define NVM_BYTEARRAY_BUFFER 512
+#ifndef NVM_BYTEARRAY_BUFFER_LEN
+#define NVM_BYTEARRAY_BUFFER_LEN 512
+#endif
 
 typedef struct {
     mp_obj_base_t base;