Support serial flash with 16 byte unique id

Flash devices like IS25LP016D have a 16 byte unique id. Reading just the
first 8 bytes causes devices to have duplicate unique ids as the numbers
only differ in the final 8 bytes.

Support overriding FLASH_UNIQUE_ID_SIZE_BYTES in the board header. Use
the final 8 bytes for the unique id.

Fixes raspberrypi#1641

src/rp2_common/hardware_flash/flash.c

@@ -19,7 +19,7 @@
 // Standard RUID instruction: 4Bh command prefix, 32 dummy bits, 64 data bits.
 #define FLASH_RUID_CMD 0x4b
 #define FLASH_RUID_DUMMY_BYTES 4
-#define FLASH_RUID_DATA_BYTES 8
+#define FLASH_RUID_DATA_BYTES FLASH_UNIQUE_ID_SIZE_BYTES
 #define FLASH_RUID_TOTAL_BYTES (1 + FLASH_RUID_DUMMY_BYTES + FLASH_RUID_DATA_BYTES)
 
 //-----------------------------------------------------------------------------

src/rp2_common/hardware_flash/include/hardware/flash.h

@@ -46,7 +46,9 @@
 #define FLASH_SECTOR_SIZE (1u << 12)
 #define FLASH_BLOCK_SIZE (1u << 16)
 
+#ifndef FLASH_UNIQUE_ID_SIZE_BYTES
 #define FLASH_UNIQUE_ID_SIZE_BYTES 8
+#endif
 
 // PICO_CONFIG: PICO_FLASH_SIZE_BYTES, size of primary flash in bytes, type=int, default=Usually provided via board header, group=hardware_flash
 

src/rp2_common/pico_unique_id/include/pico/unique_id.h

@@ -20,7 +20,7 @@ extern "C" {
  *
  * RP2040 does not have an on-board unique identifier (all instances of RP2040
  * silicon are identical and have no persistent state). However, RP2040 boots
- * from serial NOR flash devices which have a 64-bit unique ID as a standard
+ * from serial NOR flash devices which have at least a 64-bit unique ID as a standard
  * feature, and there is a 1:1 association between RP2040 and flash, so this
  * is suitable for use as a unique identifier for an RP2040-based board.
  *

src/rp2_common/pico_unique_id/unique_id.c

@@ -8,7 +8,7 @@
 #include "pico/bootrom.h"
 #include "pico/unique_id.h"
 
-static_assert(PICO_UNIQUE_BOARD_ID_SIZE_BYTES == FLASH_UNIQUE_ID_SIZE_BYTES, "Board ID size must match flash ID size");
+static_assert(PICO_UNIQUE_BOARD_ID_SIZE_BYTES <= FLASH_UNIQUE_ID_SIZE_BYTES, "Board ID size must at least be the size of flash ID");
 
 static pico_unique_board_id_t retrieved_id;
 
@@ -20,8 +20,16 @@ static void __attribute__((constructor)) _retrieve_unique_id_on_boot(void) {
         // debug, so just produce something well-defined and obviously wrong.
         for (int i = 0; i < PICO_UNIQUE_BOARD_ID_SIZE_BYTES; i++)
             retrieved_id.id[i] = 0xee;
-    #else
+    #elif (PICO_UNIQUE_BOARD_ID_SIZE_BYTES == FLASH_UNIQUE_ID_SIZE_BYTES)
         flash_get_unique_id(retrieved_id.id);
+    #elif (PICO_UNIQUE_BOARD_ID_SIZE_BYTES < FLASH_UNIQUE_ID_SIZE_BYTES)
+        // The flash id is >8 bytes (e.g. IS25LP016D) but we want to keep the
+        // pico unique board id as 8 bytes, just use the last 8 bytes which are likely to change
+        uint8_t flash_id[FLASH_UNIQUE_ID_SIZE_BYTES];
+        flash_get_unique_id(flash_id);
+        memcpy(retrieved_id.id, flash_id + FLASH_UNIQUE_ID_SIZE_BYTES - PICO_UNIQUE_BOARD_ID_SIZE_BYTES, PICO_UNIQUE_BOARD_ID_SIZE_BYTES);
+    #else
+        #error unique board id size is greater than flash unique id size
     #endif
 #else
     rom_get_sys_info_fn func = (rom_get_sys_info_fn) rom_func_lookup(ROM_FUNC_GET_SYS_INFO);