Add system/unique_board_id (#25)

Co-authored-by: Luke Wren <wren6991@gmail.com>

README.md

@@ -158,7 +158,7 @@ App|Description
 ---|---
 [hello_double_tap](system/hello_double_tap) | On dev boards with a reset button (but no BOOTSEL), a magic number in RAM can be used to enter the USB bootloader, when the reset button is pressed twice quickly.
 [narrow_io_write](system/narrow_io_write) | Demonstrate the effects of 8-bit and 16-bit writes on a 32-bit IO register.
-
+[unique_board_id](system/unique_board_id) | Read the 64 bit unique ID from external flash, which serves as a unique identifier for the board.
 ### Timer
 
 App|Description

system/CMakeLists.txt

@@ -2,4 +2,5 @@ if (NOT PICO_NO_HARDWARE)
     add_subdirectory(double_tap_usb_boot)
     add_subdirectory(narrow_io_write)
     add_subdirectory(hello_double_tap)
+    add_subdirectory(unique_board_id)
 endif ()

system/unique_board_id/CMakeLists.txt

@@ -0,0 +1,14 @@
+add_executable(unique_board_id
+        unique_board_id.c
+        )
+
+target_link_libraries(unique_board_id
+        pico_stdlib
+        pico_unique_id
+        )
+
+# create map/bin/hex file etc.
+pico_add_extra_outputs(unique_board_id)
+
+# add url via pico_set_program_url
+example_auto_set_url(unique_board_id)

system/unique_board_id/unique_board_id.c

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2021 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+
+#include "pico/stdlib.h"
+#include "pico/unique_id.h"
+
+// RP2040 does not have a unique on-board ID, but this is a standard feature
+// on the NOR flash it boots from. There is a 1:1 association between RP2040
+// and the flash, so this can be used to get a 64 bit globally unique board ID
+// for an RP2040-based board, including Pico.
+//
+// The pico_unique_id library retrieves this unique identifier during boot and
+// stores it in memory, where it can be accessed at any time without
+// disturbing the flash XIP hardware.
+
+int main() {
+    stdio_init_all();
+
+    pico_unique_board_id_t board_id;
+    pico_get_unique_board_id(&board_id);
+
+    printf("Unique identifier:");
+    for (int i = 0; i < PICO_UNIQUE_BOARD_ID_SIZE_BYTES; ++i) {
+        printf(" %02x", board_id.id[i]);
+    }
+    printf("\n");
+}