stm32u0: implement board_get_unique_id from UID_BASE

Previously stm32u0 had no board_get_unique_id(), so it fell back to the
weak default in hw/bsp/board.c and every board reported the placeholder
USB serial 0123456789ABCDEF. HIL identifies boards by USB serial, so a
non-unique serial collides on a multi-board rig. Read the 96-bit unique
ID from UID_BASE, mirroring stm32u5. Verified on stm32u083nucleo: now
enumerates as 300044000D5036394E373620.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

1 files changed, 13 insertions, 0 deletions

diff --git a/hw/bsp/stm32u0/family.c b/hw/bsp/stm32u0/family.c
index 7bd99fba6..0d20ba43f 100644
--- a/hw/bsp/stm32u0/family.c
+++ b/hw/bsp/stm32u0/family.c
@@ -166,6 +166,19 @@ uint32_t board_button_read(void) {
   return BUTTON_STATE_ACTIVE == HAL_GPIO_ReadPin(BUTTON_PORT, BUTTON_PIN);
 }
 
+size_t board_get_unique_id(uint8_t id[], size_t max_len) {
+  (void) max_len;
+  volatile uint32_t *stm32_uuid = (volatile uint32_t *) UID_BASE;
+  uint32_t *id32 = (uint32_t *) (uintptr_t) id;
+  uint8_t const len = 12;
+
+  id32[0] = stm32_uuid[0];
+  id32[1] = stm32_uuid[1];
+  id32[2] = stm32_uuid[2];
+
+  return len;
+}
+
 int board_uart_read(uint8_t* buf, int len) {
 #ifdef UART_ID
   int count = 0;