use unique DevicID for usb serial

Author: hathach

ports/nrf/usb/usb.c

@@ -58,7 +58,7 @@ void usb_init(void) {
 
         sd_power_usbregstatus_get(&usb_reg);
     }else
-#else
+#endif
     {
         // Power module init
         const nrfx_power_config_t pwr_cfg = { 0 };
@@ -72,7 +72,6 @@ void usb_init(void) {
 
         usb_reg = NRF_POWER->USBREGSTATUS;
     }
-#endif
 
     if ( usb_reg & POWER_USBREGSTATUS_VBUSDETECT_Msk ) {
         tusb_hal_nrf_power_event(NRFX_POWER_USB_EVT_DETECTED);
@@ -82,6 +81,21 @@ void usb_init(void) {
         tusb_hal_nrf_power_event(NRFX_POWER_USB_EVT_READY);
     }
 
+    // create serial number based on device unique id
+    extern uint16_t usb_desc_str_serial[1 + 16];
+
+    char nibble_to_hex[16] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
+
+    for (int i = 0; i < 2; i++) {
+        for (int j = 0; j < 8; j++) {
+            uint8_t nibble = (NRF_FICR->DEVICEID[i] >> j * 4) & 0xf;
+
+            // Invert order since it is LE, +1 for skipping descriptor header
+            uint8_t  const idx = (15 - (i * 8 + j)) + 1;
+            usb_desc_str_serial[idx] = nibble_to_hex[nibble];
+        }
+    }
+
     tusb_init();
 
 #if MICROPY_KBD_EXCEPTION

ports/nrf/usb/usb_desc.c

@@ -78,6 +78,8 @@ enum {
 // STRING DESCRIPTORS
 //--------------------------------------------------------------------+
 
+uint16_t usb_desc_str_serial[1+16] = { TUD_DESC_STR_HEADER(16) };
+
 // array of pointer to string descriptors
 uint16_t const * const string_desc_arr [] =
 {
@@ -91,7 +93,7 @@ uint16_t const * const string_desc_arr [] =
     TUD_DESC_STRCONV('C','i','r','c','u','i','t','P','y',' ','n','R','F','5','2'),
 
     // 3 Serials TODO use chip ID
-    TUD_DESC_STRCONV('1', '2', '3', '4', '5'),
+    usb_desc_str_serial,
 
     // 4 CDC Interface
     TUD_DESC_STRCONV('C','i','r','c','u','i','t','P','y',' ','S','e','r','i','a','l'),