implement #19 serial descriptor based on deviceid

src/usb/usb.c

@@ -54,6 +54,13 @@
 extern tusb_desc_device_t usb_desc_dev;
 extern usb_desc_cfg_t     usb_desc_cfg;
 
+/* Serial should be different for Application mode, DFU with UF2, and DFU with CDC only therefore
+ * - DeviceID     : (Arduino + CircuitPython)
+ * - DeviceID + 1 : DFU with UF2
+ * - DeviceID + 2 : DFU with CDC only
+ */
+extern uint16_t           usb_desc_str_serial[1+16];
+
 /* tinyusb function that handles power event (detected, ready, removed)
  * We must call it within SD's SOC event handler, or set it as power event handler if SD is not enabled. */
 extern void tusb_hal_nrf_power_event(uint32_t event);
@@ -100,6 +107,8 @@ void usb_init(bool cdc_only)
     tusb_hal_nrf_power_event(NRFX_POWER_USB_EVT_READY);
   }
 
+  uint32_t devid_low = NRF_FICR->DEVICEID[0] + 1; // default uf2
+
   if ( cdc_only )
   {
     // Change PID to CDC only
@@ -108,6 +117,17 @@ void usb_init(bool cdc_only)
     // Remove MSC interface = reduce total interface + adjust config desc length
     usb_desc_cfg.config.bNumInterfaces--;
     usb_desc_cfg.config.wTotalLength -= sizeof(usb_desc_cfg.msc);
+
+    devid_low++;
+  }
+
+  // Create Serial string descriptor
+  char tmp_serial[17];
+  sprintf(tmp_serial, "%08lX%08lX", NRF_FICR->DEVICEID[1], devid_low);
+
+  for(uint8_t i=0; i<16; i++)
+  {
+    usb_desc_str_serial[1+i] = tmp_serial[i];
   }
 
   // Init tusb stack

src/usb/usb_desc.c

@@ -77,6 +77,9 @@ enum {
 // STRING DESCRIPTORS
 //--------------------------------------------------------------------+
 
+// Serial is 64-bit DeviceID -> 16 chars len
+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 [] =
 {
@@ -90,7 +93,7 @@ uint16_t const * const string_desc_arr [] =
     TUD_DESC_STRCONV('B','l','u','e','f','r','u','i','t',' ','n','R','F','5','2','8','4','0', ' ', 'D','F','U'),
 
     // 3: Serials TODO use chip ID
-    TUD_DESC_STRCONV('1', '2', '3', '4'),
+    usb_desc_str_serial,
 
     // 4: CDC Interface
     TUD_DESC_STRCONV('B','l','u','e','f','r','u','i','t',' ','S','e','r','i','a','l'),