samd: convert usb to background task

Author: jepler

ports/atmel-samd/background.c

@@ -85,7 +85,6 @@ void run_background_tasks(void) {
     network_module_background();
     #endif
     filesystem_background();
-    usb_background();
     running_background_tasks = false;
     assert_heap_ok();
 

ports/atmel-samd/supervisor/usb.c

@@ -29,6 +29,13 @@
 #include "hpl/gclk/hpl_gclk_base.h"
 #include "hal_gpio.h"
 #include "lib/tinyusb/src/device/usbd.h"
+#include "supervisor/background_callback.h"
+#include "supervisor/usb.h"
+
+static background_callback_t callback;
+static void usb_background_do(void* unused) {
+    usb_background();
+}
 
 void init_usb_hardware(void) {
     #ifdef SAMD21
@@ -62,23 +69,28 @@ void init_usb_hardware(void) {
 #ifdef SAMD21
 void USB_Handler(void) {
     tud_int_handler(0);
+    background_callback_add(&callback, usb_background_do, NULL);
 }
 #endif
 
 #ifdef SAM_D5X_E5X
 void USB_0_Handler (void) {
-  tud_int_handler(0);
+    tud_int_handler(0);
+    background_callback_add(&callback, usb_background_do, NULL);
 }
 
 void USB_1_Handler (void) {
-  tud_int_handler(0);
+    tud_int_handler(0);
+    background_callback_add(&callback, usb_background_do, NULL);
 }
 
 void USB_2_Handler (void) {
-  tud_int_handler(0);
+    tud_int_handler(0);
+    background_callback_add(&callback, usb_background_do, NULL);
 }
 
 void USB_3_Handler (void) {
-  tud_int_handler(0);
+    tud_int_handler(0);
+    background_callback_add(&callback, usb_background_do, NULL);
 }
 #endif