shared/tinyusb: Schedule TinyUSB task function from dcd_event_handler.

dcd_event_handler() is called from the IRQ when a new DCD event is queued
for processing by the TinyUSB thread mode task.  This lets us queue the
handler to run immediately when MicroPython resumes.

Currently this relies on a linker --wrap hack to work, but a PR has been
submitted to TinyUSB to allow the function to be called inline from
dcd_event_handler() itself.

This work was funded through GitHub Sponsors.
Signed-off-by: Angus Gratton <angus@redyak.com.au>

shared/tinyusb/mp_usbd.c

@@ -27,17 +27,40 @@
 #include <stdlib.h>
 
 #include "py/mpconfig.h"
+#include "py/runtime.h"
 
 #if MICROPY_HW_ENABLE_USBDEV
 
 #ifndef NO_QSTR
 #include "tusb.h" // TinyUSB is not available when running the string preprocessor
+#include "device/dcd.h"
 #include "device/usbd.h"
 #include "device/usbd_pvt.h"
 #endif
 
+// Legacy TinyUSB task function wrapper, called by some ports from the interpreter hook
 void usbd_task(void) {
     tud_task_ext(0, false);
 }
 
+// TinyUSB task function wrapper, as scheduled from the USB IRQ
+static void mp_usbd_task(mp_sched_node_t *node);
+
+extern void __real_dcd_event_handler(dcd_event_t const *event, bool in_isr);
+
+// If -Wl,--wrap=dcd_event_handler is passed to the linker, then this wrapper
+// will be called and allows MicroPython to schedule the TinyUSB task when
+// dcd_event_handler() is called from an ISR.
+TU_ATTR_FAST_FUNC void __wrap_dcd_event_handler(dcd_event_t const *event, bool in_isr) {
+    static mp_sched_node_t usbd_task_node;
+
+    __real_dcd_event_handler(event, in_isr);
+    mp_sched_schedule_node(&usbd_task_node, mp_usbd_task);
+}
+
+static void mp_usbd_task(mp_sched_node_t *node) {
+    (void)node;
+    tud_task_ext(0, false);
+}
+
 #endif

shared/tinyusb/mp_usbd.h

@@ -29,9 +29,6 @@
 
 #include "py/obj.h"
 
-// Call instead of tud_task()
-void mp_usbd_task(void);
-
 // Function to be implemented in port code.
 // Can write a string up to MICROPY_HW_USB_DESC_STR_MAX characters long, plus terminating byte.
 extern void mp_usbd_port_get_serial_number(char *buf);