factor out timed transfer setup & err handling

The code for endpoint transfers and control transfers previously
had a bunch of duplicated logic for setup, timeout checking, and
result code error handling.

This change factors that stuff out into functions, using my new
transfer result error handling code from the last commit. Now the
endpoint and control transfers can share the setup, timeout, and
error check logic.

For me, this refactor reduced the firmware image size by 176 bytes.

Author: samblenny

shared-module/usb/core/Device.c

@@ -101,6 +101,59 @@ static bool _wait_for_callback(void) {
     return result == XFER_RESULT_SUCCESS;
 }
 
+static void _prepare_for_transfer(void) {
+    // Prepare for transfer. Unless there is a timeout, these static globals will
+    // get modified by the _transfer_done_cb() callback when tinyusb finishes the
+    // transfer or encounters an error condition.
+    _xfer_result = XFER_RESULT_INVALID;
+    _actual_len = 0;
+}
+
+static size_t _handle_timed_transfer_callback(tuh_xfer_t *xfer, mp_int_t timeout) {
+    if (xfer == NULL) {
+        mp_raise_usb_core_USBError(NULL);
+        return 0;
+    }
+    uint32_t start_time = supervisor_ticks_ms32();
+    while ((timeout == 0 || supervisor_ticks_ms32() - start_time < (uint32_t)timeout) &&
+           !mp_hal_is_interrupted() &&
+           _xfer_result == XFER_RESULT_INVALID) {
+        // The background tasks include TinyUSB which will call the function
+        // we provided above. In other words, the callback isn't in an interrupt.
+        RUN_BACKGROUND_TASKS;
+    }
+    if (mp_hal_is_interrupted()) {
+        // Handle case of VM being interrupted by Ctrl-C or autoreload
+        tuh_edpt_abort_xfer(xfer->daddr, xfer->ep_addr);
+        return 0;
+    }
+    // Handle control transfer result code from TinyUSB
+    xfer_result_t result = _xfer_result;
+    _xfer_result = XFER_RESULT_INVALID;
+    switch (result) {
+        case XFER_RESULT_SUCCESS:
+            return _actual_len;
+        case XFER_RESULT_FAILED:
+            mp_raise_usb_core_USBError(NULL);
+            break;
+        case XFER_RESULT_STALLED:
+            mp_raise_usb_core_USBError(MP_ERROR_TEXT("Pipe error"));
+            break;
+        case XFER_RESULT_TIMEOUT:
+            // This timeout comes from TinyUSB, so assume that it has stopped the
+            // transfer (note: timeout logic may be unimplemented on TinyUSB side)
+            mp_raise_usb_core_USBTimeoutError();
+            break;
+        case XFER_RESULT_INVALID:
+            // This timeout comes from CircuitPython, not TinyUSB, so tell TinyUSB
+            // to stop the transfer
+            tuh_edpt_abort_xfer(xfer->daddr, xfer->ep_addr);
+            mp_raise_usb_core_USBTimeoutError();
+            break;
+    }
+    return 0;
+}
+
 static mp_obj_t _get_string(const uint16_t *temp_buf) {
     size_t utf16_len = ((temp_buf[0] & 0xff) - 2) / sizeof(uint16_t);
     if (utf16_len == 0) {
@@ -225,38 +278,13 @@ void common_hal_usb_core_device_set_configuration(usb_core_device_obj_t *self, m
 }
 
 static size_t _xfer(tuh_xfer_t *xfer, mp_int_t timeout) {
-    _xfer_result = XFER_RESULT_INVALID;
+    _prepare_for_transfer();
     xfer->complete_cb = _transfer_done_cb;
     if (!tuh_edpt_xfer(xfer)) {
         mp_raise_usb_core_USBError(NULL);
         return 0;
     }
-    uint32_t start_time = supervisor_ticks_ms32();
-    while ((timeout == 0 || supervisor_ticks_ms32() - start_time < (uint32_t)timeout) &&
-           !mp_hal_is_interrupted() &&
-           _xfer_result == XFER_RESULT_INVALID) {
-        // The background tasks include TinyUSB which will call the function
-        // we provided above. In other words, the callback isn't in an interrupt.
-        RUN_BACKGROUND_TASKS;
-    }
-    if (mp_hal_is_interrupted()) {
-        tuh_edpt_abort_xfer(xfer->daddr, xfer->ep_addr);
-        return 0;
-    }
-    xfer_result_t result = _xfer_result;
-    _xfer_result = XFER_RESULT_INVALID;
-    if (result == XFER_RESULT_STALLED) {
-        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Pipe error"));
-    }
-    if (result == XFER_RESULT_INVALID) {
-        tuh_edpt_abort_xfer(xfer->daddr, xfer->ep_addr);
-        mp_raise_usb_core_USBTimeoutError();
-    }
-    if (result == XFER_RESULT_SUCCESS) {
-        return _actual_len;
-    }
-
-    return 0;
+    return _handle_timed_transfer_callback(xfer, timeout);
 }
 
 static bool _open_endpoint(usb_core_device_obj_t *self, mp_int_t endpoint) {
@@ -355,54 +383,12 @@ mp_int_t common_hal_usb_core_device_ctrl_transfer(usb_core_device_obj_t *self,
         .complete_cb = _transfer_done_cb,
     };
 
-    // Prepare for transfer. Unless there is a timeout, these static globals will
-    // get modified by the _transfer_done_cb() callback when tinyusb finishes the
-    // transfer or encounters an error condition.
-    _xfer_result = XFER_RESULT_INVALID;
-    _actual_len = 0;
-
+    _prepare_for_transfer();
     if (!tuh_control_xfer(&xfer)) {
         mp_raise_usb_core_USBError(NULL);
         return 0;
     }
-    uint32_t start_time = supervisor_ticks_ms32();
-    while ((timeout == 0 || supervisor_ticks_ms32() - start_time < (uint32_t)timeout) &&
-           !mp_hal_is_interrupted() &&
-           _xfer_result == XFER_RESULT_INVALID) {
-        // The background tasks include TinyUSB which will call the function
-        // we provided above. In other words, the callback isn't in an interrupt.
-        RUN_BACKGROUND_TASKS;
-    }
-    if (mp_hal_is_interrupted()) {
-        // Handle case of VM being interrupted by Ctrl-C or autoreload
-        tuh_edpt_abort_xfer(xfer.daddr, xfer.ep_addr);
-        return 0;
-    }
-    // Handle control transfer result code from TinyUSB
-    xfer_result_t result = _xfer_result;
-    _xfer_result = XFER_RESULT_INVALID;
-    switch (result) {
-        case XFER_RESULT_SUCCESS:
-            return _actual_len;
-        case XFER_RESULT_FAILED:
-            mp_raise_usb_core_USBError(NULL);
-            break;
-        case XFER_RESULT_STALLED:
-            mp_raise_usb_core_USBError(MP_ERROR_TEXT("Pipe error"));
-            break;
-        case XFER_RESULT_TIMEOUT:
-            // This timeout comes from TinyUSB, so assume that it has stopped the
-            // transfer (note: timeout logic may be unimplemented on TinyUSB side)
-            mp_raise_usb_core_USBTimeoutError();
-            break;
-        case XFER_RESULT_INVALID:
-            // This timeout comes from CircuitPython, not TinyUSB, so tell TinyUSB
-            // to stop the transfer
-            tuh_edpt_abort_xfer(xfer.daddr, xfer.ep_addr);
-            mp_raise_usb_core_USBTimeoutError();
-            break;
-    }
-    return 0;
+    return (mp_int_t)_handle_timed_transfer_callback(&xfer, timeout);
 }
 
 bool common_hal_usb_core_device_is_kernel_driver_active(usb_core_device_obj_t *self, mp_int_t interface) {