usb_device.c: Fix EP buffer size limitation for isochronous endpoints

The buffer size for USB endpoints was previously limited by the
endpoints buffer stride, which is 128 bytes * 2 for isochronous
endpoints and 64 bytes for bulk transfers.

According to the USB full-speed specification, the maximum frame size
can go up to 1023 bytes. The RP2040 microcontroller has 4KB of DPSRAM,
which can support this maximum frame size.

This commit removes the 128 bytes * 2 limitation for isochronous
endpoints, allowing support for the full 1023-byte frame size.

Signed-off-by: Khoa Hoang <[email protected]>

Author: maximus64

src/rp2_common/usb_device/include/pico/usb_device.h

@@ -87,8 +87,8 @@ typedef void (*usb_transfer_completed_func)(struct usb_endpoint *ep, struct usb_
 
 struct usb_buffer {
     uint8_t *data;
-    uint8_t data_len;
-    uint8_t data_max;
+    uint16_t data_len;
+    uint16_t data_max;
     // then...
     bool valid; // aka user owned
 };

src/rp2_common/usb_device/usb_device.c

@@ -52,6 +52,8 @@ static volatile uint32_t trace_i;
 #define usb_hw_set hw_set_alias(usb_hw)
 #define usb_hw_clear hw_clear_alias(usb_hw)
 
+#define ROUND_UP(x, align) (((x) + ((align) - 1)) & ~((align) - 1))
+
 void _usb_transfer_current_packet_only(struct usb_endpoint *ep);
 
 const struct usb_transfer_type usb_current_packet_only_transfer_type = {
@@ -229,9 +231,12 @@ static void _usb_endpoint_hw_init(struct usb_endpoint *ep, __unused uintptr_t da
     ep->dpram_buffer_offset = _device.next_buffer_offset;
     usb_debug("endpoint %d %s buf at %04x %04xx%d\n", ep_num, usb_endpoint_dir_string(ep), ep->dpram_buffer_offset,
               ep->buffer_size, _ep_buffer_count(ep));
-    uint32_t stride = _usb_endpoint_stride(ep);
-    if (ep->double_buffered) stride <<= 1u;
-    _device.next_buffer_offset += stride;
+    uint16_t stride = _usb_endpoint_stride(ep);
+    uint16_t buf_size_align = ROUND_UP(ep->buffer_size, stride);
+
+    if (ep->double_buffered) buf_size_align <<= 1u;
+
+    _device.next_buffer_offset += buf_size_align;
     assert(_device.next_buffer_offset <= USB_DPRAM_MAX);
     if (ep_num) {
         uint32_t reg = EP_CTRL_ENABLE_BITS
@@ -1137,10 +1142,12 @@ struct usb_interface *usb_interface_init(struct usb_interface *interface, const
 #if !PICO_USBDEV_BULK_ONLY_EP1_THRU_16
         if (USB_TRANSFER_TYPE_ISOCHRONOUS == (ep_desc->bmAttributes & USB_TRANSFER_TYPE_BITS)) {
             endpoints[i]->buffer_stride = 128 << PICO_USBDEV_ISOCHRONOUS_BUFFER_STRIDE_TYPE;
+            assert(ep_desc->wMaxPacketSize % endpoints[i]->buffer_stride == 0);
+            assert(ep_desc->wMaxPacketSize < 1024);
         } else {
             endpoints[i]->buffer_stride = 64;
+            assert(ep_desc->wMaxPacketSize <= endpoints[i]->buffer_stride);
         }
-        assert(ep_desc->wMaxPacketSize <= endpoints[i]->buffer_stride);
 #endif
     }
     return interface;