Datasheet

272 ep->next_pid = 1;
273 usb_start_transfer(ep, (uint8_t *) d, sizeof(struct usb_device_descriptor));
274 }
The usb_start_transfer function copies the data to send into the appropriate hardware buffer, and configures the buffer
control register. Once the buffer control register has been written to, the device controller will respond to the host with
the data. Before this point, the device will reply with a NAK.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/usb/device/dev_lowlevel/dev_lowlevel.c Lines 239 - 261
239 void usb_start_transfer(struct usb_endpoint_configuration *ep, uint8_t *buf, uint16_t len)
Ê {
240 // We are asserting that the length is <= 64 bytes for simplicity of the example.
241 // For multi packet transfers see the tinyusb port.
242 assert(len <= 64);
243
244 printf("Start transfer of len %d on ep addr 0x%x\n", len, ep->descriptor-
Ê >bEndpointAddress);
245
246 // Prepare buffer control register value
247 uint32_t val = len | USB_BUF_CTRL_AVAIL;
248
249 if (ep_is_tx(ep)) {
250 // Need to copy the data from the user buffer to the usb memory
251 memcpy((void *) ep->data_buffer, (void *) buf, len);
252 // Mark as full
253 val |= USB_BUF_CTRL_FULL;
254 }
255
256 // Set pid and flip for next transfer
257 val |= ep->next_pid ? USB_BUF_CTRL_DATA1_PID : USB_BUF_CTRL_DATA0_PID;
258 ep->next_pid ^= 1u;
259
260 *ep->buffer_control = val;
261 }
4.1.4. List of Registers
The USB registers start at a base address of 0x50110000 (defined as USBCTRL_REGS_BASE in SDK).
Table 407. List of USB
registers
Offset Name Info
0x00 ADDR_ENDP Device address and endpoint control
0x04 ADDR_ENDP1 Interrupt endpoint 1. Only valid for HOST mode.
0x08 ADDR_ENDP2 Interrupt endpoint 2. Only valid for HOST mode.
0x0c ADDR_ENDP3 Interrupt endpoint 3. Only valid for HOST mode.
0x10 ADDR_ENDP4 Interrupt endpoint 4. Only valid for HOST mode.
0x14 ADDR_ENDP5 Interrupt endpoint 5. Only valid for HOST mode.
0x18 ADDR_ENDP6 Interrupt endpoint 6. Only valid for HOST mode.
0x1c ADDR_ENDP7 Interrupt endpoint 7. Only valid for HOST mode.
0x20 ADDR_ENDP8 Interrupt endpoint 8. Only valid for HOST mode.
0x24 ADDR_ENDP9 Interrupt endpoint 9. Only valid for HOST mode.
RP2040 Datasheet
4.1. USB 416