ARM7: LPC2148 & USB communication

UM10139 LPC214x User Manual
ics.nxp.com/.../user.manual.lpc2141.lpc2142.lpc2144.lpc2146.lpc2148.pdf

9.1 Set Address (Command: 0xD0, Data: write 1 byte)
The address set in the device will take effect after the status phase of the setup token.
(Alternately, issuing the Set Address command twice will set the address in the device immediately).

Then, the order of Set_Address process is,
1) execute Set Address command in protocol engine
2) send zero-length packet for acknowledgment to host (STATUS stage)

If you do it in reversed order, your device misses next request after Set_Address



> Can it be timing problem?

USB spec defines timeout for request process in details as follows.
The shortest timeout (50 ms) applies to Set_Address and Set_Configuration on enumeration.
If the firmware put debug output in 9600 baud, 48 characters of debug output causes 50 ms timeout.

9.2.6.3 Set Address Processing (usb_20.pdf p246)
After the reset/resume recovery interval, if a device receives a SetAddress() request, the device must be able to complete processing of the request and be able to successfully complete the Status stage of the request within 50 ms. In the case of the SetAddress() request, the Status stage successfully completes when the device sends the zero-length Status packet or when the device sees the ACK in response to the Status stage data packet.

9.2.6.4 Standard Device Requests
For standard device requests that require no Data stage, a device must be able to complete the request and be able to successfully complete the Status stage of the request within 50 ms of receipt of the request. This limitation applies to requests to the device, interface, or endpoint.

For standard device requests that require data stage transfer to the host, the device must be able to return the first data packet to the host within 500 ms of receipt of the request. For subsequent data packets, if any, the device must be able to return them within 500 ms of successful completion of the transmission of the previous packet. The device must then be able to successfully complete the status stage within 50 ms after returning the last data packet.

For standard device requests that require a data stage transfer to the device, the 5-second limit applies. This means that the device must be capable of accepting all data packets from the host and successfully completing the Status stage if the host provides the data at the maximum rate at which the device can accept it. Delays between packets introduced by the host add to the time allowed for the device to complete the request.

Tsuneo

UM10139 LPC214x User Manual
ics.nxp.com/.../user.manual.lpc2141.lpc2142.lpc2144.lpc2146.lpc2148.pdf

9.1 Set Address (Command: 0xD0, Data: write 1 byte)
The address set in the device will take effect after the status phase of the setup token.
(Alternately, issuing the Set Address command twice will set the address in the device immediately).

Then, the order of Set_Address process is,
1) execute Set Address command in protocol engine
2) send zero-length packet for acknowledgment to host (STATUS stage)

If you do it in reversed order, your device misses next request after Set_Address



> Can it be timing problem?

USB spec defines timeout for request process in details as follows.
The shortest timeout (50 ms) applies to Set_Address and Set_Configuration on enumeration.
If the firmware put debug output in 9600 baud, 48 characters of debug output causes 50 ms timeout.

9.2.6.3 Set Address Processing (usb_20.pdf p246)
After the reset/resume recovery interval, if a device receives a SetAddress() request, the device must be able to complete processing of the request and be able to successfully complete the Status stage of the request within 50 ms. In the case of the SetAddress() request, the Status stage successfully completes when the device sends the zero-length Status packet or when the device sees the ACK in response to the Status stage data packet.

9.2.6.4 Standard Device Requests
For standard device requests that require no Data stage, a device must be able to complete the request and be able to successfully complete the Status stage of the request within 50 ms of receipt of the request. This limitation applies to requests to the device, interface, or endpoint.

For standard device requests that require data stage transfer to the host, the device must be able to return the first data packet to the host within 500 ms of receipt of the request. For subsequent data packets, if any, the device must be able to return them within 500 ms of successful completion of the transmission of the previous packet. The device must then be able to successfully complete the status stage within 50 ms after returning the last data packet.

For standard device requests that require a data stage transfer to the device, the 5-second limit applies. This means that the device must be capable of accepting all data packets from the host and successfully completing the Status stage if the host provides the data at the maximum rate at which the device can accept it. Delays between packets introduced by the host add to the time allowed for the device to complete the request.

Tsuneo

Excerpt from KEIL USB device code

usbcore.c

/*
 *  USB Endpoint 0 Event Callback
 *    Parameters:      event
 *    Return Value:    none
 */

void USB_EndPoint0 (U32 event) {
  switch (event) {
    case USB_EVT_SETUP:                          // <----- SETUP transaction comes
      USB_SetupStage();
      USB_DirCtrlEP(SetupPacket.bmRequestType.BM.Dir);
      EP0Data.Count = SetupPacket.wLength;     /* Number of bytes to transfer */

      switch (SetupPacket.bmRequestType.BM.Type) {

        case REQUEST_STANDARD:
          switch (SetupPacket.bRequest) {

            case USB_REQUEST_SET_ADDRESS:        // <----- it is Set_Address request
              if (!USB_ReqSetAddress()) {        // <----- pass it to Set_Address handler
                goto stall_i;
              }
              USB_StatusInStage();
              break;
      ...
      ...

    case USB_EVT_IN :                            // <----- IN transaction just finishes
      if (SetupPacket.bmRequestType.BM.Dir == REQUEST_DEVICE_TO_HOST) {
        USB_DataInStage();                                               /* send data */
      } else {                                   // <----- this IN transaction is STATUS stage
        if (USB_DeviceAddress & 0x80) {          // <----- process specific to STATUS stage of Set_Address
          USB_DeviceAddress &= 0x7F;             // <----- recover original device address, masking flag bit
          USB_SetAddress(USB_DeviceAddress);     // <----- set the address to the engine
        }
      }
      break;  /* end case USB_EVT_IN */
      ...
      ...


/*
 *  Set Address USB Request
 *    Parameters:      None (global SetupPacket)
 *    Return Value:    TRUE - Success, FALSE - Error
 */

__inline BOOL USB_ReqSetAddress (void) {

  switch (SetupPacket.bmRequestType.BM.Recipient) {
    case REQUEST_TO_DEVICE:
      USB_DeviceAddress = 0x80 | SetupPacket.wValue.WB.L;     // <----- the address is kept on a variable with flag
      break;
    default:
      return (__FALSE);
  }
  return (__TRUE);
}


usbhw.c

/*
 *  USB Set Address Function
 *    Parameters:      adr:   USB Address
 *    Return Value:    None
 */

void USB_SetAddress (U32 adr) {
                                                 // <----- set the address to the engine, twice
  WrCmdDat(CMD_SET_ADDR, DAT_WR_BYTE(DEV_EN | adr)); /* Don't wait for next */
  WrCmdDat(CMD_SET_ADDR, DAT_WR_BYTE(DEV_EN | adr)); /*  Setup Status Phase */
}

Excerpt from LPCUSB

lpcusb.svn.sourceforge.net/.../usbstdreq.c

/**
        Local function to handle a standard device request

        @param [in]             pSetup          The setup packet
        @param [in,out] *piLen          Pointer to data length
        @param [in,out] ppbData         Data buffer.

        @return TRUE if the request was handled successfully
 */
static BOOL HandleStdDeviceReq(TSetupPacket *pSetup, int *piLen, U8 **ppbData)
{
        U8      *pbData = *ppbData;

        switch (pSetup->bRequest) {

        case REQ_GET_STATUS:
                // bit 0: self-powered
                // bit 1: remote wakeup = not supported
                pbData[0] = 0;
                pbData[1] = 0;
                *piLen = 2;
                break;

        case REQ_SET_ADDRESS:                     // <-------  Set_Address request handler
                USBHwSetAddress(pSetup->wValue);  // <-------  Set address to the engine before STATUS stage
                break;                            // <-------  like handling of other requests

        case REQ_GET_DESCRIPTOR:
                DBG("D%x", pSetup->wValue);
                return USBGetDescriptor(pSetup->wValue, pSetup->wIndex, piLen, ppbData);


lpcusb.svn.sourceforge.net/.../usbhw_lpc.c

/**
    Sets the USB address.

    @param [in] bAddr       Device address to set
 */
void USBHwSetAddress(U8 bAddr)
{
    USBHwCmdWrite(CMD_DEV_SET_ADDRESS, DEV_EN | bAddr);  // <-------  set the address to the engine, once
}

Both ways work. But which one is better for LPC family?
I take LPCUSB way.
The reason is two-fold,
1) It gives simpler code.
2) If we would take the traditional coding like KEIL, there is a chance that we miss the next request from host when the USB interrupt is disturbed by another higher-priority interrupts. The USB engine of NXP LPC family is designed to prevent this accident. There is no reason to
stick to the traditional coding, wasting up NXP effort ;-)

Tsuneo

http://www.keil.com/forum/docs/thread16320.asp