EP0 OUT Transfers | Cypress Semiconductor
EP0 OUT Transfers
I'm having an issue with EP0BUF. Is it double buffered?
I've written a few control endpoint vendor functions to handle some low load functions in our firmware (transferring a few bytes). I've got most of the functions working which just do a single read, read two bytes, a write followed by a read, etc. Only one of these functions uses data from the PC in EP0BUF.
I have a switch statement which parses SETUPDAT. The part that reads EP0BUF is here:
//Write n bytes, buffer has data, addr, data, addr
//wValue = 0,0 SETUPDAT,SETUPDAT
//wIndex = 0, 0 SETUPDAT,SETUPDAT
//wLength = 0, len SETUPDAT,SETUPDAT
dat = *(EP0BUF+i);
addr = *(EP0BUF+i+1);
IOA = i;
EP0BCH = 0;
EP0BCL = 0; // Arm endpoint with # bytes to transfer
EP0CS |= bmHSNAK; // Acknowledge handshake phase of device request
WriteByte just sets addr to Port C and dat to Port B and then does a write cycle on a proprietary data bus connected to those ports.
The data that goes out on the bus is always one cycle old. For example:
1) Start device and initialize
2) PC writes several bytes to EP0 with vendor code VR_WRITE_N
3) First time, data out on the bus is random garbage
4) PC writes another set of bytes to EP0 with VR_WRITE_N
5) Data on the bus is the first data set sent.
WriteByte works because I use it for the single byte write functions which pass the address and data in wValue and wIndex and doesn't use EP0BUF. The only time I see a problem is with the VR_WRITE_N function. How do I get EP0BUF to have the latest data from the PC?