5 Replies Latest reply on Sep 24, 2011 7:05 AM by christian.richter

    slave fifo size

    john.liu

      Hi Guys,

         

         what max size of slave fifo can I configure to an endpoint? what event triggers the DMA between slave fifo and endpoint( slave fifo full/empty or endpoint buffer full/empty)? how to abort the dma?

         

       Thanks

        • 1. Re: slave fifo size
          anand.srinivasan.asokan

          The size variable of CyU3PDmaBuffer_t is 16-bit. This would be the restriction of buffer size.

             

          Once a USB packet (entire packet) is received it will be transmitted.

             

          Have you looked at CyU3PDmaChannelAbort??

             

          Regards,

             

          Anand

          • 2. Re: slave fifo size
            christian.richter

            Is the event for transferring data (manual mode) from slave fifo to IN endpoint also triggered in the case of terminating a short packet by asserting PKTEND hardware signal?

            • 3. Re: slave fifo size
              john.liu

              Anand, Thanks for your reply.

                 

               if the slave fifo size is limit by CyU3PDmaBuffer_t, it means the slave fifo physical size can be configured to 64KBytes. if the slave fifo is empty. the external processor can transfer a block data of 64KBytes without any interrupt, is it true?

                 

              thanks!

                 

              diagman

              • 4. Re: slave fifo size
                oliver.king-smith

                If I have an automatic DMA channel set between the GPIF and an IN type endpoint, can I have ZLP (zero length packet) produced, if the end of the GPIF transfer is exactly the same size as the packet length on the endpoint?

                   

                 

                   

                For example, I have the GPIF acting as consumer.  It gets a 1500 byte transfer before the PKTEND signal is asserted.  Assume the IN endpoint has a 1024 packet size.  I would expect the host to get a 1024 byte packet followed by a 476 byte packet.  Is this correct?

                   

                 

                   

                Now what happens if I get 1024 transfer on the GPIF before the PKTEND signal is asserted.  Can I get a ZLP sent after the 1024 byte frame goes to the host?  The old FX2 had a mechanism for inserting ZLPs, if the PKTEND was asserted on a boundary of the USB packet size.

                • 5. Re: slave fifo size
                  oliver.king-smith

                  I have answered part of the ZLP question I posted above.  The GPIF can generate a ZLP under certain condition.  According to the apnote AN65974, we can generate a ZLP by asserting PKTEND, while not asserting SLWR.

                     

                   

                     

                  This means the external processor needs to be aware of the USB packet size if it is to generate a ZLP.  Is there a way we can generate a ZLP from the ARM processor?

                  • 6. Re: slave fifo size
                    christian.richter

                    If you delay the PKTEND strobe you do not have to look at the packet size. We are using this mechanism at the FPGA to FX2 connection. 4 IFCLK cycles after the last word of the packet we generate the PKTEND strobe and do not transfer further data in this time. In the case there were a multiple of 512 bytes transferred a ZLP is generated. If the size was smaller then a full packet, the packet is commited without ZLP. This works great if the ZLP are allowed in the FX2 firmware. I think it will work on the FX3 in the same manner.