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How to use pktend# and zlp# when using burst xfer? | Cypress Semiconductor

How to use pktend# and zlp# when using burst xfer?

Summary: 2 Replies, Latest post by thomastsai on 12 Nov 2014 09:10 PM PST
Verified Answers: 0
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byeyear's picture
31 posts


    I set burst length as 16 packets, and set packet size as 1024 bytes. If I want to read 16K bytes from host but only send 15K bytes from device side, should I assert pktend#(because of 15K < 16K) or zlp#(because of 1K boundary)?

rskv's picture
Cypress Employee
1134 posts


Let say if you have an FPGA connected to GPIF II interface of FX3 and you have configured FX3 to act as SlaveFIFO. Also, let say the buffer size that you are using in the firmware is 16KB.
Now if FPGA has written 15KB of data to FX3 and if FPGA does not have any more data then it needs to assert PKTEND# signal so that the received data will be committed to USB.

sai krishna.

thomastsai's picture
2 posts

I meet the same question. Are you sure we only need to assert pkend# on last word, then it seems could not work correct on 1K size boundary. DO I need to send zlp# again to termoinal this transaction ?

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