6534 buffer size rules for pattern I/O

[Scott Payne]

Hello,

I'm using a 6534 to perform pattern I/O. I'm aware of the regenerate
data and loop from onboard memory options. My question concerns the
impact of the buffer size on the way the data is output. By this I
mean, the 6534 use's 32-byte DMA transfers by default. Therefore, if
you configure a buffer for 62 bytes and transmit on a single 8-bit
wide port the order of the data output does not match the order it was
placed in the buffer. Furthermore, the data sequence rotates with
each new transmission by 2-bytes. I assume the 2-bytes comes from the
fact that 62-bytes + 2-bytes = 64-bytes which is a multiple of
32-bytes (2*32 = 64). This is true for any combination of the
regenerate data and loop from onboard memory settings.
What are my
options if I only want to send 62-bytes each transmission not
64-bytes? I can think of two. 1) Use interrupt driven transfers, but
how does this impact the regenerate data and loop from onboard memory
settings. 2) Configure the buffer to be 64-bytes long and only apply
62 clock pulses each transmission. Hopefully, the output will start
at the beginning for each transmission and ignore the final 2-bytes of
data because these will not be defined.

Thanks in advance,
-Scott

[rgharrison]

Hi Scott,

If you choose to have your data regenerate, the 6534 will have no problem with buffer sizes that don't align to the DMA transfer size. As you mentioned, you can also choose to store the entire array in onboard memory and enable onboard looping. Technically, I don't think you would have to do either of your two suggestions to get this to work (for output). However, I have not tried this myself. I also know that if you are inputting data, DMA will only be successful if the data to be transferred is a multiple of the DMA transfer block size (32bytes).

If you do encounter problems on output similar to those on input with the DMA block sizes, then I would use your first suggestion, as this will yield proper operation. Your second suggestion is not
possible unless you clear the card and reconfigure the card each time! Anyway, hope that helps. Have a good day.

Ron