Hi everyone.

I have a problem when I try to transmit data on SPI using PDC ( let's say array of 32 KB). The problem is next. I want to continuously transmit data on SPI using PDC and my oscilloscope show me that i have signal on MOSI and SCLK line which vary and that is ok. The problem is in my CS line which is always low, and I want to be high after every transmit data.

Also I try to transmit data on SPI without PDC and I didn't have that problem. My CS line was low during transmitting data and became high after data were transmitted.

I configured SPI: LASTXFER=0, PCS=0x0, PS=0, PCSDEC=0, CSAAT=0.
I also try to increase DLYBCT (Delay Between Consecutive Transfers) to 0xFF, I thought SPI will have enough time to put CS line to be high, but that never happened.

I use at91sam7x512 microcontroller.

Can anyone help me? Where I wrong, what do I miss?
Bane

hello,
if you software addresses only one spi slave then this behavior is "normal".
the only way to change it is insert a transfer to a not used spi "dummy" slave between each transfer to the regular "slave".
only drawback of this workaround:
it increases the needed memory size for the transfer buffer by a factor 2.

regards
gerhard

Thanks Gerhard,

I will try to change fixed peripheral select to variable peripheral select to see what is happening. I have not tried this feature because I thought it will work fine with only one peripheral. But obviously for fixed peripheral select chip select signal is always low when i use PDC and that is little stupid.

Any way thanks one more time. I'll write what I have achieved when i try it.

Regards
Bane

Hi everyone,

Sorry i was absent, but i had a problem with my oscilloscope, so i couldn't see my signals.

Anyway i change fixed peripheral select (PS=0) to variable peripheral select (PS=1) . I made array of type unsigned int, which is 32 bits wide with the data in the LSBs and the PCS and LASTXFER fields in the MSBs. On every even place of array i put my real data i want to transmit and on every odd place i put "dummy" data i want to transmit to "non-existent SPI" and everything work fine.

Now, i have one more question, something i don't understand from datasheet. When i transmitted data i try every combination of LASTXFER and CSAAT field and my transfer always work.
For: LASTXFER=0 , CSAAT=0;
LASTXFER=0 , CSAAT=1;
LASTXFER=1 , CSAAT=0;
LASTXFER=1 , CSAAT=1;

What is a real difference between LASTXFER and CSAAT and what is meaning of combination of these two fields?
Is it irrelevant combinations of this two field if i use it for SPI transfer with DMA, or combination of these two field is important if i use it for SPI without DMA?

Regards
Bane

hello,
regarding your last question:
use the following combination:
LASTXFER=0 , CSAAT=0;

regards
gerhard