Increasing the Inter BYTE gap on DM6446 SPI using Linux

ArrowPete

The problem is that the time between bytes on the SPI line is too short. We need 10μs to 20μs to process each incoming byte. Originally the SPI port was running at 4MHz and was leaving only 0.9μs between bytes. We tried to use the C2TDELAY and T2CDELAY SPI features to add some delay between bytes. We also tried slowing down the baud rate. It was only possible to increase the inter-byte time to 2.15μs. It appears that the SPI port considers a word to be a single transaction, so it only inserts the expected delay between every other byte.

We are using Linux version 2.6.30

Is there a way to resolve this?

over 15 years ago

0 Paul.Yin over 15 years ago

TI__Genius 14405 points

Hi,

When you said the following

"We also tried slowing down the baud rate. It was only possible to increase the inter-byte time to 2.15μs. "

What's the bit rate that you chose? What's the min bit rate that you requrie?

I don't see any register other than SPIDELAY (which is what you are already playing with).

0 ArrowPete over 15 years ago in reply to Paul.Yin

Prodigy 30 points

Hi Paul,

The bit speed is not the issue, (we are down at 1MB/s) it is the time between bytes. We are communicating with a slow proccessor that needs about 20uS betwen bytes to figure out the correct response.

0 Paul.Yin over 15 years ago in reply to ArrowPete

TI__Genius 14405 points

Other than increasing the prescaler value (up to 255), there is probably no good way.

0 ArrowPete over 15 years ago in reply to Paul.Yin

Prodigy 30 points

Is it possible to send Bytes, one at a time. From the reference manual it indicates that you can, does the linux driver support this and if do how?

0 Paul.Yin over 15 years ago in reply to ArrowPete

TI__Genius 14405 points

I am unsure whether Linux supports it or not. Please post another message in the Linux forum. We cannot move it to that forum at this point.

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Increasing the Inter BYTE gap on DM6446 SPI using Linux