Can I interface TiVa to ADS8688?

Hello David,

There are 2 ways of doing the same: In Legacy and Advanced Mode for TM4C129

1. Use 4x 8-bit transfers or 2x16 with CS in GPIO Control
2. Use Advanced Mode in which the CS is controlled by the SSI but requires SW Intervention on frame end.

Regards
Amit

1. Do you mean manually control CS via GPIO?
2. For every frame?

If so, how to accomplish either under DMA mode?

Hello David

Option 1 is manual control of CS via GPIO.
Option 2 is for every frame. A Peripheral Scatter Gather may be employed.

Regards
Amit

According to the data sheet, Peripheral Scatter Gather: the transfers are controlled by a peripheral making a μDMA request. In ADS8688, it waits for the micro to retrieve the data, it doesn't make request

David Chance said:

...ADS waits for the micro to retrieve the data, it doesn't make request

Are you sure?   Usually - but not always - the ADC will have some means of signaling, "conversion completed."  

Minus that - there may exist an ADC "trigger" input - which must be "visited" by your controller - to initiate conversions.   If (again unlikely) that ADC cannot signal "conversion complete" you must "wait" till the data is complete/ready.   (which seems self-defeating in a "serious" ADC)

Reread of the ADC spec (focused per the above) seems in order...    (and that's your responsibility)

Hello David,

Then you can move to the Memory Scatter Gather which can be Software triggered.

Regards
Amit

This approach doesn't allow TiVa to retrieve data via DMA continously

Hello David,

You can write the Memory Scatter Gather to reinitialize itself. I do not have the example yet, but would surely now start working on it (after my vacations as part of the uDMA Application Note)

Regards
Amit

Are you sure TiVa can send out CS for the 32-bit data automatically for each sample via the DMA modes you mentioned?

Hello David,

The MSG works as a pseudo program. Delays have to be adjusted into it so that after CS is made low and transmission is started. On the other hand PSG can be started with a priming of the SSI Transmit buffer for the first transaction, When the SSIRX DMA interrupt is asserted, then PSG shall respond to it/.

Regards
Amit

I believe MSG totally leaves FFS to SSI, and SSI don't have FSS support for 32-bit data frame, I will have to wait and see your example

Hello David,

I would ask you to proceed with PSG or the Manual GPIO control for the moment so that you do not get gated on me/my application note.

Regards
Amit

I have already decided to use manual GPIO in ISR to get the prototype going, which may result a slower sample rate and higher CPU load.

To get the 500Ks/s with minimum CPU load, DMA (not just a DMA for the four bytes, but DMA continuously) is desirable, but I really doubt it would work even with the help of PSG or MSG mode

This is no ordinary ADC from TI

Hello David,

Yes. I do know that. There is an increasing demand on High bandwidth ADC in the past year and we are working on TM4C129 to be able to handle that kind of data traffic.

Regards
Amit