OMAPL13x EDMA to handle ADC samples via SPI bus

Yehonadav S.

Prodigy 150 points

Other Parts Discussed in Thread: OMAPL138

Hi everyone,

We have the following application: OMAP L132 reading ADC samples via SPI.

The ADC produces a single data ready (DRDY) interrupt and then the C6748 core starts to read 8x16bit words via SPI.

We are interested in changing this low level driver, which takes a lot of CPU time, to an EDMA application.

Is it possible to perform such transfer using EDMA? We couldn't find anythng suitable on the TRM.

Thank you in advance.

Yeho.

over 9 years ago

0 Sivaraj Kuppuraj over 9 years ago

TI__Mastermind 35645 points

Hi,

Yes, you could perform such transfers using EDMA driven instead of CPU driven data transfer.

Programing Sequence for DMA Mode, please refer the below wiki page.

http://processors.wiki.ti.com/index.php/StarterWare_SPI

http://processors.wiki.ti.com/index.php/StarterWare_01.10.01.01_User_Guide

May be, you could start with starterware SPI-EDMA example which would be a better benchmark and you could see the project and source file paths from the below after starterware installation:

Project path:

~\OMAPL138_StarterWare_1_10_04_01\build\c674x\cgt_ccs\omapl138\lcdkOMAPL138\spi_edma

Source path:

~\OMAPL138_StarterWare_1_10_04_01\examples\lcdkOMAPL138\spi_edma

Also, there are examples for C674x which are based on DSP/BIOS drivers: PSP (platform support package).

Getting started with C6748 DSP on the OMAPL138 is described here:

http://processors.wiki.ti.com/index.php/Getting_Started_Guide_for_C6748

If you are looking for register CSL kind of examples, you can find that under pspdrivers_xx_xx_xx\packages\ti\pspiom\cslr\evm6748\examples.

There is a SPI example in the PSP package which configures the peripheral in master mode.

Also, please refer the below E2E posts for servicing SPI using EDMA:

http://e2e.ti.com/support/dsp/tms320c6000_high_performance_dsps/f/115/t/213724.aspx

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/30083.aspx

Thanks & regards,

Sivaraj K

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0 Yehonadav S. over 9 years ago in reply to Sivaraj Kuppuraj

Prodigy 150 points

Hi Sivaraj,

Thank you for your quick response.

I've already went through the guides and examples you've posted, but still have something that I don't grasp:
Our application has only 1 DRDY trigger after which 8 words must be read - but not at once:
The 8 words must be read separately: a single word must be written to the SPI TX buffer, then
we wait for the SPI_RXBUF_FULL event. so far everything is OK.
But if we only have 2 EDMA channels - one triggered by the SPI_TXBUF_EMPTY and one triggered by SPI_RXBUF_FULL,
then these EDMA transactions will be triggered endlessly (once the TXBUF is empty - a new word will be sent, and once the RXBUF is full a new word will be read from it) because even after 8 words were read, any new word on TXBUF will trigger an SPI transmission of dummy zeros but the SPI_RXBUF_FULL event will still be triggered.

I still don't understand how to end this loop.

Edit: It seems that this type of application requires a strong CPU intervention in the process - once a word was read from SPIBUF, a completion interrupt must signal the CPU, and the CPU must hold an internal counter to decide whether 8 words have already read or not, and then to break the loop by disabling these EDMA channels until another DRDY signal comes in. Am I right here?

Thanks again,

Yehonadav.

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OMAPL13x EDMA to handle ADC samples via SPI bus