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Two synchornous SPI DMA's - Is this possible?

Other Parts Discussed in Thread: ADS7863

Objective:

To obtain simultaneous data from two ADCs within ADS7863 ADC to two SPI buses on OMAP.

 

Architecture:

SDOa and SDOb – Two SPI outputs from ADS7863.

SPI1, SPI2 two SPI devices on OMAPL137.

The two SPI buses are connected as:

 

ADS7863              OMAPL137

SPOa                     SPI1 MISO.

SPOb                     SPI2 MISO

SDI                         SPI1 SIMO

CLK                         SPI 1 CLK

 

NC                          SP1 SIMO

NC                          SPI1 CLK

 

We need two DMA engines (or one) to get simultaneous sampled data from SDOa and SDOb lines connected to SPI1 and SPI2.

 

If this is not the right procedure to obtain simultaneous data from ADS7863 please give us suggestions on how to do this.

  • I don't see how this will work.  Based on my reading of the ADS7863 data sheet, the best bet is to configure the ADS7863 such that it uses only SDOA for transmitting data from both channels and disables SDOB completely (see "Serial Data Output (SDOx)" section in ADS7863 data sheet).  With that configuration you can hook up the pins as follows:

    ADS7863              OMAPL137

    SDOa                     SPI1 MISO.

    SDOb                     NC

    SDI                         SPI1 SIMO

    CLK                         SPI 1 CLK

  • Posting link to duplicate question:

    http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/p/54963/195415.aspx#195415

  • Using just SDOA reduces the sampling rate for 6 pseudo channels to about 333 ksps (=2Msps/6). We need over 600 sps for 6 each simultaneous channels. We were suggested to convert SPI2 to a slave with SPI1 to master. Let me know what do you think? 

    Architecture:

    SDOa and SDOb – Two SPI outputs from ADS7863.

    SPI1, SPI2 are two SPI devices on OMAPL137 with following configuration: SPI1 master and SPI2 slave.

    The two SPI buses are connected as:

     

    ADS7863              OMAPL137

    SPOa                     SPI1 MISO

    SPOb                     SPI2 SIMO 

    SDI                         SPI1 SIMO

    CLK                         SPI 1 CLK

     

    NC                          SP1 MISO

    SPI 1 CLK                SPI2 CLK   (SPI2 is clocked from SPI1).

     

  • Okay, if that this the case, then going with one SPI in master mode and another in slave mode would be your only option.  The pin hookup you have described looks correct to me.