SPI Sending and Receiving at the Same Time Via Stream API

Hi Raghavendra,

thanks for your answer. Sorry for the big delay but Iam currently involved in another topic at work.

According to your answer:

I think your suggestion has to do with concurrent writes, but my problem is that I just want to "read and write" at the same time using the same stream, not "write and write" at the same time. Because the Stream_read-call issues the buffer and blocks until the buffer is reclaimed, the variable object->issues is greater than 0 (Stream_issue increments this variable, and only Stream_reclaim decrements it (when the buffer is reclaimed)) and my Stream_write call (which is concurrently issued to blocking Stream_read) fails and throws an exception if obj->issues is not equal zero. Is this intendet in a concurrent read-write scenario? Stream_read and Stream_write are using different buffers, so in my opinion there is no need to forbid concurrent read-write scenarios.

Is this a bug in the PS version Iam using or am I just missing something important?

Thanks for your help.

Kind Regards,

Steve

Hi Steve,

Which SPI Slave device are you using/communicating to?.

I am not clear with the following statement..

Steve Kreyer said:

I just want to "read and write" at the same time using the same stream,

can you please elaborate?..

If you refer the BIOSPSP Userguide, section 4.6.4 the NOTE section specifies that the "channel will be created only in DriverTypes_INOUT mode". Hope you are taking this into consideration. Also, can you please explain your test setup?. Or would it be possible to share your application project?.

Thanks & regards,

Raghavendra

Hi Raghavendra,

the slave device is the OMAP-L138 and Iam talking to a PPC host device (which serves as the SPI master). Please see the attachment for the test setup. This should make my issue clear.I've also wrote some comments to make it easier to understand.

Thanks for your time and effort.

Kind Regards,

Steve

Attachment

7230.spit_shortened.c.txt

Hi Steve,

Since Stream_write() / Stream_read() are synchronous calls(blocking), you cannot use it in multiple task scenario.

This is because when Stream_read() is called it blocks the present task and the next task gets the time slot to execute. As Stream_read() is already blocked in the task1, the BIOS does not allow subsequent Stream_ call in the task2, since stream layer maintains the number of buffers issued. 

You can refer – Stream.c file(placed in: ipc_1_20_00_23\packages\ti\sdo\io\Stream.c) function, Stream_submit(..) :  (obj->issued == 0) is where you are getting an exception.

Stream_write()/Stream_read() are equivalent to an Stream_issue()/Stream_reclaim() pair. Since you cannot use Strem_write() (as it is a synchronus call), replace it with Stream_issue () and Stream_reclaim() pair. Stream_issue() and Stream_reclaim() pair are asynchronous calls(non blocking) and can service multiple buffers, hence can be ideal for your requirement.

Replace Stream_write() with the following pair:

          Stream_issue(handle, buf, size, NULL, NULL);

          Stream_reclaim(handle, (Ptr *)&buf, BIOS_WAIT_FOREVER, NULL, NULL);

Secondly, when issuing two packets from a single handle you should make sure "maxIssues" of the streamParams is correctly set.

            /* This value should be equal to the number of buffers used in the application */

            streamParams.maxIssues = 10;

Hope this helps..

Thanks & regards,

Raghavendra

Hi Raghavendra,

I see. Thanks for the suggestion I will try that out and give you feedback in the next days.

Thanks,
Steve