SPI receive FIFO in internal loopback mode

Luka Zitnik

Hello,

I am trying out the internal loopback mode of one of the SSI modules. I've noticed that when I make long enough delays in between reads from the data register, I can't get back the same data I send. I get only one value, a zero. Why is that happening. Isn't the receive FIFO there exactly for the purpose of retaining the data until it is needed?

over 9 years ago

0 Amit Ashara over 9 years ago

TI__Guru**** 244400 points

Hello Luka

Do you have the debugger view of the register open in your IDE?

Regards
Amit

0 cb1 over 9 years ago in reply to Amit Ashara

Guru 47900 points

Greetings Amit,

And - is use of the debugger to view such, "critical registers" fully & properly "discouraged" so that posters avoid this misfortune?

0 Amit Ashara over 9 years ago in reply to cb1

TI__Guru**** 244400 points

Hello cb1,

No. Not at this and other vendors. But we are still at early diagnosis of the issue, so let us wait for the poster to respond.

Regards
Amit

0 cb1 over 9 years ago in reply to Amit Ashara

Guru 47900 points

Amit,

I believe your precaution over-weighs this (individual) thread. Interference between IDE debugger and MCU - I feel - DOES WARRANT adequate alerting of your client-users!

0 Luka Zitnik over 9 years ago in reply to Amit Ashara

Prodigy 30 points

Hello Amit

SSI registers? This is what I have by the end of the execution of my test program.

0 Amit Ashara over 9 years ago in reply to Luka Zitnik

TI__Guru**** 244400 points

Hello Luka

1. Since the Data from SSI is read from a FIFO, having the register window during the program execution may cause the IDE to read the data from SSIRXFIFO instead of the CPU.
2. The second observation is that SSI_SR_RNE and RFF, means there is no data indeed.

I would suggesting sharing the code...

Regards
Amit

0 Luka Zitnik over 9 years ago in reply to Amit Ashara

Prodigy 30 points

Yes. It must be reading reading the FIFO. Now that I've closed the SSI0 window, the program can read all of the data that was sent.

Thank you very much for your time Amit.

0 Amit Ashara over 9 years ago in reply to Luka Zitnik

TI__Guru**** 244400 points

Hello Luka

Glad that solved the issue. Some IDE give the option to disable auto refresh. However it is always a good idea not to open the register window or memory window into the address space of peripherals which have FIFO or Auto Address Increment implementation.

Regards
Amit

0 cb1 over 9 years ago in reply to Amit Ashara

Guru 47900 points

Amit Ashara said:
it is always a good idea not to open the register window or memory window into the address space of peripherals which have FIFO or Auto Address Increment implementation.

Bravo, Amit.

Might it (also) be a good idea to "fully/properly" alert your client-users to this critical guidance?

So many fall victim to this (unexpected) happening - great care/concern for your users would be shown if this warning was (far) better conveyed!

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SPI receive FIFO in internal loopback mode