Transmitting over SSC using PDC at AT91SAM9261

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- Andreas Kuehn
  
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posted
16 years ago

Tue, Oct 2, 2007 7:03 AM

Hello out there...

I'm trying to send a block of data using the Peripheral DMA Controller (PDC) over the SSC-0. As transmitter and receiver of the SSC are independent and the PDC is full duplex capable, sending and receiving at the same time should be possible. But I can't get the PDC transfer going! Word by word transmissions work fine and the TK and TF signals are fine too. Nevertheless, if I activate the PDC I don't see any data running over the TD line.

Can you give me a hint on what is usually the "fault"? Or even an example for the AT91SAM92xx controller?

Thanks in advance akuehn

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posted
16 years ago

Tue, Oct 2, 2007 8:22 AM

I have the SSC running with the PDC but am not able to share the code (it was developed specifically for a customer). If you post your initialisation function I might be able to suggest something though.

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Richard.

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- Andreas Kuehn
  
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posted
16 years ago

Tue, Oct 2, 2007 9:59 AM

Here what I did so far. I mean register configuration of the SSC0 to perform a continuous data transfer of 16 long words per PDC call.

/** * Serial Synchronous Controller (SSC) definitions concerning * speed and protocoll. * */ #define SSC_WORD_SIZE 32 // Bit #define SSC_NUMBER_OF_WORDS 16 // WORDS #define SSC_PERIOD 0xff // (Bit x Words)/2 -1 #define SSC_FSLEN (1 -1) // length of frame sync bit #define SSC_DATNB (16 -1) // DATANB +1 #define SSC_DATLEN (32 -1) // Word length

#define RCMR_VAL ((SSC_PERIOD

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posted
16 years ago

Tue, Oct 2, 2007 11:58 AM

Hmm. There is nothing obvious. You make more use of the Atmel libraries than I do, so I presume some of the setup I do manually is done within your call to AT91F_SSC_Configure(), for example, setting up the baud rate and clocking modes.

I am also using PortB for outputs, whereas you seem to be using PortA. I presume this is just because of the pin multiplexing within the SAM7.

You are calling SetTx and SetNextTx from the initialisation routine, whereas I only call SetRx and SetNextRx from the initialisation, and call SetTx/SetNextTx when I actually have data to send. Could it be that the data being sent by these calls is completing prior to you configuring the interrupts? I don't think this can be the case unless the PDC is already in an enabled state though as you do not enable it until the end of your function. Just a thought.

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Regards,
Richard.

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- Andreas Kuehn
  
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posted
16 years ago

Tue, Oct 2, 2007 3:10 PM

Well yes! It's the same with me. I did move the PDC transfer/receive pointer stuff out of the initialization. It is now much clearer but I still have no data signals on my scope. Frame (TF) and Clock (TK) are realy fine and well detectable but no data. Okay. I have to go through the configuration again. Possibly there is something screwed up leaving the output desserted. ;-/

Thank you so far.

Regards akuehn

PS: Does someone else could give a comment?

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posted
16 years ago

Tue, Oct 2, 2007 3:22 PM

Double check that you have not inadvertently put the SSC into loopback mode. This would prevent the signals from being actually output. Running out of ideas after that :o(

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Regards,
Richard.

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- akuehn3
  
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posted
16 years ago

Tue, Oct 23, 2007 6:59 AM

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Hey out there...

I'm back from holidays and the problem is still there ;-)

In the meantime I cleared up my code sequence, deleted dublications and gave it something like a structure. The receiver reacts on every transmission frame signal but the sender does not send any data. Btw. SSC does not have a loopback mode. It's the SPI that comes with this feature. Again I went through the Atmel Manual and it is probably the PDC itself that comes with this limitation. On page 233 of the manual one can find the sentence: "The full-duplex peripherals feature eighteen mono-directional channels in pairs (transmit only or receive only)".

I'm not sure if I understand that right but it sounds like, you either transmit or receive using a PDC-channel. But it is possible to have two channels fully configured. Does that make sense to someone?

Cheers akuehn