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UPP configured in receive mode without START and ENABLE signals

Raghavendra Maddikery
Expert 5500 points


Hi Champs,

 

I have encountered a problem when using UPP in receive mode when the START and ENABLE signals are disabled. The application scenario is something like this:

>> Performing a EVM to EVM based transfer(Approx 1024 bytes of data). EVM A is configured in DUPLEX 0 mode(channel B as TX and Channel A as RX) and EVM B in DUPLEX 1 mode(channel B as RX and Channel A as TX).

Observations:

>> At the receiving end, when the START and ENABLE signals are enabled, the data transfers successfully.

>> At the receiving end, when the START and ENABLE signals are disabled, junk data is received.

Note: START and ENABLE signal configuration does not have any effect in transmit mode, since these signals are always driven by the transmitter.

But, If i refer the UPP SPRU section 2.5 indicates that the receive mode does not need these signals. Also, Sections 2.5.3 and 2.5.4 mentions that in receive mode the START and ENABLE signals may be disabled. But, in the section 2.5.7 (Timing Diagram) suggests that the receive mode expects START and ENABLE signals.

Can anyone please ellaborate the usage of these signals in receive mode?. I believe in the receive mode, START and ENABLE handshaking signals are required for proper data transfers. Correct me if I am wrong.. 

Please refer my customers query in the link: http://e2e.ti.com/support/embedded/f/355/p/120809/430792.aspx#430792

Setup:

EVMC6748 Rev3

PSP 01.30.01

 

Thanks & regards,
Raghavendra

  • 0
    TI__Expert 8890 points

    Raghavendra,

    The START and ENABLE signals are indeed optional in receive mode, but there are some caveats associated with this mode of operation.  You are ignoring all of the control signals except CLOCK, so the transmitter needs to be sure that it is sending valid data on every CLOCK pulse.

    In the linked post, you appear to be discussing a use case where two uPP peripherals are connected together (one transmitting, one receiving).  One important point to keep in mind is that the uPP peripheral always drives the CLOCK signal in transmit mode, even when no transfers are active.  This is a big problem if the receiver is ignoring START and ENABLE, since it will think that new data is constantly arriving even when the transmitter is idle.

    The only way to make the receiver operate correctly without START and ENABLE is to make the transmitter stop the CLOCK signal between data transfers.  The uPP peripheral doesn't support this operation in transmit mode, so you cannot ignore START and ENABLE when you're receiving data from another uPP peripheral.

    Hope this helps.

  • 0 in reply to Joe Coombs
    TI__Expert 5500 points

    Joe,

     

    Thank you for your reply. It was very helpful indeed..

     

    Thanks & regards,

    Raghavendra

     

  • 0 in reply to Joe Coombs
    Prodigy 40 points
    Joe,

    Questions regarding the operations when ignoring the START and ENABLE signals on a rx channel. In my setup, I "seem" to be recieving the correct data without stopping the clock that is driving the (FPGA) tx peripheral. In addition, there is a considerable amount of time between data transfers. Also, the OMPA DSP uPP RX Channel is configured to ignore the START and ENABLE signals however, the (FPGA) tx peripheral is still supplying those signals to the OMAP. Is there any explanations as to why I am getting the correct data, without stopping the clock ? Is is possilbe the the OMAP is still honoring the ENABLE signal, although it is configured to ignore it?

    Thanks