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BeagleBone McASP0 Tx always gives XUNDRN

sd v4l2
Prodigy 10 points

Hi 

I am currently experimenting with TI BeagleBone board McASP0 port. I am using polling mode only currently to send some data on AXR2 pin which configured as Tx pin. Got ACLKX and FSX as programmed, but for some reason, I don't see any data coming out of transmit line. I followed the instructions in

 http://processors.wiki.ti.com/index.php/StarterWare_McASP

I see that XDATA bit going low after calling McASPTxBufWrite(). As soon as McASPTxEnable() is called, it automatically sets the XUNDRN bit in XSTAT register. Also, sets the XDATA bit to High in XSTAT register.

Anybody can help to get something out of this Tx pin ? 

TIA,

SD.

  • 0
    TI__Intellectual 870 points

    Hi SD,

    A buffer underrun occurs when the serializer is instructed by the transmit state machine to transfer data from XRBUF[n] to XRSR[n], but XRBUF[n] has not yet been written with new data since the last time the transfer occurred. When this occurs, the transmit state machine sets the XUNDRN flag.

    Please make sure that new data is written to the transmit buffer before activating the transmitter.

    Regards,

    M.Jyothi Kiran