Max supported McBSP Speed - 28335

Arpan,

First thing to check would be that your IOs are set to asynchronous qualification via the GpioCtrlRegs.GPxQSEL registers.

Kris

Yeah Kris,

The GPIOs are configured as asynchronous.

Code Snippet -

GpioCtrlRegs.GPAQSEL2.bit.GPIO22 = GPIO_ASYNC; // Asynch output GPIO22 (MCLKXA)

GpioCtrlRegs.GPAQSEL2.bit.GPIO23 = GPIO_ASYNC; // Asynch output GPIO23 (MFSXA)

GpioCtrlRegs.GPAQSEL2.bit.GPIO20 = GPIO_ASYNC; // Asynch output GPIO20 (MDXA)

GpioCtrlRegs.GPAQSEL1.bit.GPIO7 = GPIO_ASYNC; // Asynch input GPIO7 (MCLKRA)

GpioCtrlRegs.GPAQSEL2.bit.GPIO21 = GPIO_ASYNC; // Asynch input GPIO21 (MDRA)

GpioCtrlRegs.GPAQSEL1.bit.GPIO5 = GPIO_ASYNC; // Asynch input GPIO5 (MFSRA)

- arpan

Is this using clock stop mode or the normal McBSP mode?

Kris

Kris,

I am using it in normal McBSP mode itself

- arpan

One question - can you run the McBSP independently of the DMA, and if so, what is your maximum speed?

(Just trying to see if it is the McBSP or DMA...)

Todd,

A few things I would suggest:

1) If you can, try just connecting your TX pins to your RX pins externally.  If you can't do this externally, there is an internal loopback mode you could use instead.  

2) There's no reason you would have to use the DMA.  I'm not sure I've ever heard of anyone not using it with the McBSP, but I do agree this is a good idea for debug.  There are McBSP interrupts you can configure or you can just poll the flags if you want to get really simple.

My guess is this is most likely just a configuration issue.  This module is a bit of a bear to setup.  Let me know how those tests go and we'll go from there.

Kris

Kris,

to 2):  There is a very good reason to use DMA for the McBSP:   the SPI - operating mode of the McBSP. Since the standard SPI is not accessible to DMA, the McBSP is the only way to use an external SPI - Device (e.g. memory) and the DMA to transfer data without the CPU.

Yes, this is why I was saying it is rare to use it without the DMA.  Most applications which use the McBSP are to have a SPI protocol with DMA access.

Kris