IOIO locks up during SPI transaction with MCP-4131 any solutions?

Question

I am attempting to using an IOIO-RTG board to control a MCP-4131 digital potentiometer via SPI. I'm new to SPI but I believe that I've followed the SPI example. I'm able to set a resistance apparently but IOIO remains stuck afterwards. The only way to continue is to disconnect and reconnect to the board. I note that the SPI example expects a MISO and MOSI pin whereas the pot has a combined SDI/SDO pin. Is this difference the source of my issue?

IOIO RTG IOIOLIb 0326 Application Firmware 0506 Bootloader Firmware 0402 Hardware Sprk 0020

I've tried to implement asynchronous transactions to not wait for a response but the end result is the same. I've called the highgear function from within the Looper class and outside with no change.

class Looper extends BaseIOIOLooper
 {
   SpiMaster spi;

   protected void setup() throws ConnectionLostException
   {
            int clkPin = 39;//left side = 36
            int misoPin = 38;//left side = 33, not expecting output
            int mosiPin = 38;//left side = 35


           spi = ioio_.openSpiMaster(new DigitalInput.Spec(misoPin,
           Mode.PULL_UP), new DigitalOutput.Spec(mosiPin),
            new DigitalOutput.Spec(clkPin),
            new DigitalOutput.Spec[] { new DigitalOutput.Spec(40), new DigitalOutput.Spec(37),  },
            new SpiMaster.Config(Rate.RATE_125k, true, true));
   }

   public void highgear()
        {
            byte[] request = new byte[] {0,0,0,0,0,5,5,5};
            byte[] response = new byte[4];
            try {
                SpiMaster.Result result = spi.writeReadAsync(0, request, request.length, 7, response, 0);                
            } catch (ConnectionLostException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
}

The expected outcome is that the MCP with give the desired resistance and the IOIO will be available for further commanding. There are no errors as the board just freezes in it's set configuration.

Answer 1

The shared SDO/SDI pin of the MCP-4131 should not be the problem.

From the datasheet on page 31: "The 8-lead Single Potentiometer devices are pin limited so the SDO pin is multiplexed with the SDI pin (SDI/SDO pin). After the Address/Command (first 6-bits) are received, If a valid Read command has been requested, the SDO pin starts driving the requested read data onto the SDI/SDO pin."

As long as you only write to the digital potentiometer everything should be the same as with other SPI devices.

Have you tried your code with other SPI devices or even without connecting one?