SPI timing issues

NETMF & Gadgeteer
1

I am interfacing Domino with an IMU I have (ADIS16350) with the initialization string below:

SPI.Configuration imuConfig = new SPI.Configuration((Cpu.Pin)ChipSelect_Port, false, 1, 1, true, true, 300, SPI.SPI_module.SPI1);

However the data I am tapping out doesn’t make sense at all… using the following code


        public void getData(double[] data)
        {
            inBuffer = new ushort[5];
            outBuffer = new ushort[5];
            outBuffer[0] = (ushort)(READ | XACCL_OUT);
            outBuffer[1] = (ushort)(READ | XGYRO_OUT);
            outBuffer[2] = (ushort)(READ | YGYRO_OUT);
            outBuffer[3] = (ushort)(READ | YACCL_OUT);
            outBuffer[4] = (ushort)(READ | ZACCL_OUT);
            pSPI.WriteRead(outBuffer, inBuffer);

            try
            {
                // output with conversion values
                data[0] = convert14toshort(inBuffer[0]) * 0.07326;    // °/s   xgyro
                data[1] = convert14toshort(inBuffer[1]) * 0.07326;    // °/s  ygyro
                data[2] = convert14toshort(inBuffer[2]) * 2.522;	  // mg xaccl
                data[3] = convert14toshort(inBuffer[3]) * 2.522;	  // mg yaccl
                data[4] = convert14toshort(inBuffer[4]) * 2.522;	  // mg zaccl
            }
            catch (IndexOutOfRangeException)
            {
                Debug.Print("Array too small");
            }
            finally
            {
                outBuffer = null;
                inBuffer = null;
            }
        }

I am suspecting the configuration string that is having problems. Would someone try to verify it and suggest a few improvements?

Thanks.

2

The configurations look OK. Try a slower clock. I see in accepts as low as 10KHz.
Do you have a digital analyzer to trace whats going on?

3

i get an invalidoperationexception error when i set to 10kHz

now running at about 200kHz

4

Ahh I found out my issue… Since the imu outputs a 14 bit data in a 16bit data frame, I was assuming the two MSBs are zero, as it was the case on my previous microcontroller. However bit 15 is set to 1 for some reasons, so I have to AND it out.

5

if first or last but is wrong then your data is shifted by one bit and this is usually the cause of nbot setting the clock correctly.

6

Update: This works…

 
        public void getData(double[] data)
        {
            inBuffer = new ushort[6];
            outBuffer = new ushort[6];
            outBuffer[0] = (ushort)(READ | XACCL_OUT);
            outBuffer[1] = (ushort)(READ | XGYRO_OUT);
            outBuffer[2] = (ushort)(READ | YGYRO_OUT);
            outBuffer[3] = (ushort)(READ | YACCL_OUT);
            outBuffer[4] = (ushort)(READ | ZACCL_OUT);
            outBuffer[5] = (ushort)(READ | SUPPLY_OUT);
            pSPI.WriteRead(outBuffer, inBuffer);
 
            try
            {
                // output with conversion values
                data[0] = convert14toshort(inBuffer[1]) * 0.07326;    // °/s   xgyro
                data[1] = convert14toshort(inBuffer[2]) * 0.07326;    // °/s  ygyro
                data[2] = convert14toshort(inBuffer[3]) * 2.522;	  // mg xaccl
                data[3] = convert14toshort(inBuffer[4]) * 2.522;	  // mg yaccl
                data[4] = convert14toshort(inBuffer[5]) * 2.522;	  // mg zaccl
            }
            catch (IndexOutOfRangeException)
            {
                Debug.Print("Array too small");
            }
            finally
            {
                outBuffer = null;
                inBuffer = null;
            }
        }