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resets I2C pins back to original state, not blindly to input #59

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Merged
merged 1 commit into from
May 26, 2016
Merged

resets I2C pins back to original state, not blindly to input #59

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39 changes: 32 additions & 7 deletions Raspberry.IO.InterIntegratedCircuit/I2cDriver.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@ public class I2cDriver : IDisposable

private readonly ProcessorPin sdaPin;
private readonly ProcessorPin sclPin;
private readonly bool wasSdaPinSet;
private readonly bool wasSclPinSet;

private readonly IntPtr gpioAddress;
private readonly IntPtr bscAddress;
Expand Down Expand Up @@ -72,8 +74,9 @@ public I2cDriver(ProcessorPin sdaPin, ProcessorPin sclPin)
throw new InvalidOperationException("Unable to access device memory");

// Set the I2C pins to the Alt 0 function to enable I2C access on them
SetPinMode((uint) (int) sdaPin, Interop.BCM2835_GPIO_FSEL_ALT0); // SDA
SetPinMode((uint) (int) sclPin, Interop.BCM2835_GPIO_FSEL_ALT0); // SCL
// remembers if the values were actually changed to clear them or not upon dispose
wasSdaPinSet = SetPinMode((uint)(int)sdaPin, Interop.BCM2835_GPIO_FSEL_ALT0); // SDA
wasSclPinSet = SetPinMode((uint) (int) sclPin, Interop.BCM2835_GPIO_FSEL_ALT0); // SCL

// Read the clock divider register
var dividerAddress = bscAddress + (int) Interop.BCM2835_BSC_DIV;
Expand All @@ -89,9 +92,15 @@ public I2cDriver(ProcessorPin sdaPin, ProcessorPin sclPin)
/// </summary>
public void Dispose()
{
// Set all the I2C/BSC1 pins back to input
SetPinMode((uint) (int) sdaPin, Interop.BCM2835_GPIO_FSEL_INPT); // SDA
SetPinMode((uint) (int) sclPin, Interop.BCM2835_GPIO_FSEL_INPT); // SCL
// Set all the I2C/BSC1 pins back to original values if changed
if (wasSdaPinSet)
{
SetPinMode((uint)(int)sdaPin, Interop.BCM2835_GPIO_FSEL_INPT); // SDA
}
if (wasSclPinSet)
{
SetPinMode((uint)(int)sclPin, Interop.BCM2835_GPIO_FSEL_INPT); // SCL
}

Interop.munmap(gpioAddress, Interop.BCM2835_BLOCK_SIZE);
Interop.munmap(bscAddress, Interop.BCM2835_BLOCK_SIZE);
Expand Down Expand Up @@ -369,15 +378,31 @@ private static uint GetBscBase(ProcessorPin sdaPin, ProcessorPin sclPin)
}
}

private void SetPinMode(uint pin, uint mode)
/// <summary>
///
/// </summary>
/// <param name="pin"></param>
/// <param name="mode"></param>
/// <returns>True when value was changed, false otherwise.</returns>
private bool SetPinMode(uint pin, uint mode)
{
// Function selects are 10 pins per 32 bit word, 3 bits per pin
var paddr = gpioAddress + (int) (Interop.BCM2835_GPFSEL0 + 4*(pin/10));
var shift = (pin%10)*3;
var mask = Interop.BCM2835_GPIO_FSEL_MASK << (int) shift;
var value = mode << (int) shift;

WriteUInt32Mask(paddr, value, mask);
var existing = ReadUInt32(paddr) & mask;
if (existing != value)
{
//Console.WriteLine($"existing is {x} masked:{x & mask} vs mask:{mask} value:{value}");
WriteUInt32Mask(paddr, value, mask);
return true;
}
else
{
return false;
}
}

private static void WriteUInt32Mask(IntPtr address, uint value, uint mask)
Expand Down