public void Send_ReadRxBuffer_Instruction(byte instructionFormat, RxBufferAddressPointer addressPointer, int byteCount)
{
byte[] expectedWriteBuffer = new byte[byteCount + 1];
expectedWriteBuffer[0] = instructionFormat;
var mcp25xxxSpiDevice = new Mcp25xxxSpiDevice();
Mcp25xxx mcp25xxx = new Mcp25625(mcp25xxxSpiDevice);
mcp25xxx.ReadRxBuffer(addressPointer, byteCount);
Assert.Equal(expectedWriteBuffer, mcp25xxxSpiDevice.LastWriteBuffer);
Assert.Equal(byteCount, mcp25xxxSpiDevice.LastReadBuffer.Length - 1);
}
private static void ReadRxBuffer(Mcp25xxx mcp25xxx, RxBufferAddressPointer addressPointer, int byteCount)
{
byte[] data = mcp25xxx.ReadRxBuffer(addressPointer, byteCount);
Console.Write($"{addressPointer,10}: ");
foreach (byte value in data)
{
Console.Write($"0x{value:X2} ");
}
Console.WriteLine();
}
/// <summary>
/// When reading a receive buffer, reduces the overhead of a normal READ
/// command by placing the Address Pointer at one of four locations for the receive buffer.
/// </summary>
/// <param name="addressPointer">The Address Pointer to one of four locations for the receive buffer.</param>
/// <param name="byteCount">Number of bytes to read. This must be one or more to read.</param>
/// <returns>The value of address read.</returns>
public byte[] ReadRxBuffer(RxBufferAddressPointer addressPointer, int byteCount = 1)
{
if (byteCount < 1)
{
throw new ArgumentException($"Invalid number of bytes {byteCount}.", nameof(byteCount));
}
const int StackThreshold = 31; // Usually won't read more than this at a time.
Span <byte> writeBuffer =
byteCount < StackThreshold ? stackalloc byte[byteCount + 1] : new byte[byteCount + 1];
Span <byte> readBuffer =
byteCount < StackThreshold ? stackalloc byte[byteCount + 1] : new byte[byteCount + 1];
// This instruction has a base value of 0x90.
// The 2nd and 3rd bits are used for the pointer address for reading.
writeBuffer[0] = (byte)((byte)InstructionFormat.ReadRxBuffer | ((byte)addressPointer << 1));
_spiDevice.TransferFullDuplex(writeBuffer, readBuffer);
return(readBuffer.Slice(1).ToArray());
}
