/// <summary>
/// Syncronously reads data from the BioHarness.
/// Handles the maximum message size constraints, splitting the
/// request into manageable chunks, and reassembling the response.
/// </summary>
/// <param name="offset">The byte to start read at</param>
/// <param name="length">The number of bytes to read</param>
/// <returns>A byte array conaining the requested data</returns>
private static byte[] SyncRead(int offset, int length)
{
CRC8 crc = new CRC8(0x8c);
var response = new byte[length];
var answer = new byte[133];
/* request = STX, MSG_ID_LOG, DLC, ... ETX */
byte[] request = new byte[] { STX, MSG_ID_GET_LOG, DLC, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, ETX };
var loop = length / 128;
if ((length % 128) > 0)
{
loop++;
}
int read = 0;
byte nb = 128;
do
{
if ((length - read) < 128)
{
nb = (byte)(length - read);
}
var offsetBytes = BitConverter.GetBytes(offset);
request[4] = offsetBytes[0];
request[5] = offsetBytes[1];
request[6] = offsetBytes[2];
request[7] = offsetBytes[3];
request[8] = nb;
request[9] = crc.Calculate(request.Skip(3).Take(6).ToArray());
vcp.Write(request, 0, 11);
int r = 0;
while ((r += vcp.Read(answer, r, nb + 5 - r)) < nb + 5)
{
}
Array.Copy(answer, 3, response, read, nb);
offset += nb;
read += nb;
}while (--loop > 0);
return(response);
}
/// <summary>
/// Read bytes from the device
/// </summary>
/// <param name="offset">Location or address in the device</param>
/// <param name="length">Number of bytes to read</param>
/// <param name="ok">A ref to a bool that indicates success</param>
/// <returns>An array of bytes read from the device</returns>
private static byte[] Read(int offset, int length, out bool ok)
{
var response = new byte[length];
var answer = new byte[133];
bool nak = false;
var loop = length / 128;
if ((length % 128) > 0)
{
loop++;
}
int read = 0;
byte nb = 128;
int badDataRetryCount = 0;
bool badData = false;
do /* Each 128 byte (max) frame */
{
do /* Retry up to BAD_DATA_RETRIES times when bad data is read */
{
badData = false;
if ((length - read) < 128)
{
nb = (byte)(length - read);
}
var offsetBytes = BitConverter.GetBytes(offset);
request[4] = offsetBytes[0];
request[5] = offsetBytes[1];
request[6] = offsetBytes[2];
request[7] = offsetBytes[3];
request[8] = nb;
request[9] = crc.Calculate(request.Skip(3).Take(6).ToArray());
vcp.Write(request, 0, 11);
int r = 0;
try
{
while ((r += vcp.Read(answer, r, nb + 5 - r)) < nb + 5)
{
/* Read into answer until full chunk is recieved */
}
}
catch
{
/* Typically timeout*/
nak = true;
}
if (r > 0)
{
/* Error checking */
/* Device said NAK */
if (answer[r - 1] == NAK)
{
nak = true;
break;
}
/* Check for device ACK */
if (answer[nb + 4] != ACK)
{
badData = true;
}
/* STX header */
if (answer[0] != STX)
{
badData = true;
}
/* MsgID header */
if (answer[1] != MSG_ID_GET_LOG)
{
badData = true;
}
/* Number of bytes read matches request */
if (answer[2] != nb)
{
badData = true;
}
/* CRC */
CRC8 frameCrc = new CRC8(0x8c);
byte crcVal = frameCrc.Calculate(answer.Skip(3).Take(nb).ToArray());
if (answer[nb + 3] != crcVal)
{
badData = true;
}
}
if (nak == true)
{
break;
}
if (badData)
{
badDataRetryCount++;
}
else
{
Array.Copy(answer, 3, response, read, nb);
offset += nb;
read += nb;
}
}while (badData && badDataRetryCount < BAD_DATA_RETRIES);
if (badData)
{
/* If we still had bad data after BAD_DATA_RETRIES then give up with NAK
* Read() function will be called once more externally on NAK (ok = false)
*/
nak = true;
break;
}
}while (--loop > 0); /* Next 128 byte frame */
ok = !nak;
return(response);
}
