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Clarify the logic in sendI2cCommand

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This commit is contained in:
PaulZC
2021-11-16 14:28:25 +00:00
parent 2f2d0a5951
commit 706dfb4cc6
1 changed files with 24 additions and 13 deletions
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src/SparkFun_u-blox_GNSS_Arduino_Library.cpp
+24 -13
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@@ -2933,7 +2933,6 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::sendCommand(ubxPacket *outgoingUBX, uint16_t
//Returns false if sensor fails to respond to I2C traffic
sfe_ublox_status_e SFE_UBLOX_GNSS::sendI2cCommand(ubxPacket *outgoingUBX, uint16_t maxWait)
{
// PaulZC : November 15th 2021
// From the integration guide:
// "The receiver does not provide any write access except for writing UBX and NMEA messages to the
// receiver, such as configuration or aiding data. Therefore, the register set mentioned in section Read
@@ -2949,7 +2948,7 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::sendI2cCommand(ubxPacket *outgoingUBX, uint16
// Point 2 is important. It means:
// * In this function:
// if we do multiple writes (because we're trying to write more than i2cTransactionSize),
// we may need to write one byte less in the previous write to ensure we always have two bytes left for the final write.
// we may need to write one byte less in the penultimate write to ensure we always have two bytes left for the final write.
// * In pushRawData:
// if there is one byte to write, or one byte left to write, we need to do the same thing and may need to store a single
// byte until pushRawData is called again.
@@ -2972,11 +2971,11 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::sendI2cCommand(ubxPacket *outgoingUBX, uint16
// i2cTransactionSize will be at least 8. We don't need to check for smaller values than that.
uint16_t bytesToSend = outgoingUBX->len + 8; // How many bytes need to be sent?
uint16_t bytesToSend = outgoingUBX->len + 8; // How many bytes need to be sent
uint16_t bytesSent = 0; // How many bytes have been sent
uint16_t bytesLeftToSend = bytesToSend; // How many bytes remain to be sent?
uint16_t bytesLeftToSend = bytesToSend; // How many bytes remain to be sent
uint16_t startSpot = 0; // Payload pointer
uint16_t startSpot = 0;
while (bytesLeftToSend > 0)
{
uint16_t len = bytesLeftToSend; // How many bytes should we actually write?
@@ -3007,15 +3006,21 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::sendI2cCommand(ubxPacket *outgoingUBX, uint16
bytesSent += 6;
uint16_t x;
for (x = 0; (x < outgoingUBX->len) && (bytesSent < len); x++) //Write a portion of the payload to the bus
uint16_t x = 0;
//Write a portion of the payload to the bus.
//Keep going until we reach the end of the payload (x == outgoingUBX->len)
//or we've sent as many bytes as we can in this transmission (bytesSent == len).
for (; (x < outgoingUBX->len) && (bytesSent < len); x++)
{
_i2cPort->write(outgoingUBX->payload[startSpot + x]);
bytesSent++;
}
startSpot += x;
if (bytesSent < len) //Do we need to write both checksum bytes? (Remember that bytesLeftToSend will be zero or >=2 here)
//Can we write both checksum bytes?
//We can send both bytes now if we have exactly 2 bytes left
//to be sent in this transmission (bytesSent == (len - 2)).
if (bytesSent == (len - 2))
{
//Write checksum
_i2cPort->write(outgoingUBX->checksumA);
@@ -3023,17 +3028,23 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::sendI2cCommand(ubxPacket *outgoingUBX, uint16
bytesSent += 2;
}
}
else if (bytesSent < bytesToSend) // Keep writing payload bytes - plus the checksum if required
else // Keep writing payload bytes. Write the checksum at the right time.
{
uint16_t x;
for (x = 0; (x < len) && ((startSpot + x) < (outgoingUBX->len)); x++) //Write a portion of the payload to the bus
uint16_t x = 0;
//Write a portion of the payload to the bus.
//Keep going until we've sent as many bytes as we can in this transmission (x == len)
//or until we reach the end of the payload ((startSpot + x) == (outgoingUBX->len))
for (; (x < len) && ((startSpot + x) < (outgoingUBX->len)); x++)
{
_i2cPort->write(outgoingUBX->payload[startSpot + x]);
bytesSent++;
}
startSpot += x;
if (bytesSent == (bytesToSend - 2)) //Do we need to write both checksum bytes? (Remember that bytesLeftToSend will be zero or >=2 here)
//Can we write both checksum bytes?
//We can send both bytes if we have exactly 2 bytes left to be sent (bytesSent == (bytesToSend - 2))
//and if there is room for 2 bytes in this transmission
if ((bytesSent == (bytesToSend - 2)) && (x == (len - 2)))
{
//Write checksum
_i2cPort->write(outgoingUBX->checksumA);
@@ -3042,7 +3053,7 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::sendI2cCommand(ubxPacket *outgoingUBX, uint16
}
}
if (bytesSent < bytesToSend) // Are we all done?
if (bytesSent < bytesToSend) // Do we need to go round the loop again?
{
if (_i2cPort->endTransmission(_i2cStopRestart) != 0) //Don't release bus unless we have to
return (SFE_UBLOX_STATUS_I2C_COMM_FAILURE); //Sensor did not ACK