Q:
How do I specify and control Open Transport Serial port I/O handshaking?
The options seem a bit confusing.
A:
By using the the SRL_OPT_HANDSHAKE Option provided by the Open Transport native
interfaces you can customize serial port handshaking in variety of ways. For instance,
you can request that input handshake be controlled by the CTS line, or by the XON/OFF
sequence. The handshaking behavior is specified by a 4-byte unsigned integer value that
is passed in with the SRL_OPT_HANDSHAKE Option:
+=====-========-========-========-========-========-========-========-========+
| Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|Byte | | | | | | | | |
|=====+========+========+=====================================================|
| 0 | | | | | | | | |
|-----+-----------------------------------------------------------------------|
| 1 | | | | | DTR | CTS | XON/OFF| XON/OFF|
| | | | | | Output | Input | Input | Output |
|-----+-----------------------------------------------------------------------|
| 2 | XON character |
|-----+-----------------------------------------------------------------------|
| 3 | XOff character |
+=============================================================================+
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The high word (16 bits) of the integer is a bitmap with 1 or more of the following bits set:
kOTSerialXOnOffInputHandshake = 1
kOTSerialXOnOffOutputHandshake = 2
kOTSerialCTSInputHandshake = 4
kOTSerialDTROutputHandshake = 8
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The 2nd lowest byte is the XOn character value; the lowest byte is the XOff character value.
If these values are 0, and XOnOff handshaking was requested, the default values of
Control-S for XOff and Control-Q for XOn will be used.
There is an inline function (or #define for C users)
SerialHandshakeData(type, onChar, offChar)
defined in OpenTptSerial.h can be used to create this 4-byte value. The default value
of this option is no handshaking.
For instance, if you wish to enable XON/XOFF input handshaking, but you wanted to specify
that the XON char be a ^T instead of an ^Q. You would create an option structure in this manner.
TOption opt;
opt.len = kOTFourByteOptionSize;
opt.level = XTI_GENERIC;
opt.name = SERIAL_OPT_HANDSHAKE;
opt.value = OTSerialHandshakeData (
kOTSerialXOnOffInputHandshake,
('T' & ~0x40),
// normally kOTSerialDefaultOnChar
kOTSerialDefaultOffChar);
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You also have the ability to control the XOff state of the serial input port by using the the I_SetSerialXOffState Ioctl command. A value of 0 will unconditionally clear the XOFF state, while a value of 1 will unconditionally set it.
OTIoctl(theSerialEndpoint, I_SetSerialXOffState, 1); // Set XOFF state to ON
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The I_SetSerialXOn Ioctl causes the serial port to send an XON character. A value of
0 will only cause it to be sent if we're in the XOFF state, while a value of 1 will
unconditionally send the character.
OTIoctl(theSerialEndpoint, I_SetSerialXOn, 1); // Unconditionally send an XON
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Conversely, the I_SetSerialXOff Ioctl causes the serial port to send an XOFF character. A
value of 0 will only cause it to be sent if we're in the XON state, while a value
of 1 will unconditionally send the character.
OTIoctl(theSerialEndpoint, I_SetSerialXOff, 1); // Unconditionally send an XOFF
|
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