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1992-07-28
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Here are some notes on writing device drivers; before reading
them, you should familiarize yourself with the information in
"filesys.doc", especially the material on device drivers.
Serial Port Device Drivers
Serial port device drivers should recognize the
following ioctl calls:
(here "f" is always a FILEPTR referring to an open
file on the device)
ioctl(f, TIOCIBAUD, long *r):
Set input speed. "r" is a pointer to a 32 bit value, and is both an
input and output parameter. If *r is > 0, it represents the value
to which the serial port's input speed should be set. This value
is a long word representation of the speed in bits per second,
e.g. to set 9600 bits per second *r should be 9600L.
If *r is 0, it indicates that DTR should be dropped.
If *r is < 0, the call is an inquiry call only.
On return, *r is set to the value of the input speed before the
ioctl call was made. If, for some reason, this value is unknown,
*r is set to -1L.
Returns:
0 on success
ERANGE if the requested input speed is not available. In this case,
the input speed has not been changed, and is still returned in *r.
ioctl(f, TIOCOBAUD, long *r):
Set output speed. "r" is a pointer to a 32 bit value, and is both an
input and output parameter. If *r is > 0, it represents the value
to which the serial port's output speed should be set. This value
is a long word representation of the speed in bits per second,
e.g. to set 9600 bits per second *r should be 9600L.
If *r is 0, it indicates that the device should be hung up, i.e.
that DTR should no longer be asserted.
If *r is < 0, no change is to be made to the output speed.
On return, *r is set to the value of the output speed before the
ioctl call was made. If, for some reason, this value is unknown,
*r is set to -1L.
Returns:
0 on success
ERANGE if the requested output speed is not available. In this case,
the input speed has not been changed, and is still returned in *r.
Note: For many devices both the input and output speeds must always be
the same. For such devices, TIOCIBAUD and TIOCOBAUD may affect both
input and output speed.
ioctl(f, TIOCSBRK, dummy):
Causes a BREAK condition to be set on the output line.
Returns:
0 on success
EINVFN if the serial port cannot send BREAK
ioctl(f, TIOCCBRK, dummy)
Causes any existing BREAK condition to be cleared.
Returns:
0 on success
EINVFN if the serial port cannot send BREAK
ioctl(f, TIOCGFLAGS, short *flags)
Get the terminal control flags bits. 16 bit flag word
pointed to by "flags" is set to reflect the current
terminal state, as follows:
TF_STOPBITS 0x0003
The two low order bits describe the stop bits:
0x0000 illegal -- attempts to set this value are
ignored
0x0001 1 stop bit
0x0002 1.5 stop bits
0x0003 2 stop bits
TF_CHARBITS 0x000C
The next two bits describe the number of bits
transmitted per character:
0x0000 8 bits per character
0x0004 7 bits per character
0x0008 6 bits per character
0x000C 5 bits per character
The final nybble contains miscellaneous flags:
T_TANDEM 0x1000 ^S/^Q flow control active
T_RTSCTS 0x2000 RTS/CTS flow control active
T_EVENP 0x4000 even parity enabled
T_ODDP 0x8000 odd parity enabled
(note: T_EVENPAR and T_ODDPAR are mutually exclusive)
All other bits are reserved, and should be set to 0.
Returns:
0 on success
ioctl(f, TIOCSFLAGS, short *flags)
Set the terminal control flags (see the description
of TIOCGFLAGS for details) based on the values in the
word pointed to by "flags".
Returns:
0 on success
ERANGE if an illegal or unsupported combination of flags
is detected.
INTERFACE WITH EXISTING TIOCSETP/TIOCGETP CALLS:
The MiNT kernel will automatically make appropriate
TIOCIBAUD, TIOCOBAUD, TIOCGFLAGS, and TIOCSFLAGS calls
whenever a TIOCSETP or TIOCGETP Fcntl is made on a
terminal. The kernel will convert a Unix style baud
specification into a MiNT style one, as follows:
value of sg_ispeed or value sent to
sg_ospeed driver
#define B0 0 0L
#define B50 1 50L
#define B75 2 75L
#define B110 3 110L
#define B134 4 134L
#define B150 5 150L
#define B200 6 200L
#define B300 7 300L
#define B600 8 600L
#define B1200 9 1200L
#define B1800 10 1800L
#define B2400 11 2400L
#define B4800 12 4800L
#define B9600 13 9600L
#define B19200 14 19200L
#define B38400 15 38400L (*)
anything else -1L
(*) 38400 baud is not supported by the built
in device drivers, but may be by external drivers
If a speed other than those listed above is desired, the
TIOCIBAUD and/or TIOCOBAUD Fcntls should be used directly.