Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 76)

II. SOFTWARE GUIDES - 8. Driver488/DRV 8E. Microsoft C
Personal488 User’s Manual, Rev. 3.0 II-61
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ERRNO holds the error code for I/O and other errors.
extern int errno;
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IOCTL_RD and IOCTL_WT are special versions of IOCTL_IO which reads and writes to the I/O
control channel of a device.
int ioctl_io(handle,chars,size,iocall)
int handle,
size,
iocall;
char chars[];
#define ioctl_rd(handle,chars,size) \
ioctl_io(handle,chars,size,0x4402)
#define ioctl_wt(handle,chars,size) \
ioctl_io(handle,chars,size,0x4403)
The I/O control channel of a device is read from and written to exactly as the normal (data)
channel is read and written, but the data transferred is not to be treated in the same way. Normally,
the I/O control channel is used to communicate setup and status information regarding the device
without actually transferring any data to or from it. When using Driver488/DRV,
IOCTL_WT is
used to force Driver488/DRV to be ready to accept a command, and IOCTL_RD is used to return
status information from the driver. These functions correspond exactly to the IOCTL and IOCTL$
commands, as described in “Section III: Command References.”
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CKLPINT, IEEE_CKI, and IEEE_ISR are functions and pointers which provide for automatic
interrupt detection and servicing.
int cklpint()
int _false_()
int (*ieee_cki)() = _false_
void no_op()
void (*ieee_isr)() = no_op
Driver488/DRV signals interrupts, which are enabled with the ARM command, by causing the light
pen signal to appear “true.” The CKLPINT checks that Driver488/DRV is able to service an
interrupt (the response from IOCTL_RD is 0 ) and then checks if an interrupt is pending by
checking the light pen status. The IEEEWT routine (described below) calls the function pointed to
by IEEE_CKI to determine if an IEEE interrupt needs to be serviced. The IEEE_CKI normally
points to the function _false_ which always returns zero ( 0 ). To enable interrupt checking
IEEE_CKI must be redirected to point to CKLPINT . Interrupt checking is disabled by pointing
IEEE_CKI back to _false_ . Once an interrupt has been detected, IEEEWT calls the interrupt
service routine pointed to by IEEE_ISR to service the interrupt. The IEEE_ISR initially points to
no_op , a function that does nothing, but it may be redirected as needed to specify the appropriate
interrupt service routine for each part of a program.
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_IEEEWT and _IEEERD are very similar to the unbuffered WRITE and READ routines provided in
the C library.
int _ieeewt(handle,chars)
int handle
char chars[]
int _ieeerd(handle,chars,size)
int handle,
size
char chars[]
#define ieeewt(chars) _ieeewt(ieee,chars)
#define ieeerd(chars) _ieeerd(ieee,chars,sizeof(chars))
The _IEEEWT differs from WRITE in that it checks for Driver488/DRV interrupts before writing,
determines the number of characters to write by using STRLEN , and prints an error message if an
error has occurred during writing. The _IEEERD differs from READ only in that it prints an error
message if an error has occurred during reading. IEEEWT and IEEERD (without the leading
underscore) write and read to the file IEEE . Notice that IEEERD uses SIZEOF to determine the
number of characters to read. This only works if SIZEOF can determine the number of bytes in the