Download ALS-8 Program Devopment System Operator`s Manual

IODR /TVTWT/
0
IODR
SYSIO E200
TAPES DF00
E240
DF40
SYSIO, shown in the above, is the default I/O driver which
handles the main terminal. It remains the current driver until
another from the list is explicitly defined by IODR in yet
another form: IODR with just a name argument. Making a driver
"current" assumes that the corresponding routines are loaded and
ready for use because the subsequent ALS-8 commands will have
switched to using those addresses for I/O. Assuming that
"TAPES" in these examples represents drivers for a cassette
recording unit, data could be loaded into memory with the
following:
IODR
ENTR
(the
not
/TAPES/
200
ENTR function will retrieve data from the cassette and
the terminal keyboard)
The discussion on drivers so far has covered only the basic
duties of drivers. Because the system only has to know where
the routine starts, the programmer has an enormous amount of
flexibility. The driver is a program capable of handling any
number of devices in a single call if desired. It has access to
system parameters and tables so it can check status words or
find file information. When used with functions like ENTR, the
driver can accept data in whatever form the device will provide
it and then reformat it so that the necessary address and colon
are appended to the start of each line. There is also no
restriction that more than one driver can't be assigned to a
single device. One line printer driver might simply echo the
data given to it on the page. Another driver in the list might
count lines so it can automatically skip the paper folds and
print headings at page tops. Similarly, a set of drivers could
exist for communication with the VDM as within the TXT-2
extension package.
These capabilities are futher enhanced by the fact that any
user program has access to the driver list. It can, if desired,
ignore the "current" driver pair, search the table for a
specific name, retrieve the corresponding addresses and begin
using those routines. To write such a program, the user must
know the addresses of the table, the parameter identifying the
current driver, and the ALS-8 routines which search tables. The
conventions for the routines and memory storage must also be
learned, but the enormous flexibility compensates for the
trouble.
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