Commodore 1581 - Page 113

tion is located in the buffer which corresponds to the position of the
Controller Job Code in the Job Queue. For example, if the Controller
code in Job Queue position 2 (at location $0004) requests that a
logical sector of data be read, the data is put into Buffer 2 (at location
$0500).
Table 1 is a list of Controller Job Codes that can be put into the
Job Queue. Table 2 is a list of the codes that are returned by the
Controller once the job has been executed. The return code is placed
into the Job Queue in the same memory location that contained the
Controller Job Code. Consequently, the procedure to use the Control
ler is the following:
1) Write any parameters needed by the Job into the parameter
variables (HDSRS, HDRS2, SIDS).
2) Write the Controller Code into the Job Queue (JOBS).
3) Wait for the job to be completed by simply polling the loca
tion in JOBS where the Job code was put, and waiting for it to
change (bit 7 will be reset to 0).
TABLE 1: Controller JOB Command Codes
name code description
READ_DV $80 Reads a particular logical sector into the job
queue buffer (only if the disk has not been
changed). If the desired sector is already in the
track cache buffer, then no disk activity is re
quired (the data is merely transferred from the
track cache memory to the job queue buffer
memory). If the desired sector is not in the
track cache, then the current track cache is
dumped to disk (only if it has been modified),
the desired track is read into the track cache,
and finally the particular sector's data is trans
ferred from the track cache memory to the job
queue buffer.
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