ZiLOG System 8000 - Page 265

HRM Zilog
HRM
2) Host initializes the Dispatch Table with the addresses
of the packets for each drive. It also sets all packet
status (PSG to PS3) fields to IDLE. It is recommended
that the packets are also initialized to zeroes.
3) Host sends each of the following commands, polling
until SR:BZ clears after each command:
a)
CR:CMD
=
4
and
CR:DATA
=
l.s.byte of
Dispatch
Table
(DT)
address
b)
CR:CMD
5
and
CR:DATA
=
middle
byte
of
DT
address
c)
CR:CMD
=
6
and
CR:DATA
=
m. s . byte
of
DT
address
d)
CR:CMD
=
7
and
CR:DATA
=
interrupt
vector
(NOTE:
this must
be
done
even if
interrupt
mode is
not
used! )
4) Host sends CR:CMD = 1, then polls SR until SR:NDT
clears.
ISSUING PACKET COMMANDS
After the controller is initialized, it is ready to recetve
packet commands. All disk-control operations are packet
commands~ Packet commands may be issued in either polled
mode or interrupt mode. The programming sequence for packet
commands is:
1) Host sets up one or more packets with the appropriate
packet command opcode in CM:PCMD and sets all applica-
ble parameter fields. Bits which modify the behavior
of the controller on error conditions (such as CM:NR,
CM:NO, CM:NE and OF: bits) may also be set or cleared.
2) Host sets the PS field of each packet set up in step
to GO.
3) Host sends CR:WK with CR:EI optionally set. If CR:EI
is set, the controller will interrupt at completion of
each packet command.
4) The Controller reads all packets with DT:PS set to GO,
and sets the DT:PS field for each such packet to BUSY.
5) The Controller initiates seeks on drives with packet
commands requlrlng a seek. When seek is complete, or
if no seek was required, the command is performed and
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