DISK DRIVE OPERATION
6.4.30 Write Multiple Command (C5h)
This command is similar to the Write Sectors command. The drive sets BSY within 400 nsec of accepting the command, and interrupts are not presented on each sector but on the transfer of a block which contains the number of sectors defined by Set Multiple.
Command execution is identical to the Write Sectors operation, except that the number of sectors defined by the Set Multiple command are transferred without intervening interrupts. DRQ qualification of the transfer is required only at the start of the data block, not on each sector.
The block count of sectors to be transferred without intervening interrupts is programmed by the Set Multiple Mode command, which shall be executed prior to the Read Multiple command.
When the Write Multiple command is issued, the Sector Count register contains the number of sectors (not the number of blocks or the block count) requested.
If the number of requested sectors is not evenly divisible by the block count, as many full blocks as possible are transferred, followed by a final, partial block transfer. The partial block transfer is for n sectors, where
n = Remainder (Sector Count / Block Count)
If the Write Multiple command is attempted before the Set Multiple Mode command has been executed, or when Write Multiple commands are disabled, the Write Multiple operation is rejected with an aborted command error.
Disk errors encountered during execution of Write Multiple commands are posted after the attempted disk write of the block or partial block transfer. The Write Multiple command ends with the sector in error, even if it was in the middle of a block. Subsequent blocks are not transferred in the event of an error. Interrupts are generated when DRQ is set at the beginning of each block or partial block.
The contents of the Command Block registers, following the transfer of a data block which had a sector in error, are undefined. The host should retry the transfer as individual requests to obtain valid error information.
6.4.31 Write Sector(s) (30h:with retry, 31h:without retry)
This command writes from 1 to 256 sectors, as specified in the Sector Count register (a sector count of zero requests 256 sectors), beginning at the specified sector. Refer to Section 6.7 for the DRQ, IRQ and BSY protocol on data transfers.
If the drive is not already on the desired track, an implied seek is performed. Once at the desired track, the drive searches for the appropriate ID field.
If retries are disabled and two index pulses have occurred without
If retries are enabled, up to a predefined number of attempts may be made to read the requested ID before posting an error.
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