CMD_UPDATE/ETD_UPDATE - write out the track buffer if it is dirty.

The mfm.device does not write data sectors unless it is necessary (you request that a different track be used) or until the user requests that an update be performed. This improves system speed by caching disk operations. These commands ensure that any buffered data is flushed out to the disk. If the track buffer has not been changed since the track was read in, these commands do nothing. ETD_UPDATE command checks for diskchange.

io_Device

preset by the call to OpenDevice()

io_Unit

preset by the call to OpenDevice()

io_Command

CMD_UPDATE or ETD_UPDATE

io_Flags

0 or IOF_QUICK

iotd_Count

(ETD_UPDATE only) maximum allowable change counter value.

io_Error

0 for success, or an error code as defined in <devices/trackdisk.h>

CMD_WRITE