
2.1.3 Hard Disk Implementation

The pseudo hard disks are implemented by the following two messages to read & write a specific logical sector number on a given drive.

2.1.3.1 Read Sector Message

Byte 0 .. 2   : $AA,$FF,$FF      Message Header
Byte 3        : $17              Read Sector message id
Byte 4        : $05              Byte count
Byte 5        : Drive            Drive number
Byte 6 .. 9   : LSN              Logical Sector no.

Status Message:

Byte 0 .. 2   : $AA,$FF,$FF      Message Header
Byte 3        : Status byte
Byte 4 .. n   : Sector data

This message requests the specified sector according to the LSN supplied from the secified drive. The Logical Sector Number specifies the sector number on the shared hard drive number from 0 to a possible 2^24-1. Up to 256 drives are theorhetically possible.

The PCRSS will first transfer a status byte (see para 2.1.2.1.14 for status byte definitions), and if is ok the sector data will then follow. The amount of data transferred depends on the sector size configuration defined when the PCRSS is setup.

2.1.3.2 Write Sector Message

Byte 0 .. 2   : $AA,$FF,$FF      Message Header
Byte 3        : $18              Write Sector message id
Byte 4        : $05              Byte count
Byte 5        : Drive            Drive number
Byte 6 .. 9   : LSN              Logical Sector no.
Byte 10.. n   : sector data

Status Message:

Byte 0 .. 2   : $AA,$FF,$FF      Message Header
Byte 3        : Status byte

Upon receiving this message, the PCRSS will transfer the sector data to the LSN specified on the shared hard drive specified and return a single status byte indicating the status of the transfer.


