Disk Device

Device Type: 0x96818B9A
Interrupt on completion: 0x72 (DiskOperationFinish) — read and write only
CLI Name: Disk

The disk device is a command-based serial device that reads and writes fixed-size blocks, and reports its capacity.

Block format

• Block size is 512 bytes.
• Operations are queued and executed serially.

Commands

Command	ID	Args
Read	1	3
Write	2	3
Get Size	3	0

Read and write both take:

1. VM memory address
2. start block
3. block count

Get size takes no arguments.

Read

Copies block count blocks from disk into VM memory starting at the provided memory address.

Write

Copies block count blocks from VM memory into disk starting at the provided block number.

Get Size

The next value the device emits from the serial protocol is the disk’s capacity in blocks, so the size in bytes is that value multiplied by 512. A disk whose length is not a whole number of blocks is reported rounded down, since a partial trailing block cannot be addressed.

Unlike read and write this is answered immediately and does not raise 0x72, so read the reply straight after issuing the command rather than waiting for the completion interrupt. It may be issued while a read or write is still in flight; it does not queue behind them.

Completion

After each read or write finishes, the device raises hardware interrupt 0x72. Get size is synchronous and never raises it.

Example

; Read 1 block from disk block 4 into memory at 0x200
OUT DISK_PORT, 1      ; Read
OUT DISK_PORT, 0x200  ; memory address
OUT DISK_PORT, 4      ; start block
OUT DISK_PORT, 1      ; block count

; Write 1 block from memory 0x200 to disk block 8
OUT DISK_PORT, 2      ; Write
OUT DISK_PORT, 0x200
OUT DISK_PORT, 8
OUT DISK_PORT, 1

; Ask the disk how big it is
OUT DISK_PORT, 3      ; Get Size
IN  r0, DISK_PORT     ; capacity in 512-byte blocks