mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-27 18:48:05 +11:00
92 lines
2.7 KiB
Markdown
92 lines
2.7 KiB
Markdown
# Using block devices
|
|
|
|
The `blockdev.asm` part manage what we call "block devices", an abstraction over
|
|
something that we can read a byte to, write a byte to and seek into (select at
|
|
which offset we will read/write to next).
|
|
|
|
A Collapse OS system can define up to `0xff` devices. Those definitions are made
|
|
in the glue code, so they are static.
|
|
|
|
Definition of block devices happen at include time. It would look like:
|
|
|
|
[...]
|
|
BLOCKDEV_COUNT .equ 1
|
|
#include "blockdev.asm"
|
|
; List of devices
|
|
.dw aciaGetC, aciaPutC, 0
|
|
[...]
|
|
|
|
That tells `blockdev` that we're going to set up one device, that its GetC and
|
|
PutC are the ones defined by `acia.asm` and that it has no Seek.
|
|
|
|
blockdev routines defined as zero are dummies (we don't actually call `0x0000`).
|
|
|
|
## Routine definitions
|
|
|
|
Parts that implement GetC, PutC and Seek do so in a loosely-coupled manner, but
|
|
they should try to adhere to the convention, that is:
|
|
|
|
**GetC**: Get a character at current position, advance the position by 1, then
|
|
return the fetched character in register `A`. If no input is
|
|
available, block until it is (in other words, we always get a valid
|
|
character).
|
|
|
|
**PutC**: The opposite of GetC. Write the character in `A` at current position
|
|
and advance. If it can't write, block until it can.
|
|
|
|
**Seek**: Set current position (word) to value in register `HL`.
|
|
|
|
## Shell usage
|
|
|
|
`blockdev.asm` supplies 2 shell commands that you can graft to your shell thus:
|
|
|
|
[...]
|
|
SHELL_EXTRA_CMD_COUNT .equ 2
|
|
#include "shell.asm"
|
|
; extra commands
|
|
.dw blkBselCmd, blkSeekCmd
|
|
[...]
|
|
|
|
### bsel
|
|
|
|
`bsel` select the active block device. For now, this only affects `load`. It
|
|
receives one argument, the device index. `bsel 0` selects the first defined
|
|
device, `bsel 1`, the second, etc. Error `0x04` when argument is out of bounds.
|
|
|
|
### seek
|
|
|
|
`seek` receives one word argument and sets the pointer for the currently active
|
|
device to the specified address. Example: `seek 1234`.
|
|
|
|
The device position is device-specific: if you seek on a device, then switch
|
|
to another device and seek again, your previous position isn't lost. You will
|
|
still be on the same position when you come back.
|
|
|
|
### Example
|
|
|
|
Let's try an example: You glue yourself a Collapse OS with ACIA as its first
|
|
device and a mmap starting at `0xd000` as your second device. Here's what you
|
|
could do to copy memory around:
|
|
|
|
> mptr d000
|
|
D000
|
|
> load 4 [device 0 is selected initially]
|
|
[enter "abcd"]
|
|
> peek 4
|
|
61626364
|
|
> mptr c000
|
|
C000
|
|
> peek 4
|
|
[RAM garbage]
|
|
> bsel 1
|
|
> load 4
|
|
[returns immediately]
|
|
> peek 4
|
|
61626364
|
|
> seek 0002
|
|
> load 2
|
|
> peek 4
|
|
63646364
|
|
|
|
Awesome, right?
|