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https://github.com/meithecatte/ember
an Apple II-style monitor that fits in your MBR.
https://github.com/meithecatte/ember
Last synced: 25 days ago
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an Apple II-style monitor that fits in your MBR.
- Host: GitHub
- URL: https://github.com/meithecatte/ember
- Owner: meithecatte
- License: mit
- Created: 2019-06-23T12:15:59.000Z (over 5 years ago)
- Default Branch: master
- Last Pushed: 2021-03-04T14:14:44.000Z (almost 4 years ago)
- Last Synced: 2024-05-01T15:15:46.736Z (8 months ago)
- Language: Assembly
- Size: 23.4 KB
- Stars: 9
- Watchers: 4
- Forks: 5
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# ember
An Apple II-style monitor that fits in your MBR.
# Usage
The ember monitor will prompt you with `>` once ready.
## Reading memory
Enter a 4-hexdigit lowercase address to view a hexdump of 16 bytes at that address:
```
>7c00
7c00: ea 0d 7c 00 00 47 7d 69 7d 12 7d 0b 7d fa 31 c9
>
```
It's also possible to specify a range with `.`:
```
>7c00.7c40
7c00: ea 0d 7c 00 00 47 7d 69 7d 12 7d 0b 7d fa 31 c9
7c10: 8e d9 8e c1 8e d1 bc 00 7c 88 16 37 7d fb fc bf
7c20: 80 00 be 05 7c b1 08 a5 31 c0 ab e2 fa 31 db b0
7c30: 3e cd 21 cd 20 be 00 06 e8 8b 00 72 05 93 89 df
>
```
The count is rounded up to the nearest 16 bytes:
```
>7c08.7c40
7c08: 7d 12 7d 0b 7d fa 31 c9 8e d9 8e c1 8e d1 bc 00
7c18: 7c 88 16 37 7d fb fc bf 80 00 be 05 7c b1 08 a5
7c28: 31 c0 ab e2 fa 31 db b0 3e cd 21 cd 20 be 00 06
7c38: e8 8b 00 72 05 93 89 df eb 03 be 00 06 ac 08 c0
>
```
## Writing memory
After the address, type a `:` and the bytes you want to poke:
```
>7e00:dead beef
>7e00
7e00: de ad be ef 00 00 00 00 00 00 00 00 00 00 00 00
>
```
## Inferred locations
Ember keeps track of the last read and write location and substitutes them
when you omit the address at the start of the line.
- The "read location" points after the last byte of the last read and is the default for
read operations:
```
>7c00
7c00: ea 0d 7c 00 00 47 7d 69 7d 12 7d 0b 7d fa 31 c9
>
7c10: 8e d9 8e c1 8e d1 bc 00 7c 88 16 37 7d fb fc bf
>
7c20: 80 00 be 05 7c b1 08 a5 31 c0 ab e2 fa 31 db b0
>.7c60
7c30: 3e cd 21 cd 20 be 00 06 e8 8b 00 72 05 93 89 df
7c40: eb 03 be 00 06 ac 08 c0 75 05 b9 01 00 eb 16 3c
7c50: 2e 75 39 e8 70 00 72 5f 29 d8 83 c0 0f c1 e8 04
>
```
- The "write location" points after the last byte of the last write and is the default for
write operations:
```
>7e00:cafe
>:babe
>7e00
7e00: ca fe ba be 00 00 00 00 00 00 00 00 00 00 00 00
>
```
- Specifying an explicit address moves both locations to that address:
```
>7c00
7c00: ea 0d 7c 00 00 47 7d 69 7d 12 7d 0b 7d fa 31 c9
>7e00:12 34 56 78
>
7e00: 12 34 56 78 00 00 00 00 00 00 00 00 00 00 00 00
>7e80
7e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>:abcd
>7e80
7e80: ab cd 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>
```
- Writes move the read location to the beginning of the write:
```
>7e80
7e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>:abcd
>
7e80: ab cd 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>
```
## Running code
The `g` command will call the specified address. When no address is provided, the write location
is used.
```
>7e00:4869210d00
>:be007e
>:ac 08c0 7404 cd21 ebf7 c3
>7e05g
Hi!
>
```
# Routines provided to runnning programs
Some routines used in ember are exposed as interrupts. Apart from explicit outputs, no registers
are modified.
```asm
; Interrupt 0x20
; Read a line of text and store it in the global `linebuffer` (0x600). The result is
; null-terminated. No overflow checking is performed.
; Interrupt 0x21
; Put a character on the screen. Expands \r into \r\n because the latter is required
; by the BIOS for a proper newline. \r is used to signify newlines because that's what
; the keyboard gives us.
; Input:
; AL = ASCII character
; Interrupt 0x22
; Read sector on the boot disk
; Input:
; eax = LBA
; es:di = operation buffer
; Stops execution on error
; Interrupt 0x23
; Write sector on the boot disk
; Input:
; eax = LBA
; es:di = operation buffer
```
# Limitations
- uppercase letters are not recognized in commands
- only the first 64K of memory is accessible
- the error handling creates confusing messages when less than
four hexdigits of address are provided
- backspacing over the edge of the screen desyncs what's visible from the internal buffer
# TODO
- `r` and `w` commands for accessing the boot disk.
- Restart the main loop after a disk error.