collapseos/apps/lib/stdio.asm
Virgil Dupras 019d05f64c Make the shell a userspace app
That's my mega-commit you've all been waiting for.

The code for the shell share more routines with userspace apps than with kernel
units, because, well, its behavior is that of a userspace app, not a device
driver.

This created a weird situation with libraries and jump tables. Some routine
belonging to the `kernel/` directory felt weird there.

And then comes `apps/basic`, which will likely share even more code with the
shell. I was seeing myself creating huge jump tables to reuse code from the
shell. It didn't feel right.

Moreover, we'll probably want basic-like apps to optionnally replace the shell.

So here I am with this huge change in the project structure. I didn't test all
recipes on hardware yet, I will do later. I might have broken some...

But now, the structure feels better and the line between what belongs to
`kernel` and what belongs to `apps` feels clearer.
2019-11-15 15:37:49 -05:00

71 lines
1.6 KiB
NASM

; *** Requirements ***
; printnstr
;
; *** Variables ***
; Used to store formatted hex values just before printing it.
.equ STDIO_HEX_FMT STDIO_RAMSTART
.equ STDIO_RAMEND @+2
; *** Code ***
; Format the lower nibble of A into a hex char and stores the result in A.
fmtHex:
; The idea here is that there's 7 characters between '9' and 'A'
; in the ASCII table, and so we add 7 if the digit is >9.
; daa is designed for using Binary Coded Decimal format, where each
; nibble represents a single base 10 digit. If a nibble has a value >9,
; it adds 6 to that nibble, carrying to the next nibble and bringing the
; value back between 0-9. This gives us 6 of that 7 we needed to add, so
; then we just condtionally set the carry and add that carry, along with
; a number that maps 0 to '0'. We also need the upper nibble to be a
; set value, and have the N, C and H flags clear.
or 0xf0
daa ; now a =0x50 + the original value + 0x06 if >= 0xfa
add a, 0xa0 ; cause a carry for the values that were >=0x0a
adc a, 0x40
ret
; Formats value in A into a string hex pair. Stores it in the memory location
; that HL points to. Does *not* add a null char at the end.
fmtHexPair:
push af
; let's start with the rightmost char
inc hl
call fmtHex
ld (hl), a
; and now with the leftmost
dec hl
pop af
push af
rra \ rra \ rra \ rra
call fmtHex
ld (hl), a
pop af
ret
; Print the hex char in A
printHex:
push bc
push hl
ld hl, STDIO_HEX_FMT
call fmtHexPair
ld b, 2
call printnstr
pop hl
pop bc
ret
; Print the hex pair in HL
printHexPair:
push af
ld a, h
call printHex
ld a, l
call printHex
pop af
ret