collapseos/kernel/stdio.asm
Virgil Dupras 2a513e6f57 stdio: make stdioGetC and stdioReadline blocking
ref #64.

Also, fix a bug in the shell where it would write outside the buffer's
bounds when given a completely filled buffer without a space character
in it.
2019-11-03 20:32:27 -05:00

168 lines
3.3 KiB
NASM

; stdio
;
; Allows other modules to print to "standard out", and get data from "standard
; in", that is, the console through which the user is connected in a decoupled
; manner.
;
; Those GetC/PutC routines are hooked in during stdioInit and have this API:
;
; GetC: Blocks until a character is read from the device and return that
; character in A.
;
; PutC: Write character specified onto the device.
;
; *** Consts ***
; Size of the readline buffer. If a typed line reaches this size, the line is
; flushed immediately (same as pressing return).
.equ STDIO_BUFSIZE 0x20
; *** Variables ***
; Used to store formatted hex values just before printing it.
.equ STDIO_HEX_FMT STDIO_RAMSTART
.equ STDIO_GETC @+2
.equ STDIO_PUTC @+2
; Line buffer. We read types chars into this buffer until return is pressed
; This buffer is null-terminated.
.equ STDIO_BUF @+2
; Index where the next char will go in stdioGetC.
.equ STDIO_RAMEND @+STDIO_BUFSIZE
; Sets GetC to the routine where HL points to and PutC to DE.
stdioInit:
ld (STDIO_GETC), hl
ld (STDIO_PUTC), de
ret
stdioGetC:
ld ix, (STDIO_GETC)
jp (ix)
stdioPutC:
ld ix, (STDIO_PUTC)
jp (ix)
; print null-terminated string pointed to by HL
printstr:
push af
push hl
.loop:
ld a, (hl) ; load character to send
or a ; is it zero?
jr z, .end ; if yes, we're finished
call stdioPutC
inc hl
jr .loop
.end:
pop hl
pop af
ret
; print B characters from string that HL points to
printnstr:
push bc
push hl
.loop:
ld a, (hl) ; load character to send
call stdioPutC
inc hl
djnz .loop
.end:
pop hl
pop bc
ret
printcrlf:
push af
ld a, ASCII_CR
call stdioPutC
ld a, ASCII_LF
call stdioPutC
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
; Repeatedly calls stdioGetC until a whole line was read, that is, when CR or
; LF is read or if the buffer is full. Sets HL to the beginning of the read
; line, which is null-terminated.
;
; This routine also takes care of echoing received characters back to the TTY.
; It also manages backspaces properly.
stdioReadLine:
push bc
ld hl, STDIO_BUF
ld b, STDIO_BUFSIZE-1
.loop:
; Let's wait until something is typed.
call stdioGetC
; got it. Now, is it a CR or LF?
cp ASCII_CR
jr z, .complete ; char is CR? buffer complete!
cp ASCII_LF
jr z, .complete
cp ASCII_DEL
jr z, .delchr
cp ASCII_BS
jr z, .delchr
; Echo the received character right away so that we see what we type
call stdioPutC
; Ok, gotta add it do the buffer
ld (hl), a
inc hl
djnz .loop
; buffer overflow, complete line
.complete:
; The line in our buffer is complete.
; Let's null-terminate it and return.
xor a
ld (hl), a
ld hl, STDIO_BUF
pop bc
ret
.delchr:
; Deleting is a tricky business. We have to decrease HL and increase B
; so that everything stays consistent. We also have to make sure that
; We don't do buffer underflows.
ld a, b
cp STDIO_BUFSIZE-1
jr z, .loop ; beginning of line, nothing to delete
dec hl
inc b
; Char deleted in buffer, now send BS + space + BS for the terminal
; to clear its previous char
ld a, ASCII_BS
call stdioPutC
ld a, ' '
call stdioPutC
ld a, ASCII_BS
call stdioPutC
jr .loop