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149 lines
3.4 KiB
NASM
149 lines
3.4 KiB
NASM
; stdio
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;
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; Allows other modules to print to "standard out", and get data from "standard
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; in", that is, the console through which the user is connected in a decoupled
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; manner.
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;
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; Those GetC/PutC routines are hooked through defines and have this API:
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;
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; GetC: Blocks until a character is read from the device and return that
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; character in A.
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;
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; PutC: Write character specified in A onto the device.
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;
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; *** Accepted characters ***
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;
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; For now, we're in muddy waters in this regard. We try to stay close to ASCII.
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; Anything over 0x7f is undefined. Both CR and LF are interpreted as "line end".
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; Both BS and DEL mean "delete previous character".
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;
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; When outputting, newlines are marked by CR and LF. Outputting a character
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; deletion is made through BS then space then BS.
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;
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; *** Defines ***
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; STDIO_GETC: address of a GetC routine
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; STDIO_PUTC: address of a PutC routine
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;
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; *** Consts ***
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; Size of the readline buffer. If a typed line reaches this size, the line is
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; flushed immediately (same as pressing return).
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.equ STDIO_BUFSIZE 0x40
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; *** Variables ***
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; Line buffer. We read types chars into this buffer until return is pressed
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; This buffer is null-terminated.
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.equ STDIO_BUF STDIO_RAMSTART
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; Index where the next char will go in stdioGetC.
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.equ STDIO_RAMEND @+STDIO_BUFSIZE
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stdioGetC:
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jp STDIO_GETC
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stdioPutC:
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jp STDIO_PUTC
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; print null-terminated string pointed to by HL
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printstr:
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push af
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push hl
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.loop:
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ld a, (hl) ; load character to send
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or a ; is it zero?
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jr z, .end ; if yes, we're finished
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call STDIO_PUTC
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inc hl
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jr .loop
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.end:
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pop hl
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pop af
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ret
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; print B characters from string that HL points to
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printnstr:
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push bc
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push hl
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.loop:
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ld a, (hl) ; load character to send
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call STDIO_PUTC
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inc hl
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djnz .loop
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.end:
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pop hl
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pop bc
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ret
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; Prints a line terminator. This routine is a bit of a misnomer because it's
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; designed to be overridable to, for example, printlf, but we'll live with it
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; for now...
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printcrlf:
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push af
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ld a, CR
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call STDIO_PUTC
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ld a, LF
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call STDIO_PUTC
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pop af
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ret
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; Repeatedly calls stdioGetC until a whole line was read, that is, when CR or
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; LF is read or if the buffer is full. Sets HL to the beginning of the read
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; line, which is null-terminated.
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;
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; This routine also takes care of echoing received characters back to the TTY.
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; It also manages backspaces properly.
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stdioReadLine:
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push bc
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ld hl, STDIO_BUF
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ld b, STDIO_BUFSIZE-1
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.loop:
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; Let's wait until something is typed.
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call STDIO_GETC
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; got it. Now, is it a CR or LF?
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cp CR
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jr z, .complete ; char is CR? buffer complete!
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cp LF
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jr z, .complete
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cp DEL
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jr z, .delchr
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cp BS
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jr z, .delchr
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; Echo the received character right away so that we see what we type
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call STDIO_PUTC
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; Ok, gotta add it do the buffer
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ld (hl), a
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inc hl
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djnz .loop
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; buffer overflow, complete line
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.complete:
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; The line in our buffer is complete.
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; Let's null-terminate it and return.
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xor a
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ld (hl), a
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ld hl, STDIO_BUF
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pop bc
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ret
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.delchr:
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; Deleting is a tricky business. We have to decrease HL and increase B
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; so that everything stays consistent. We also have to make sure that
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; We don't do buffer underflows.
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ld a, b
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cp STDIO_BUFSIZE-1
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jr z, .loop ; beginning of line, nothing to delete
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dec hl
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inc b
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; Char deleted in buffer, now send BS + space + BS for the terminal
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; to clear its previous char
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ld a, BS
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call STDIO_PUTC
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ld a, ' '
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call STDIO_PUTC
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ld a, BS
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call STDIO_PUTC
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jr .loop
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