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kernel/zxspectrum/jumps.asm

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+; *** JUMP TABLE ***
+; include the addresses of the actual table into user.h for userspace utilities
+
+	jp	strncmp 
+	jp	upcase
+	jp	findchar
+	jp	parseHex
+	jp 	parseDecimal
+	jp	blkSel
+	jp	blkSet
+	jp	fsFindFN
+	jp	fsOpen
+	jp	fsGetB
+	jp	fsPutB
+	jp	fsSetSize
+	jp	fsOn
+	jp	fsIter
+	jp	fsAlloc
+	jp	fsHandle
+	jp	fsblkTell
+	jp	printstr
+	jp	printnstr
+	jp	printcrlf
+	jp	stdioPutC
+	jp	stdioGetC
+	jp	stdioReadLine
+	jp	_blkGetB
+	jp	_blkPutB
+	jp	_blkSeek
+	jp	_blkTell

kernel/zxspectrum/kbd.asm

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+; the ZX Spectrum BASIC firmware scans the keyboard for ASCII codes on clock interrupts
+; this routine just waits for a key and reads its value
+
+k_getc:
+;ei
+push hl
+ld hl, 23611 ; ZXS_FLAGS
+res 5, (hl)
+.loop:
+bit 5, (hl) ; pressed?
+jr z, .loop
+ld hl, 23560 ; ZXS_LASTK
+ld a, (hl)
+pop hl
+ret

kernel/zxspectrum/tapeblk.asm

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+; tape blkdev read-only
+; to be included as a kernel module.
+; In the glue.asm devices list the PutB pointer has to be unsetZ 
+
+; defines:
+; tap_buffer = 256-byte tape loading buffer in RAM
+; buf_pos = read position in the buffer
+; crossing the buffer boundaries require loading or rewinding+loading
+; tap_pos = previous read position of the block device,
+; then the difference btw current and previous positions, both in EDLH format as throughout the kernel code
+
+tapeblk_init:
+; initialized CFS and a placeholder 1-block, 1-byte file in the buffer
+; the tape fs is not default, has to be mounted
+ld hl, .plh
+ld de, tap_buffer
+ld bc, 6
+ldir
+ret
+.plh:
+.db "CFS",1,1,0,'@'
+
+tapeGetB:
+; it gets the new position in DE/HL, has to return value in A
+push bc
+push ix
+
+; First of all, is the difference between positions negative or positive?
+push hl ; store the position
+push de
+ld ix, tap_pos ; previous
+
+push de ; working copy, higher bytes
+ld e, (ix+2) ; lower bytes of previous position
+ld d, (ix+3)
+scf
+ccf
+sbc hl,de
+ld (ix+6), l
+ld (ix+7), h
+pop hl
+ld e, (ix+0) ; higher bytes
+ld d, (ix+1)
+sbc hl,de
+ld (ix+4), l
+ld (ix+5), h
+jp nc, .tblk_posdif
+
+.tblk_negdif:
+; at this point we have the negative difference
+pop de ; restore the current position
+pop hl
+; store it as 'the previous'
+ld (ix+0), e
+ld (ix+1), d
+ld (ix+2), l
+ld (ix+3), h
+
+; let's set the buffer position while we're here
+ld a, (buf_pos)
+add a, (ix+6) ; l
+; the difference bytes are negative, so e.g. add 255 = sub 1
+ld (buf_pos), a
+; no carry would mean underflow in this case
+jp nc, .tblk_rewind
+; we now have a chance that the higher bytes are FF (due to lower CY)
+xor a
+dec a
+and (ix+7)
+and (ix+4)
+and (ix+5)
+cp 255
+jp z, .tblk_readbyte ; a negative difference within the buffer
+
+; we have to rewind the tape and load back to the current position,
+; so it's safe to discard the difference and treat the current position as the positive difference
+
+.tblk_rewind:
+; as we will rewind to zero, at least one additional block is to be loaded
+xor a
+inc h
+cp h
+jr nz, .tblk_store
+inc de
+.tblk_store: 
+ld (ix+4), e ; diff
+ld (ix+5), d
+ld (ix+6), l ; diff
+ld (ix+7), h
+
+; purple border means 'rewind the tape and press enter'
+di
+ld a, 3
+out (254), a
+.tblk_key:
+ld a, 191  ; waiting for enter
+in a,(254)
+rra
+jr c, .tblk_key
+ei
+jr .tblk_skip
+; we don't have to set the buffer position, done it already
+
+.tblk_posdif:
+; at this point we have the difference and know it is positive
+pop de ; restore the current position
+pop hl
+; store it as 'the previous'
+ld (ix+0), e
+ld (ix+1), d
+ld (ix+2), l
+ld (ix+3), h
+
+.tblk_buffer:
+; setting the buffer position for the positive difference
+ld a, (buf_pos)
+add a, (ix+6) ; l
+ld (buf_pos), a
+jr nc, .tblk_skip
+
+; now we increase the higher difference bytes due to overflow
+xor a
+inc (ix+7) ; h
+cp (ix+7)
+jr nz, .tblk_skip
+inc (ix+4) ; e
+cp (ix+4)
+jr nz, .tblk_skip
+inc (ix+5) ; d 
+
+.tblk_skip:
+; Now, how many tape blocks do we have to load before the target block appears in the buffer?
+; it is shown by the 3 higher bytes of the difference
+; We've just set them up for the positive difference case.
+
+; For the negative difference case, the L-byte has to be equal to the buf_pos we set earlier
+
+; (ix+7) H, (ix+4) E, (ix+5) D is now the counter for blocks to be loaded
+; if it's 0, the block is already at the buffer and we don't have to load anything
+xor a
+or (ix+7)
+or (ix+4)
+or (ix+5)
+jp z, .tblk_readbyte
+
+; well, let's play the tape
+ld a, (ix+5)
+ld b,a ; this is the outer cycle
+inc b ; as we will djnz
+ld a, (ix+7)
+ld l, a ; lower byte of the inner counter
+ld a, (ix+4)
+ld h, a ; higher byte
+dec hl ; as we know at this point that at least one block is to be loaded
+ld c, 0 ; it's a 16-bit cycle flag used below
+xor a
+or h
+or l
+jp z, .tblk_load
+ld c, 1 ; hl=nonzero  
+
+.tblk_load:
+push bc ; counters
+push hl
+ld ix, tap_buffer ; we don't need the ix value anymore
+ld de, 256
+ld a, 255
+call t_load
+pop hl
+pop bc
+
+; counter
+xor a
+dec hl
+or h
+or l
+jr nz, .tblk_ccheck
+ld c, 0 ; on the next cycle, b has to be decremented
+jr .tblk_load
+.tblk_ccheck:
+xor a
+or c
+jp nz, .tblk_load
+inc c ; next 16-bit cycle
+djnz .tblk_load
+
+.tblk_readbyte:
+ld hl, tap_buffer
+ld b, 0
+ld a, (buf_pos)
+ld c, a
+add hl,bc
+ld a, (hl) ; here it is!
+pop ix
+pop bc
+cp a
+ret
+
+t_load:
+push iy
+ld iy, IYBAS
+scf
+; one can not call directly, as RST8 is then called upon break
+inc d
+ex af,af'
+dec d
+di
+ld a, 15
+out (254), a
+call 1378 ; jump into LD-BYTES
+t_ldret:
+ld a, (23624) ; restore border
+and 0x38
+rrca
+rrca
+rrca
+out (254),a
+pop iy
+ei
+ret
+
+;end

kernel/zxspectrum/vid.asm

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+v_init:
+call 3435 ; ZXS_CLS
+ld a, 2
+call 5633 ; ZXS_STRM, current stream = 1, main screen
+ret
+
+; the ZX Spectrum BASIC firmware puts the character in A into the current output stream by RST 16
+
+v_putc:
+; save all
+push hl
+push bc
+push de
+push af
+push ix
+push iy
+ld iy, IYBAS ; restore IY for BASIC
+; main
+push af ; char
+push bc ; curflag
+push de ; coords
+ld a, 22 ; AT_CTRL, screen position, 22x32
+rst 16
+pop de
+ld a, d
+push de
+rst 16
+pop de
+ld a, e
+rst 16
+pop bc
+xor a
+cp c
+jp z, .char
+ld a, 18 ; FLASH_CTRL
+rst 16
+xor a
+inc a ; on
+rst 16
+pop af
+rst 16
+ld a, 18 ; FLASH_CTRL
+rst 16
+xor a ; off
+rst 16
+jp .rest
+.char:
+pop af
+rst 16
+; restore and return
+.rest:
+pop iy
+pop ix
+pop af
+pop de
+pop bc
+pop hl
+ret