; vram_tile.asm -- PIXBLT B,XY: one 32x32 1-bpp dictionary tile to the screen.
;
; Task 4's tile primitive.  A dictionary entry is 32 rows of FOUR bytes (32 px
; is two 16-bit words) = 128 bytes = 1024 bits, row-major, LSB first within each
; byte (bit 0 is the leftmost pixel -- the scanout order) -- tilecost.py's
; layout.  PIXBLT's B source form reads packed 1-bit
; pixels from a linear bit address and writes an XY destination, so one tile is
;
;     SADDR = dict_base + index * 1024     (128 bytes a tile: index << 10)
;     SPTCH = 32                           (4 bytes a source row)
;     DADDR = (ty*32 << 16) | (tx*32)      (XY destination)
;     DYDX  = (32 << 16) | 32              (32 rows, 32 pixels)
;
;   DESCRIPTION-register assignments for PIXBLT B,XY (TMS34010 User's Guide,
;   instruction reference; vram.asm already uses the same values for L,XY and
;   vram_b.asm for B,XY):
;     SADDR   = B0   source bit address (1 bpp, packed)
;     SPTCH   = B1   source pitch in bits (4 bytes = 32 bits a row)
;     DADDR   = B2   destination XY: (y << 16) | x
;     DPTCH   = B3   destination pitch in bits (0x800 = 256-byte screen row)
;     OFFSET  = B4   VRAM base bit address
;     DYDX    = B7   dimensions in XY form: (rows << 16) | columns
;
;   COLOR0  = B8   pixel value for a clear source bit (0 = black)
;   COLOR1  = B9   pixel value for a set source bit (0xFFFF = white)
;
; B8/B9 are NOT I/O registers: they are implied operands of every graphics
; instruction, and a PIXBLT B expands a packed 1-bpp source into pixel values.
; They are set explicitly because the resident OS leaves them arbitrary --
; measured in the strip work: the first draw run painted every row black
; because nothing had set B9.  vram_b.asm's comment records the same finding.
;
;   PSIZE   (0C0000150h) 1     one bit per destination pixel
;   CONVSP  (0C0000130h) 14h   0x800-bit pitch code (1 << (~0x14 & 0x1F) = 2048)
;   CONVDP  (0C0000140h) 14h   same, for the XY destination
;   PMASK   (0C0000160h) 0     every plane writable
;   CONTROL (0C00000B0h)       raster op 0 (replace), CD/RM/RR preserved
;
; Entry point / calling form (ruling R13).  The TMS34010 C compiler's argument
; frame is not decoded by any hand-written assembly in this repository; the
; published-word form of vram.asm and vram_b.asm is used instead.  This symbol
; takes NO arguments: the two values a caller can change live in .bss words
;
;     tile_src    the source tile's bit address
;     tile_daddr  the destination XY word
;
; and the C wrapper tile_blit(src, tx, ty) is the only entry point.  B7 (DYDX)
; is the constant 32x32 this primitive exists for.
;
; Two entry points, split by what changes: tile_init_() programs the constants
; (pitch, offset, dimensions, colours, PSIZE/CONVSP/CONVDP/PMASK/CONTROL) once
; per frame, and tile_blit_() then only reloads SADDR and DADDR -- the two
; registers PIXBLT destroys -- before executing it.
;
; Revert note: this file is new in Task 4 and nothing else calls it.  To
; revert, delete it, the VRAMTILE entries in build-stream.sh and the
; tile_blit/paint_tiles code in vidstream.c; the strip path (vram_b.asm) does
; not reference any symbol defined here and is unaffected.  The disassembly
; this copies is vram_b.asm's, and its value table is quoted above from
; vram_b.asm rather than re-derived.
;
; This file does NOT define _vid_dint_/_vid_eint_: they live in vram_b.asm and
; both objects are linked, so a second definition would be a duplicate symbol.

	.ref	_tile_src
	.ref	_tile_daddr
	.text

; _tile_init_ -- program everything that does not vary between tiles.
;
; Spec 8.3's hoist, and it is worth real time in MAME: measured per-tile cost
; was ~0.36 ms against the unit's ~40 us, and the call did 11 I/O-register
; accesses plus 8 push/pop pairs for constants that never change.  The registers
; this sets -- PSIZE, CONVSP, CONVDP, PMASK, CONTROL and B1 (SPTCH), B3 (DPTCH),
; B4 (OFFSET), B7 (DYDX), B8 (COLOR0), B9 (COLOR1) -- survive PIXBLT (the
; user's guide marks only SADDR/DADDR and B10-B14 as changed), so once per
; frame is enough.
;
; B8/B9 are NOT I/O registers: they are implied operands of every graphics
; instruction, and the resident OS leaves them arbitrary -- measured in the
; strip work: the first draw run painted every row black because nothing had
; set B9.
	.globl	_tile_init_
_tile_init_:
	setf	32, 0, 1
	movi	020h, b1		; SPTCH = 32 bits = four bytes a tile row
	movi	800h, b3		; DPTCH = 2048 bits = 256-byte screen row
	movi	04000000h, b4		; OFFSET = VRAM base
	movi	0200020h, b7		; DYDX = (32 rows << 16) | 32 pixels
	clr	b8			; COLOR0 = 0 (black)
	movi	0FFFFh, b9		; COLOR1 = all planes set (white)

	movi	1, a1
	move	a1, @0C0000150h, 0	; PSIZE  = 1
	movi	14h, a1
	move	a1, @0C0000130h, 0	; CONVSP = pitch code for 0x800 bits
	move	a1, @0C0000140h, 0	; CONVDP
	clr	a1
	move	a1, @0C0000160h, 0	; PMASK  = 0 (all planes writable)
	move	a1, @0C0000170h, 0	; upper half, for forward compatibility

	; raster op 0 (replace), CD/RM/RR preserved
	move	@0C00000B0h, a1, 0	; CONTROL
	andi	0801Fh, a1
	move	a1, @0C00000B0h, 0
	move	@0C00000B0h, a1, 0	; read back: I/O writes are pipelined
	rets

; _tile_blit_ -- one 32x32 tile, everything already programmed.
;
; Only B0 (SADDR) and B2 (DADDR) vary, and PIXBLT destroys both, so those two
; are the only registers this saves and reloads.  tile_init_() must have run.
;
; Revert note: this file is new in Task 4 and nothing else calls it.  To
; revert, delete it, the VRAMTILE entries in build-stream.sh and the
; tile_blit/paint_tiles code in vidstream.c; the strip path (vram_b.asm) does
; not reference any symbol defined here and is unaffected.
	.globl	_tile_blit_
_tile_blit_:
	setf	32, 0, 1
	move	b0, -*sp, 1
	move	b2, -*sp, 1
	move	@_tile_src, b0, 1	; SADDR: dictionary entry, index << 10 bits
	move	@_tile_daddr, b2, 1	; DADDR (XY): (ty*32 << 16) | tx*32
	pixblt	b, xy
	move	*sp+, b2, 1
	move	*sp+, b0, 1
	rets

	.end