; vram.asm -- hardware framebuffer fill for the VT1200 payload.
;
; The C loop in lance_cmd.c writes the screen one byte at a time and measures
; ~2.0 s per 1280x1024 frame (0.5 fps).  FILL L does the same job in the GSP's
; array engine: the manual's Table 13-6 gives (1 + N*G)L states for a long row,
; with G=2 for "replace, no plane masking", N=80 words/row and L=1024 rows --
; about 165k states, i.e. ~16 ms at a 10 MHz state, roughly 120x faster.
;
; Implied operands of FILL L (TMS34010 User's Guide, instruction reference):
;   DADDR  = B2   linear address of the first pixel of the array
;   DPTCH  = B3   pitch between rows, in bits
;   DYDX   = B7   dimensions in XY form: (rows << 16) | columns
;   COLOR1 = B9   fill colour / 16-bit pattern
;   CONTROL (0C00000B0h)  bits 10-14 PPOP = 0 -> replace (S -> D)
;   PSIZE   (0C0000150h)  1 -> one bit per pixel
;   PMASK   (0C0000160h)  0 -> no plane protected, all bits writable
;
; DADDR and DYDX are modified by the instruction, so they are reloaded on every
; call.  The pattern is read from the C global _vram_pattern (a .bss word) so
; no calling-convention assumption is needed.

	.ref	_vram_pattern
	.text
	.globl	_vram_fill_
_vram_fill_:
	setf	32, 0, 1
	move	b2, -*sp, 1
	move	b3, -*sp, 1
	move	b7, -*sp, 1
	move	b9, -*sp, 1

	; --- destination array -------------------------------------------------
	movi	04000000h, b2		; VRAM base, bit address
	movi	800h, b3		; 2048 bits = 256-byte row pitch
	movi	04000500h, b7		; DY=1024 (0400h), DX=1280 (0500h)
	move	@_vram_pattern, b9, 1	; fill pattern

	; --- pixel format ------------------------------------------------------
	movi	1, a1
	move	a1, @0C0000150h, 0	; PSIZE  = 1
	clr	a1
	move	a1, @0C0000160h, 0	; PMASK  = 0 (all planes writable)
	move	a1, @0C0000170h, 0	; upper half, for forward compatibility

	; --- graphics operation: replace, no transparency, no window ----------
	move	@0C00000B0h, a1, 0	; CONTROL
	andi	0801Fh, a1		; keep CD (15) and RM/RR (2-4) only
	move	a1, @0C00000B0h, 0
	move	@0C00000B0h, a1, 0	; read back: I/O writes are pipelined

	fill	l

	move	*sp+, b9, 1
	move	*sp+, b7, 1
	move	*sp+, b3, 1
	move	*sp+, b2, 1
	rets

	.end