Release candidate 4

2025-10-31 11:56:44 -07:00 · 2020-07-25 01:06:56 -04:00
parent 50816d1499
commit 4df575bd62
4 changed files with 118 additions and 67 deletions
--- a/gsram_asm.s
+++ b/gsram_asm.s
@@ -0,0 +1,98 @@
+.setcpu		"65816"
+.autoimport on
+.importzp	sp
+
+.export 	_gsram_getsize
+
+.macro A8
+       sep #$20 ; put the 65C816 in 8-bit accumulator mode
+      .A8
+.endmacro
+
+.macro I8
+       sep #$10 ; put the 65C816 in 8-bit index register mode
+      .I8
+.endmacro
+
+.macro AI8
+       sep #$30 ; put the 65C816 in 8-bit accumulator and index register mode
+      .A8
+      .I8
+.endmacro
+
+.macro A16
+       rep #$20 ; put the 65C816 in 8-bit accumulator mode
+      .A16
+.endmacro
+
+.macro I16
+       rep #$10 ; put the 65C816 in 8-bit index register mode
+      .I16
+.endmacro
+
+.macro AI16
+       rep #$30 ; put the 65C816 in 8-bit accumulator and index register mode
+      .A16
+      .I16
+.endmacro
+
+.segment	"CODE"
+
+.proc _gsram_getsize: near
+.A8
+.I8
+	; Preamble
+	php				; Push status
+	sei				; Disable interrupts
+	clc				; Clear carry
+	xce				; Clear emulation bit
+	php				; Push status
+	phb				; Push bank
+	AI8
+
+	; Store bank number at address 0xFFFF in each bank
+	ldy #$7F		; Start at bank 0x7F
+	BankSetLoop:
+	phy				; Push future bank
+	plb 			; Pull bank
+	lda $8000		; Get address 0xFFFF in this bank
+	pha				; Save old address 0xFFFF contents
+	tya				; A = Y
+	eor #$FF		; Flip all bits
+	tay				; Y = A
+	sty $8000		; Overwrite address 0xFFFF with bank number
+	eor #$FF		; Flip all bits back
+	tay				; Y = A
+	dey				; Decrement bank number
+	cpy #$FF		; Have we wrapped around?
+	bne BankSetLoop ; If not, repeat
+
+	; Count banks with matching bank number
+	ldy #$00		; Y is bank
+	ldx #$00		; X is count
+	CountLoop:
+	phy				; Push future bank
+	plb				; Pull bank
+	tya				; A = Y
+	eor #$FF		; Flip all bits
+	tay				; Y = A
+	cpy $8000		; Is bank num stored at address 0xFFFF?
+	bne AfterInc	; If not, skip increment
+	inx				; If so, increment bank count
+	AfterInc:
+	eor #$FF		; Flip all bits back
+	tay				; Y = A
+	pla				; Get contents to restore
+	sta $8000		; Restore address 0xFFFF in this bank
+	iny				; Move to next bank
+	cpy #$80		; Are we at bank 0x80 yet?
+	bne CountLoop	; If not, repeat
+
+	; Postamble
+	plb				; Restore bank
+	plp				; Restore status
+	xce				; Restore emulation bit
+	txa				; Transfer bank count to A
+	plp				; Pull status again to pull I flag
+	rts
+.endproc