more work on RAMTAS routine based on Compute's Mapping the 64

c64/kernal/,aliases.s

@@ -4,7 +4,6 @@
 ;	(https://www.c64-wiki.com/wiki/Zeropage)
 
 	.alias TXTTAB $2B
-	.alias MEMSIZ $37
 	.alias IOSTATUS $90
 	; Keys down clears bits. STOP=bit 7, C= bit 6, SPACE bit 4, CTRL bit 2
 	.alias BUCKYSTATUS $91
@@ -49,3 +48,15 @@
 	.alias rs232_tx_buffer_ptr $F9
 
 
+	; "Compute's Mapping the 64" book
+	.alias MEMSTR $0281
+	.alias MEMSIZ $0283 	; NOTE: Mapping the 64 erroniously has the hex as $282, while the DEC is correct
+	.alias text_colour $0286 ; p55
+	.alias colour_under_cursor $0287 ; p56
+	.alias HIBASE $0288     ; p56 (high byte of start of screen)
+	.alias key_buffer_size $0289 ; p57
+
+	;; 0 = cursor keys, insert, delete and space repeat, but nothing else
+	;; 128 = all keys repeat
+	;; 64 = no keys repeat
+	.alias key_repeat_flags $028A ; p58

c64/kernal/ramtas.s

@@ -1,7 +1,6 @@
 ; Function defined on pp272-273 of C64 Programmers Reference Guide
 ramtas:
 	; C64 Programmer's Reference guide p291:
-
 	; Clear $0000-$0101, $0200-$03ff
 	; PGS: $0000, $0001 are CPU IO ports, so shouldn't get written to
 	LDY #$02
@@ -17,6 +16,11 @@ ramtas_l2:
 	BNE ramtas_l2
 
 	; allocate cassette buffer
+	;; "Mapping the C128", p61
+	lda #<$033C
+	STA cassette_buffer_ptr+0
+	lda #>$033C
+	STA cassette_buffer_ptr+1
 
 	; set screen address to $0400
 	; https://www.c64-wiki.com/wiki/Screen_RAM
@@ -35,4 +39,32 @@ ramtas_l2:
 	ORA #$03
 	STA $DD00
 
+	;; Set screen address pointer ("Compute's Mapping the 64" p238)
+	LDA #>$0400
+	STA HIBASE
+	
+	;;  Work out RAM size and put in MEMSTR and MEMSIZ
+	;; "Compute's Mapping the 64", p54
+	lda #$00
+	sta MEMSTR+0
+	sta MEMSIZ+0
+	;; Try to modify $8000, if it fails then RAM ends at $7FFF, else $9FFF
+	lda $8000
+	eor #$FF
+	tax
+	eor #$FF
+	stx $8000
+	cmp $8000
+	bne ramtas_32K_RAM
+	sta $8000
+	lda #$A0
+	sta MEMSIZ+1
+	jmp ramtas_RAM_sized
+ramtas_32K_RAM:	
+	sta $8000 		; in case RAM is hiding beneath a ROM
+	lda #$80
+	sta MEMSIZ+1
+	;; Fall through
+ramtas_RAM_sized:	
+	
 	rts