added c64 test programs

c64testprgs/rasterIRQ.asm

@@ -0,0 +1,30 @@
+
+	*=$0801
+	.word (+), 2005
+	.null $9e, format("%d", start)
++	.word 0
+
+	* = 2084
+
+
+start
+	sei
+	lda  #$7f
+	sta  $dc0d
+	and  $d011
+	sta  $d011
+	lda  #123
+	sta  $d012
+	lda  #<irq
+	sta  $0314
+	lda  #>irq
+	sta  $0315
+	lda  #1
+	sta  $d01a
+	cli
+	rts
+
+irq
+	inc  $0400
+	asl  $d019
+	jmp  $ea31

c64testprgs/testTOD.asm

@@ -0,0 +1,134 @@
+	CIA1	= $DC00
+	CIA2	= $DD00
+	SCREEN	= $0400
+
+	*=$0801
+	.word (+), 2005
+	.null $9e, format("%d", start)
++	.word 0
+
+	* = 2084
+
+
+start
+	jsr  $e544	; clear screen
+	lda  CIA1+15
+	and  #%01111111
+	sta  CIA1+15
+	lda  CIA2+15
+	and  #%01111111
+	sta  CIA2+15
+
+	lda  #$08
+	sta  CIA1+11
+	lda  #$13
+	sta  CIA2+11
+	lda  #$59
+	sta  CIA1+10
+	lda  #$20
+	sta  CIA2+10
+	lda  #$50
+	sta  CIA1+9
+	lda  #$40
+	sta  CIA2+9
+	lda  #$00
+	sta  CIA1+8
+	sta  CIA2+8
+
+	lda  CIA1+8		; start TOD timer in CIA1
+	lda  CIA2+8		; start TOD timer in CIA2
+
+loop
+	lda  CIA1+8
+	ora  #'0'
+	sta  SCREEN+0
+
+	lda  CIA2+8
+	ora  #'0'
+	sta  SCREEN+0+40
+
+	lda  CIA1+9
+	tay
+	lsr  a
+	lsr  a
+	lsr  a
+	lsr  a
+	ora  #'0'
+	sta  SCREEN+2
+	tya
+	and  #$0f
+	ora  #'0'
+	sta  SCREEN+3
+
+	lda  CIA2+9
+	tay
+	lsr  a
+	lsr  a
+	lsr  a
+	lsr  a
+	ora  #'0'
+	sta  SCREEN+2+40
+	tya
+	and  #$0f
+	ora  #'0'
+	sta  SCREEN+3+40
+
+	lda  CIA1+10
+	tay
+	lsr  a
+	lsr  a
+	lsr  a
+	lsr  a
+	ora  #'0'
+	sta  SCREEN+5
+	tya
+	and  #$0f
+	ora  #'0'
+	sta  SCREEN+6
+
+	lda  CIA2+10
+	tay
+	lsr  a
+	lsr  a
+	lsr  a
+	lsr  a
+	ora  #'0'
+	sta  SCREEN+5+40
+	tya
+	and  #$0f
+	ora  #'0'
+	sta  SCREEN+6+40
+
+	lda  CIA1+11
+	tay
+	lsr  a
+	lsr  a
+	lsr  a
+	lsr  a
+	ora  #'0'
+	sta  SCREEN+8
+	tya
+	and  #$0f
+	ora  #'0'
+	sta  SCREEN+9
+
+	lda  CIA2+11
+	tay
+	lsr  a
+	lsr  a
+	lsr  a
+	lsr  a
+	ora  #'0'
+	sta  SCREEN+8+40
+	tya
+	and  #$0f
+	ora  #'0'
+	sta  SCREEN+9+40
+
+	jmp  loop
+
+
+
+
+
+

src/main/kotlin/razorvine/c64emu/Screen.kt

@@ -233,9 +233,11 @@ internal class Screen(private val chargenData: ByteArray, val ram: MemoryCompone
     private val coloredCharacterImageCache = mutableMapOf<Triple<Int, Int, Boolean>, BufferedImage>()
 
     private fun drawColoredChar(x: Int, y: Int, char: Int, color: Int, charsetAddr: Address) {
-        // The vic 'sees' the charset rom at these addresses: $1000 + $1800, $9000 + $9800
-        // so we can use pre-loaded images to efficiently draw the characters.
-        // If the address is different, the vic takes charset data from RAM instead.
+        // The vic 'sees' the charset ROM at these addresses: $1000(normal) + $1800(shifted), $9000(normal) + $9800(shifted)
+        // so we can use pre-loaded images to efficiently draw the default ROM characters.
+        // If the address is different, the vic takes charset data from RAM instead (thus allowing user defined charsets)
+        // A user-supplied character set in RAM must begin at an address that is 2048 byte aligned,
+        // and lies within the same 16K VIC bank as the screen character memory.
         // TODO: currently custom charsets taken from RAM aren't supported
         val shifted = charsetAddr and 0x0800 != 0
         val charImage = getCharImage(char, color, shifted)