set IRQ frequency depending on video system

STATUS.md

@@ -27,8 +27,7 @@ The following ROM features are currently missing:
 * tape support
 * RS-232 support
 * breaking Kernal routines with RUN/STOP key
-* BRK handling
+* BRK handling; NMI/IRQ handling is incomplete
-* PAL/NTSC is detected, but for now only startup banner uses the result
 
 Features currently being worked on:
 
@@ -73,7 +72,7 @@ NOTE: Even the 'DONE' routines won't support features described as missing in on
 | Address   | Name     | Status   |  Remarks                                           |
 | --------- | :------- | :------: | :------------------------------------------------: |
 | `$FF81`   | `CINT`   | DONE     |                                                    |
-| `$FF84`   | `IOINIT` | DONE     |                                                    |
+| `$FF84`   | `IOINIT` | PARTIAL  | CIA initialization incomplete                      |
 | `$FF87`   | `RAMTAS` | DONE     |                                                    |
 | `$FF8A`   | `RESTOR` | DONE     |                                                    |
 | `$FF8D`   | `VECTOR` | DONE     |                                                    |

c64/kernal/cint.s

@@ -14,31 +14,7 @@ cint:
 cint_brk: ; entry for BRK and STOP+RESTORE - XXX, where should it start?
 
 	jsr setup_vicii
-
+	jsr setup_pal_ntsc
-	;; Detect video system (PAL/NTSC), use Graham's method, as it's short and reliable
-	;; see here: https://codebase64.org/doku.php?id=base:detect_pal_ntsc
-
-cint_w0:
-	lda VIC_RASTER
-cint_w1:
-	cmp VIC_RASTER
-    beq cint_w1
-    bmi cint_w0
-
-	;; Result in A, if no interrupt happened during the test:
-	;; #$37 -> 312 rasterlines, PAL,  VIC 6569
-	;; #$06 -> 263 rasterlines, NTSC, VIC 6567R8
-	;; #$05 -> 262 rasterlines, NTSC, VIC 6567R56A
-
-	cmp #$07
-	bcs cint_pal
-cint_ntsc:
-	lda #$00
-	beq +
-cint_pal:
-	lda #$01
-*
-	sta PALNTSC
 
 	;; Initialise cursor blink flags  (Compute's Mapping the 64 p215)
 	lda #$00

c64/kernal/fda3.ioinit.s

@@ -34,35 +34,54 @@ ioinit:
 	cpy #$80 ; $20 * amount of chips to silence, $80 to silence 4 chips
 	bne -
 
-	;; Enable CIA1 IRQ and ~50Hz timer
+	;; XXX: calibrate TOD for both CIA's, see here: https://codebase64.org/doku.php?id=base:efficient_tod_initialisation
-	;; (https://csdb.dk/forums/?roomid=11&topicid=69037)
+
-	lda #$7f
+	;; Enable CIA1 IRQ and ~50Hz timer (https://csdb.dk/forums/?roomid=11&topicid=69037)
-	sta $DC0D 		; First disable all
+	lda #$7F
+	sta CIA1_ICR ; disable all
 
 	;; Set timer interval to ~1/60th of a second
-	;; (This value was calculated by running a custom IRQ haandler on a C64
+	jsr setup_pal_ntsc
+	
+	;; (This value was calculated by running a custom IRQ handler on a C64
 	;; with original KERNAL, and writing the values of $DC04/5 to the screen
 	;; in the IRQ handler to see roughly what value the timers must be set to)
-	lda #<16380
+	;; ldy #<16380
-	sta $dc04
+	;; ldx #>16380
-	lda #>16380
+
-	sta $dc05
+	;; PAL C64 (https://codebase64.org/doku.php?id=base:cpu_clocking),
+	;; is clocked at 0.985248 MHz, so that 1/60s is 16421 CPU cycles
+
+	ldy #<16421
+	ldx #>16421
+
+	lda PALNTSC
+	bne +
+
+	;; NTSC C64 (https://codebase64.org/doku.php?id=base:cpu_clocking),
+	;; is clocked at 1.022727 MHz, so that 1/60s is 17045 CPU cycles
+
+	ldy #<17045
+	ldx #>17045
+
+	;; Store the IRQ timing constant to CIA chip
+*
+	sty CIA1_TIMALO
+	stx CIA1_TIMAHI
 
 	;; Enable timer interrupt
 	lda #$81
-	sta $dc0d
+	sta CIA1_ICR
 
-	;; Enable timer A to run continuously
+	;; Enable timer A to run continuously (http://codebase64.org/doku.php?id=base:timerinterrupts)
-	;; (http://codebase64.org/doku.php?id=base:timerinterrupts)
 	lda #$11
-	sta $dc0e
+	sta CIA1_CRA
-	lda $dc0d
+	lda CIA1_ICR
 
 	;; Set DDR on CIA2 for IEC bus, VIC-II banking
-	lda #$3b
+	lda #$3B
-	sta $dd02
+	sta CIA2_DDRA
 
-	;; Set IEC bus oto its initial idle state
+	;; Set IEC bus to its initial idle state
-	jsr iec_set_idle
+	jmp iec_set_idle
 
-	rts

c64/kernal/iec/iec_wait20us.s

@@ -6,7 +6,7 @@ iec_wait20us:
 	;; PAL:
 	;; - CPU frequency 0.985248 MHz, we need to waste at least 20 cycles
 	;; NTSC:
-	;; - CPU frequency 1.022727 MHZ, we need to waste at least 21 cycles
+	;; - CPU frequency 1.022727 MHz, we need to waste at least 21 cycles
 
 	;; Waste cycles by reading some unimportant memory location
 	;; in order not to clutter VICE debug logs

c64/kernal/iec/iec_wait60us.s

@@ -6,7 +6,7 @@ iec_wait60us:
 	;; PAL:
 	;; - CPU frequency 0.985248 MHz, we need to waste at least 60 cycles
 	;; NTSC:
-	;; - CPU frequency 1.022727 MHZ, we need to waste at least 62 cycles
+	;; - CPU frequency 1.022727 MHz, we need to waste at least 62 cycles
 
 	;; Waste cycles in a loop
 

c64/kernal/interrupts/fe47.default_nmi_handler.s

@@ -13,6 +13,8 @@ default_nmi_handler:
 
 	;; XXX: RS-232 support is not implemented
 
+	;; XXX confirm NMIs from CIA, or no other NMI will arrive!
+
 	jsr cartridge_check
 	bcc +
 	jmp (ICART_WARM_START)

c64/kernal/setup_pal_ntsc.s

@@ -0,0 +1,31 @@
+
+;;
+;; Detect video system (PAL/NTSC), use Graham's method, as it's short and reliable
+;; see here: https://codebase64.org/doku.php?id=base:detect_pal_ntsc
+;;
+
+setup_pal_ntsc:
+
+	lda VIC_RASTER
+setup_pal_ntsc_w1:
+	cmp VIC_RASTER
+	beq setup_pal_ntsc_w1
+	bmi setup_pal_ntsc
+
+	;; Result in A, if no interrupt happened during the test:
+	;; #$37 -> 312 rasterlines, PAL,  VIC 6569
+	;; #$06 -> 263 rasterlines, NTSC, VIC 6567R8
+	;; #$05 -> 262 rasterlines, NTSC, VIC 6567R56A
+
+	cmp #$07
+	bcs setup_pal
+
+setup_ntsc:
+	lda #$00
+	beq +
+
+setup_pal:
+	lda #$01
+*
+	sta PALNTSC
+	rts