implemented BRK handling routine (not yet connected to IRQ)

2019-08-06 20:54:27 +02:00
1 parent 44ca73be40
commit 03bc8b8e78
@@ -1,3 +1,4 @@
+
 default_irq_handler:	

 	jsr blink_cursor
@@ -0,0 +1,8 @@
+All the Kernal routines, for which there are vectors in $0314-$0333, have to be available at their original addresses.
+
+Reason: some autostart software (https://codebase64.org/doku.php?id=base:autostarting_disk_files) override these vectors, so that some point
+to new locations (custom IRQ routine, custom STOP routine, etc.), while others points the original Kernal routines. Different techniques modify
+different vectors (while resetting others to original C64 locations), some don't change the vectors at all, but might still put the original
+C64 Kernal addresses there (for example, if the file overrides keyboard input buffer and screeen memory).
+
+For various cartridges (like IDE64) this just means disabling their extensions; for us that would mean improperly functionning Kernal.
@@ -0,0 +1,11 @@
+	;; https://csdb.dk/forums/index.php?roomid=11&topicid=5776
+	;; Clear the CIA1 interrupt flag, and then fall through to
+	;; the return from interrupt routine
+
+clear_cia1_interrupt_flag_and_return_from_interrupt:
+
+	;; We have free choice of LDA, LDX or LDY to achieve this goal
+	;; in 3 bytes and minimum cycles. Thus we randomly choose LDY.
+	LDY $DC0D
+
+	;; FALL THROUGH to $EA81
@@ -0,0 +1,18 @@
+	;; The IRQ is a commonly messed with thing on the C64,
+	;; so we need to handle entry points that are commonly
+	;; relied upon, including:
+	;; $EA31 - Standard IRQ routine
+	;; $EA61 - Check keyboard, but don't update timer? https://github.com/cc65/cc65/issues/324
+	;; $EA81 - https://www.lemon64.com/forum/viewtopic.php?t=2112&sid=6ea01982b26da69783120a7923ca46fb
+	;; Also the $0314 vector is widely used (e.g., https://www.lemon64.com/forum/viewtopic.php?t=2112&sid=6ea01982b26da69783120a7923ca46fb)
+
+return_from_interrupt:
+	;; Restore registers and return
+	;; Sequence according to Compute's Mapping the 64 p73
+	pla
+	tay
+	pla
+	tax
+	pla
+	rti
+	
@@ -1,7 +1,11 @@

 default_nmi_handler:

-	;; XXX provide real implementation
+	;; XXX implement according to Compute's Mapping the Commodore 64, page 74
+
+	;; XXX check if the source was RESTORE key, quit if it wasn't (no RS-232 support)
+	;; XXX if cartridge present, enter it through warm start vector
+	;; XXX if stop pressed, go to default_brk_handler

 	inc $D020
 	rti
@@ -0,0 +1,8 @@
+All the Kernal routines, for which there are vectors in $0314-$0333, have to be available at their original addresses.
+
+Reason: some autostart software (https://codebase64.org/doku.php?id=base:autostarting_disk_files) override these vectors, so that some point
+to new locations (custom IRQ routine, custom STOP routine, etc.), while others points the original Kernal routines. Different techniques modify
+different vectors (while resetting others to original C64 locations), some don't change the vectors at all, but might still put the original
+C64 Kernal addresses there (for example, if the file overrides keyboard input buffer and screeen memory).
+
+For various cartridges (like IDE64) this just means disabling their extensions; for us that would mean improperly functionning Kernal.
@@ -1,6 +1,11 @@
+
 default_brk_handler:

-	;; XXX implement this!
+	;; Implemented according to Compute's Mapping the Commodore 64, pages 73-74
+
+	jsr JRESTOR
+	jsr JIOINIT
+	jsr CINT_BRK
+
+	jmp (IBASIC_WARM_START)

-	;; Acknowledge CIA interrupt and return
-	jmp clear_cia1_interrupt_flag_and_return_from_interrupt
@@ -0,0 +1,8 @@
+All the Kernal routines, for which there are vectors in $0314-$0333, have to be available at their original addresses.
+
+Reason: some autostart software (https://codebase64.org/doku.php?id=base:autostarting_disk_files) override these vectors, so that some point
+to new locations (custom IRQ routine, custom STOP routine, etc.), while others points the original Kernal routines. Different techniques modify
+different vectors (while resetting others to original C64 locations), some don't change the vectors at all, but might still put the original
+C64 Kernal addresses there (for example, if the file overrides keyboard input buffer and screeen memory).
+
+For various cartridges (like IDE64) this just means disabling their extensions; for us that would mean improperly functionning Kernal.
@@ -1,3 +1,4 @@
+
 irq_handler:
 	;; The IRQ is a commonly messed with thing on the C64,
 	;; so we need to handle entry points that are commonly
@@ -7,17 +8,18 @@ irq_handler:
 	;; $EA81 - https://www.lemon64.com/forum/viewtopic.php?t=2112&sid=6ea01982b26da69783120a7923ca46fb
 	;; Also the $0314 vector is widely used (e.g., https://www.lemon64.com/forum/viewtopic.php?t=2112&sid=6ea01982b26da69783120a7923ca46fb)

-	;; Save registers
-	;; Sequence according to Compute's Mapping the 64 p73
+	;; Save registers, sequence according to Compute's Mapping the Commodore 64, page 73
 	pha
 	txa
 	pha
 	tya
 	pha

-	;; Call interrupt routine
-	;; (but only if initialised)
+	;; Call interrupt routine (only if initialised)
 	lda CINV
 	ora CINV+1
-	beq default_irq_handler
+	bne +
 	jmp (CINV)
+*
+	;; Vector not initialized - call default interrupt routine
+	jmp default_irq_handler
@@ -1,5 +1,7 @@

 nmi_handler:

+	;; XXX provide real implementation
+
 	jmp (NMINV)