Added VBLANK_INIT and VBLANK_HANDLER

Author: breakintoprogram

interrupts.asm

@@ -2,39 +2,77 @@
 ; Title:	BBC Basic for AGON - Interrupts
 ; Author:	Dean Belfield
 ; Created:	06/05/2022
-; Last Updated:	06/05/2022
+; Last Updated:	23/03/2023
 ;
 ; Modinfo:
+; 23/03/2023:		Added VBLANK_INIT and VBLANK_HANDLER
 
 			.ASSUME	ADL = 0
 				
+			INCLUDE	"macros.inc"
 			INCLUDE	"equs.inc"
+			INCLUDE "mos_api.inc"	; In MOS/src
 
 			SEGMENT CODE
 				
-			XDEF	INIT_IM2
-				
-; Initialise IM2
-; HL: Address of vector table (must be on page boundary)
-;
-INIT_IM2:		DI
-			LD	DE, INV_DUMMY
-			LD	L, 0
-$$:			LD	(HL), E
-			INC	L
-			LD	(HL), D
-			INC	L
-			JR	NZ, $B
-			LD	A, H
-			IM	2		; Set the interrupt mode
-			LD	I, A	
+			XDEF	VBLANK_INIT
+			XDEF	VBLANK_HANDLER	
+
+			XREF	ESCSET	
+			XREF	KEYDOWN		; In ram.asm
+			XREF	KEYASCII 	; In ram.asm
+
+; Hook into the MOS VBLANK interrupt
+;
+VBLANK_INIT:		DI
+			LD		E, 32h				; Set up the VBLANK interrupt
+			LD		HL, VBLANK_HANDLER	
+			MOSCALL		mos_setintvector
+			EX		DE, HL				; DEU: Address of previous interrupt handler
+			LD		HL, VBLANK_HANDLER_JP + 1	; This is a 16-bit address within this segment
+			LD		A, MB	 			; Get the current segment
+			CALL		SET_AHL16 			; Convert to an absolute 24-bit address
+			LD.LIL		(HL), DE			; Self-modify the code
+			EI	
 			RET
-				
-			.ASSUME ADL = 1
 
+; Set the MSB of HL (U) to A
+;
+SET_AHL16:		PUSH.LIL	HL
+			LD.LIL		HL, 2
+			ADD.LIL		HL, SP
+			LD.LIL		(HL), A
+			POP.LIL		HL
+			RET 
+
+; A safe LIS call to ESCSET
+; 
+DO_KEYBOARD:		MOSCALL		mos_sysvars			; Get the system variables
+			LD.LIL		A, (IX + sysvar_vkeydown)	; Fetch key down value (1 = key down, 0 = key up)
+			LD		(KEYDOWN), A 			; Store locally
+			OR		A 
+			JR		Z, $F 				; If it is key up, then skip to next bit
+			LD.LIL		A, (IX + sysvar_keyascii)	; Fetch key ASCII value
+$$:			LD		(KEYASCII), A 			; Store locally
+			CP		1Bh				; Is it escape?
+			CALL		Z, ESCSET			; Yes, so set the escape flags
+			RET.LIS						; Return to the interrupt handler
 
+;
 ; Interrupts in mixed mode always run in ADL mode
 ;
-INV_DUMMY:		EI
-			RETI.L
+			.ASSUME	ADL = 1
+
+VBLANK_HANDLER:		DI 
+			PUSH		AF 
+			PUSH		IX
+			CALL.LIS	DO_KEYBOARD
+			POP		IX 
+			POP		AF 
+;
+; Finally jump to the MOS interrupt
+;
+VBLANK_HANDLER_JP:	JP		0				; This is self-modified by VBLANK_INIT
+
+			.ASSUME	ADL = 0