native MEGA65 mode now runs with disabled hot registers (fixes IEC access)

src/aliases/,aliases_hardware_m65.s

@@ -20,6 +20,8 @@
 
 	.label VIC_CHARSTEP    = $D058 // 2 bytes  - logical characters per line
 
+	.label VIC_SRH         = $D05D //          - various flags, bit 7 = hot registers
+
 	.label VIC_SCRNPTR     = $D060 // 4 bytes  - pointer to start of screen memory
 	.label VIC_COLPTR      = $D064 // 2 bytes  - pointer to start of color memory
 

src/kernal/board_m65/mega65_imports.s

@@ -38,6 +38,8 @@
 .label viciv_unhide                    = KERNAL_0.viciv_unhide
 .label viciv_init                      = KERNAL_0.viciv_init
 .label viciv_shutdown                  = KERNAL_0.viciv_shutdown
+.label viciv_hotregs_on                = KERNAL_0.viciv_hotregs_on
+.label viciv_hotregs_off               = KERNAL_0.viciv_hotregs_off
 
 .label m65_scrtab_txtwidth             = KERNAL_0.m65_scrtab_txtwidth
 .label m65_scrtab_txtheight            = KERNAL_0.m65_scrtab_txtheight

src/kernal/board_m65/mega65_viciv_init.s

@@ -22,4 +22,21 @@ viciv_init:
 	lda #%01000000  // enable C65 character set
 	sta VIC_CTRLA
 
+	// Disable hot registers
+
+	// FALLTROUGH
+
+viciv_hotregs_off:
+
+	lda VIC_SRH
+	and #$7F
+!:
+	sta VIC_SRH
+	
 	rts
+
+viciv_hotregs_on:
+
+	lda VIC_SRH
+	ora #$80
+	bra !-

src/kernal/board_m65/mega65_viciv_shutdown.s

@@ -23,6 +23,10 @@ viciv_shutdown:
 	sta VIC_CTRLA  // enable C64 character set
 	sta VIC_CTRLB  // disable extended resolution and attributes
 
+	// Reenable hot registers
+
+	jsr viciv_hotregs_on
+
 	// Hide VIC-IV registers and quit
 
 	sta VIC_KEY

src/kernal/screen_m65/mega65_scrmodeset.s

@@ -46,11 +46,15 @@ m65_scrmodeset_internal: // entry point for M65_MODE65
 
 	tax
 
+	jsr viciv_hotregs_on
+
 	lda m65_scrtab_scrolx,x
 	sta VIC_SCROLX
 	lda m65_scrtab_vic_ctrlb,x
 	sta VIC_CTRLB
 
+	jsr viciv_hotregs_off
+
 	// Set the logical row length to 80
 
 	ldx #$50