U64/JiffyDOS - do not blank screen if one can disable badlines

src/kernal/iec_fast/jiffydos_load.s

@@ -27,13 +27,30 @@ jiffydos_load:
 
 !ifdef CONFIG_IEC_JIFFYDOS_BLANK {
 
+!ifdef CONFIG_MB_U64 {
+
+	; Check if turbo register is available
+	lda U64_TURBOCTL
+	cmp #$FF
+	beq @1
+
+	; Store turbo register content, disable badlines
+	sta TBTCNT
+	lda #$80
+	sta U64_TURBOCTL
+	bne @2
+
+	; Normal flow - no turbo register
+}
+
+@1:
 	; Preserve register with screen status (blank/visible)
 	lda VIC_SCROLY
 	sta TBTCNT
 
 	; Blank screen to make sure no sprite/badline will interrupt
 	jsr screen_off
-
+@2:
 	; Preserve 3 lowest bits of CIA2_PRA  XXX deduplicate this
 
 	lda CIA2_PRA
@@ -42,9 +59,12 @@ jiffydos_load:
 
 } else {
 
+@1:
 	; Store previous sprite status in temporary variable
 	jsr jiffydos_prepare
 	sta TBTCNT
+@2:
+
 }
 
 	; A trick to shorten EAL update time
@@ -148,15 +168,34 @@ jiffydos_load_end:
 
 !ifdef CONFIG_IEC_JIFFYDOS_BLANK {
 
+!ifdef CONFIG_MB_U64 {
+
+	; Check if turbo register is available
+	lda U64_TURBOCTL
+	cmp #$FF
+	beq @3
+
+	; Restore turbo register content
+	lda TBTCNT
+	sta U64_TURBOCTL
+	jmp @4
+
+	; Normal flow - no turbo register
+}
+
+@3:
 	; Restore screen state
 	lda TBTCNT
 	sta VIC_SCROLY
+@4:
 
 } else {
 
+@3:
 	; Re-enable sprites
 	lda TBTCNT
 	sta VIC_SPENA
+@4:
 }
 
 	; Store last byte as unoptimized LOAD routine would