various Ultimate 64 improvements

src/basic/assets/startup_banner.s

@@ -16,7 +16,7 @@
 	!pet "open roms generic build"
 } else ifdef CONFIG_BRAND_TESTING {
 	!pet "open roms testing build"
-} else ifdef CONFIG_BRAND_ULTIMATE_64 {
+} else ifdef CONFIG_MB_U64 {
 	!pet "open roms for ultimate 64"
 }
 
@@ -43,9 +43,21 @@ rainbow_logo:
 	!set SET_COLOR_3 = $1E
 	!set SET_COLOR_4 = $9F
 
+!ifdef CONFIG_MB_U64 {
+
+	!byte SET_COLOR_1, $B8, $B8, $B8, $B8, $B8, $B8, $B8, $0D
+    !byte SET_COLOR_2, $B8, $B8, $B8, $B8, $B8, $B8, $B8, $0D
+    !byte SET_COLOR_3, $B8, $B8, $B8, $B8, $B8, $B8, $B8, $0D
+    !byte SET_COLOR_4, $B8, $B8, $B8, $B8, $B8, $B8, $B8, $0D
+    !byte SET_COLOR_0, $00
+
+} else {
+
 	!byte SET_COLOR_1, $12, $A4, $A4, $A4, $A4, $A4, $A4, $A4, $0D
     !byte SET_COLOR_2, $12, $A4, $A4, $A4, $A4, $A4, $A4, $0D
     !byte SET_COLOR_3, $12, $A4, $A4, $A4, $A4, $A4, $0D
     !byte SET_COLOR_4, $12, $A4, $A4, $A4, $A4, $92
     !byte SET_COLOR_0, $00
 }
+
+}

src/basic/basic_commands_01/cmd_fast_slow.s

@@ -9,17 +9,27 @@
 
 } else ifdef CONFIG_MB_U64 {
 
-	; Command implementation for Ultimate 64 - SuperCPU compatible way should be enough
+	; Command implementation for Ultimate 64
 
 cmd_slow:
 
-	sta SCPU_SPEED_NORMAL
+	lda #$00                           ; for U64_TURBOCTL - badlines, 1MHz
+	sta SCPU_SPEED_NORMAL              ; any value will do
+
+	; FALLTROUGH
+
+cmd_slow_fast_common:
+
+	sta U64_TURBOBIT                   ; only bit 0 matters
+	sta U64_TURBOCTL
 	rts
 
 cmd_fast:
 
-	sta SCPU_SPEED_TURBO
-	rts
+	lda #$0F                           ; for U64_TURBOCTL - badlines, 48MHz
+	sta SCPU_SPEED_TURBO               ; any value will do
+
+	bne cmd_slow_fast_common           ; bramnch always
 
 } else ifdef CONFIG_PLATFORM_COMMODORE_64 {