From a974b4a763bb5805946a62fe7bbb321b7c98e01a Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Thu, 3 Sep 2020 20:28:38 +0200
Subject: [PATCH] added way to detect MEGA65 from the BASIC

---
 doc/Extended-BASIC.md                         |  4 ++
 src/basic/basic_commands/cmd_if.s             | 11 ++++
 .../basic_commands/helper_if_mega65_38K.s     | 52 ++++++++++++++++++
 .../basic_commands/helper_if_mega65_46K_50K.s | 54 +++++++++++++++++++
 4 files changed, 121 insertions(+)
 create mode 100644 src/basic/basic_commands/helper_if_mega65_38K.s
 create mode 100644 src/basic/basic_commands/helper_if_mega65_46K_50K.s

diff --git a/doc/Extended-BASIC.md b/doc/Extended-BASIC.md
index 44c31c97..3de5a66d 100644
--- a/doc/Extended-BASIC.md
+++ b/doc/Extended-BASIC.md
@@ -103,3 +103,7 @@ Same as `SYS`, but does not switch to C64 compatibility mode.
 ### `GO 64`, `GO 65` (MEGA65)
 
 Switches machine to C64 compatibility mode or to MEGA65 native mode. Performs `CLR`
+
+### `IF MEGA65 THEN`, `IF MEGA65 GOTO` (MEGA65)
+
+Special check for running under MEGA65. The `MEGA65` string is not tokenized, therefore it will be listed properly even under original BASIC V2. `MEGA65` is not a variable here - it is still possible to normally use the `ME` variable.
diff --git a/src/basic/basic_commands/cmd_if.s b/src/basic/basic_commands/cmd_if.s
index 1c52ad63..7e3a4488 100644
--- a/src/basic/basic_commands/cmd_if.s
+++ b/src/basic/basic_commands/cmd_if.s
@@ -5,6 +5,13 @@
 
 cmd_if:
 
+#if ROM_LAYOUT_M65
+
+	jsr helper_if_mega65
+	bcc cmd_if_true
+
+#endif
+
 	// Calculate expression
 
 	jsr FRMEVL
@@ -14,6 +21,10 @@ cmd_if:
 	lda FAC1_exponent
 	beq_16 cmd_rem
 
+	// FALLTROUGH
+
+cmd_if_true:
+
 	// Condition fulfilled - look for GOTO or THEN
 
 	jsr fetch_character_skip_spaces
diff --git a/src/basic/basic_commands/helper_if_mega65_38K.s b/src/basic/basic_commands/helper_if_mega65_38K.s
new file mode 100644
index 00000000..fd93f63e
--- /dev/null
+++ b/src/basic/basic_commands/helper_if_mega65_38K.s
@@ -0,0 +1,52 @@
+// #LAYOUT# M65 BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+#if CONFIG_MEMORY_MODEL_38K
+
+helper_if_mega65:
+
+	// Injest all spaces
+
+	ldy #$00
+!:
+	lda (TXTPTR), Y
+	cmp #$20
+	bne !+
+	inw TXTPTR
+	bra !-
+!:
+
+	// Check for MEGA65 untokenized keyword
+
+	ldy #$05
+!:
+	lda (TXTPTR), Y
+	cmp str_mega65, Y
+	bne_16 helper_if_mega65_fail
+	dey
+	bpl !-
+
+	// Increment TXTPTR by 6
+
+	clc
+	lda TXTPTR+0
+	adc #$06
+	sta TXTPTR+0
+	bcc !+
+	inc TXTPTR+1
+!:
+	// Report successful check
+
+	clc
+	rts
+
+helper_if_mega65_fail:
+
+	sec
+	rts
+
+str_mega65:
+
+	.byte $4D, $45, $47, $41, $36, $35
+
+#endif
diff --git a/src/basic/basic_commands/helper_if_mega65_46K_50K.s b/src/basic/basic_commands/helper_if_mega65_46K_50K.s
new file mode 100644
index 00000000..24b76024
--- /dev/null
+++ b/src/basic/basic_commands/helper_if_mega65_46K_50K.s
@@ -0,0 +1,54 @@
+// #LAYOUT# M65 BASIC_0 #TAKE-HIGH
+// #LAYOUT# *   *       #IGNORE
+
+// This has to go $E000 or above - routine below banks out the main BASIC ROM!
+
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+helper_if_mega65:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Injest all spaces
+
+	ldy #$00
+!:
+	lda (TXTPTR), Y
+	cmp #$20
+	bne !+
+	inw TXTPTR
+	bra !-
+!:
+
+	// Check for MEGA65 untokenized keyword
+
+	ldy #$05
+!:
+	lda (TXTPTR), Y
+	cmp str_mega65, Y
+	bne_16 remap_BASIC_sec_rts
+	dey
+	bpl !-
+
+	// Increment TXTPTR by 6
+
+	clc
+	lda TXTPTR+0
+	adc #$06
+	sta TXTPTR+0
+	bcc !+
+	inc TXTPTR+1
+!:
+	// Report successful check
+
+	jmp remap_BASIC_clc_rts
+
+str_mega65:
+
+	.byte $4D, $45, $47, $41, $36, $35
+
+
+#endif