From e68d231ff6bbea90a39f3707a1308b113dccbb1c Mon Sep 17 00:00:00 2001
From: user <none>
Date: Fri, 1 Sep 2023 04:43:42 -0500
Subject: [PATCH] Add DDIR digital port direction instruction

This should be useful for switching between output and pull-up input,
which can be useful for scanning switch matrices.
---
 asm_2/bytecode.txt |  8 ++++----
 asm_2/interp.asm   | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 asm_2/tbc.inc      | 14 ++++++++++++--
 3 files changed, 60 insertions(+), 7 deletions(-)

diff --git a/asm_2/bytecode.txt b/asm_2/bytecode.txt
index 08eb179..69069c6 100644
--- a/asm_2/bytecode.txt
+++ b/asm_2/bytecode.txt
@@ -67,10 +67,10 @@ FXYN
 2XY5	shra
 2XY6	rol
 2XY7	ror
-2XY8
-2XY9	spi
-2XYA	mft
-2XYB	mtt
+2XY8	spi
+2XY9	mft
+2XYA	mtt
+2XYB	ddir
 2XYC	din
 2XYD	dout
 2XYE	ain
diff --git a/asm_2/interp.asm b/asm_2/interp.asm
index 8ad4d7f..6589817 100644
--- a/asm_2/interp.asm
+++ b/asm_2/interp.asm
@@ -542,10 +542,10 @@ imm4_dispatch_jumptable:
 	rjmp	exec_shra
 	rjmp	exec_rol
 	rjmp	exec_ror
-	rjmp	exec_nop
 	rjmp	exec_spi
 	rjmp	exec_mft
 	rjmp	exec_mtt
+	rjmp	exec_ddir
 	rjmp	exec_din
 	rjmp	exec_dout
 	rjmp	exec_ain
@@ -1343,6 +1343,49 @@ exec_mtt:
 	rjmp	_dispatch_done
 
 
+exec_ddir:
+	; Restrict operand to 0-f
+	ldi	r25, 0x0f
+	and	r10, r25
+
+	; Extract LSB from first operand
+	ldi	r23, 0x01
+	and	r6, r23
+	clr	r7
+
+	; Mask of all bits except LSB
+	ldi	r24, 0xfe
+	ldi	r25, 0xff
+
+	; Rotate LSB and mask into position specified by second operand
+_ddir_loop:
+	dec	r10
+	brlt	_din_loop_done
+
+	sec
+	rol	r24
+	rol	r25
+
+	clc
+	rol	r6
+	rol	r7
+
+	rjmp	_ddir_loop
+_ddir_loop_done:
+
+	; Read-modify-write
+	in	r22, DDRB
+	in	r23, DDRC
+	and	r22, r24
+	and	r23, r25
+	or	r22, r6
+	or	r23, r7
+	out	DDRB, r22
+	out	DDRC, r23
+
+	rjmp	_dispatch_done
+
+
 exec_din:
 	; Restrict operand to 0-f
 	ldi	r25, 0x0f
diff --git a/asm_2/tbc.inc b/asm_2/tbc.inc
index d0898c1..4035615 100644
--- a/asm_2/tbc.inc
+++ b/asm_2/tbc.inc
@@ -483,7 +483,7 @@
 	.if @1 < 1 || @1 > 0x10
 	.error "Tortoise Bytecode: SPI immediate value outside 4-bit range"
 	.endif
-	.dw	(0x2 << 12) | (@0 << 8) | ((@1 & 0xf) << 4) | (0x9)
+	.dw	(0x2 << 12) | (@0 << 8) | ((@1 & 0xf) << 4) | (0x8)
 .endmacro
 
 .macro T_MFT
@@ -493,10 +493,20 @@
 	.if @1 < 0 || @1 > 0xf
 	.error "Tortoise Bytecode: immediate value outside 4-bit range"
 	.endif
-	.dw	(0x2 << 12) | (@0 << 8) | (@1 << 4) | (0xa)
+	.dw	(0x2 << 12) | (@0 << 8) | (@1 << 4) | (0x9)
 .endmacro
 
 .macro T_MTT
+	.if @0 < 0 || @0 > 0xf
+	.error "Tortoise Bytecode: invalid variable register"
+	.endif
+	.if @1 < 0 || @1 > 0xf
+	.error "Tortoise Bytecode: immediate value outside 4-bit range"
+	.endif
+	.dw	(0x2 << 12) | (@0 << 8) | (@1 << 4) | (0xa)
+.endmacro
+
+.macro T_DDIR
 	.if @0 < 0 || @0 > 0xf
 	.error "Tortoise Bytecode: invalid variable register"
 	.endif
-- 
2.43.0