Add devcontainer setup for building

.devcontainer/devcontainer.json

@@ -0,0 +1,18 @@
+{
+	"name": "ZX Spectrum dev tools",
+	"image": "boarstone.mcphail.uk/mcphail/speccydev",
+	"remoteUser": "ubuntu",
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"maziac.dezog",
+				"maziac.asm-code-lens",
+				"maziac.z80-instruction-set",
+				"maziac.hex-hover-converter",
+				"maziac.sna-fileviewer",
+				"maziac.nex-fileviewer",
+				"ms-vscode.makefile-tools"
+			]
+		}
+	}
+}

xylo.asm

@@ -1,7 +1,7 @@
 org 51000
 
 counter EQU inc_counter + 1
-attrs EQU &5800
+attrs EQU #5800
 xylo EQU attrs + 40
 
 zero_counter:
@@ -11,8 +11,8 @@ set_counter:
 	ld (counter), a
 
 read_keyboard:
-	ld a, &f7
-	in a, (&fe)
+	ld a, #f7
+	in a, (#fe)
 	rra
 	jr nc, key_1
 	rra
@@ -22,56 +22,33 @@ read_keyboard:
 	rra
 	jr nc, key_4
 	rra
-	jr nc, key_5
-	jr read_keyboard
-
-key_1:
-	ld c, 0
-	call highlight_key
-	ld a, (counter)
-	call play
-	ld c, 0
-	call highlight_key
-	jr inc_counter
-
-key_2:
-	ld c, 3
-	call highlight_key
-	ld a, (counter)
-	inc a
-	call play
-	ld c, 3
-	call highlight_key
-	jr inc_counter
-
-key_3:
-	ld c, 6
-	call highlight_key
-	ld a, (counter)
-	inc a
-	inc a
-	call play
-	ld c, 6
-	call highlight_key
-	jr inc_counter
-
-key_4:
-	ld c, 9
-	call highlight_key
-	ld a, (counter)
-	add a, 3
-	call play
-	ld c, 9
-	call highlight_key
-	jr inc_counter
+	jr c, read_keyboard
 
 key_5:
-	ld c, 12
+	ld de, #040C
+	jr invoke
+
+key_2:
+	ld de, #0103
+	jr invoke
+
+key_3:
+	ld de, #0206
+	jr invoke
+
+key_4:
+	ld de, #0309
+	jr invoke
+
+key_1:
+	ld de, #0000
+invoke:
+	push de
 	call highlight_key
 	ld a, (counter)
-	add a, 4
+	add a, d
 	call play
-	ld c, 12
+	pop de
 	call highlight_key
 
 inc_counter:
@@ -79,26 +56,26 @@ inc_counter:
 	add a, 5
 	cp 25
 	jr nz, set_counter
-	jp zero_counter
+	jr zero_counter
 
 highlight_key:
 	ld hl, xylo
-	ld b, 0
-	add hl, bc
-	ld d, 15
-highlight_row:
-	ld e, 3
-highlight_block:
+	push de
+	ld d, 0
+	add hl, de
+	ld e, 30
 	ld a, (hl)
 	xor %01000000
+	ld b, 15
+highlight_block:
 	ld (hl), a
 	inc hl
-	dec e
-	jr nz, highlight_block
-	ld c, 29
-	add hl, bc
-	dec d
-	jr nz, highlight_row
+	ld (hl), a
+	inc hl
+	ld (hl), a
+	add hl, de
+	djnz highlight_block
+	pop de
 	ret
 
 INCLUDE "sample.asm"