Polish VRAM access to TTY TX emulation

It assumes Apple BASIC's manner of controlling screen.
Apple BASIC may be able to work exactly like running through
a virtual terminal device.

Makefile

@@ -5,7 +5,8 @@ LD	= arm-none-eabi-ld
 OBJCOPY	= arm-none-eabi-objcopy
 LDSCRIPT= lpc1114.ld
 LPC21ISP= lpc21isp
-SERIAL	= /dev/ttyUSB0
+#SERIAL	= /dev/ttyUSB0
+SERIAL	= /dev/ttyUSB1
 #SERIAL	= /dev/ttyACM0
 SPEED	= 115200
 #SPEED	= 9600

apple2.S

@@ -164,7 +164,8 @@ cpu6502_load:
   orrs r0, r0, r1
   ldr  r1, =#kbddata
   strb r0, [r1]
-  b    3b
+  // Drop old input data?
+  // b    3b
 2:
   ldr  r2, =#kbddata
   ldrb r0, [r2]
@@ -360,20 +361,18 @@ a2_tty:
   strb r0, [r3]
 1:
   cmp  r0, #4
-  bne 2f
+  bne 3f
   // scrmode 4 (normal)
-  //cmp  r1, #0xff
-  //bne  1f
-  //pop  {pc}
-1:
-  //cmp  r1, #0x7f
-  //bne  1f
-  //pop  {pc}
 1:
   movs r3, #0x04
   lsls r3, r3, #8
   subs r3, r2, r3
   movs r2, r3
+  cmp  r2, #0x27
+  bne  1f
+  cmp  r1, #0xff
+  beq  2f
+1:
   movs r0, #0x7f
   ands r2, r2, r0
   lsrs r3, r3, #7
@@ -403,8 +402,42 @@ a2_tty:
 1:
   mov  r0, r1
   bl   a2_putc
+  pop  {pc}
+2:
+  ldr  r0, =#scrmode
+  movs r1, #5
+  strb r1, [r0]
+3:
+  cmp  r0, #5
+  bne  2f
+  // scrmode 5 (Waitinf for scroll finished)
+  movs r3, #0x07
+  lsls r3, r3, #8
+  movs r0, #0xf7
+  adds r3, r3, r0
+  cmp  r2, r3
+  beq  1f
+  pop  {pc}
+1:
+  ldr  r0, =#scrline
+  ldrb r0, [r0]
+  movs r1, #24
+  subs r1, r0
+1:
+  movs r0, #0x0a
+  push {r1}
+  bl   uart_putc
+  pop  {r1}
+  subs r1, r1, #1
+  bne  1b
+
+  ldr  r1, =#scrmode
+  movs r0, #4
+  strb r0, [r1]
+  ldr  r1, =#scrline
+  movs r0, #23
+  strb r0, [r1]
 2:
-  // TODO: scroll
   pop  {pc}
 
   .bss

test.c

@@ -45,7 +45,7 @@ uint8_t cpu6502_load(uint16_t addr) {
   if (0x0400 <= addr && addr <= 0x7ff) {
     // Fake text VRAM.
     result = mem[addr];
-    result = '@';
+    result = 0xff;
   } else if ((0x0300 <= addr && addr <= 0x03ff) ||
              (0x0900 <= addr && addr <= 0x0fff)) {
     // Fake memory impl to make it run on low memory chip.
@@ -108,7 +108,7 @@ void cpu6502_store(uint16_t addr, uint8_t data) {
     //       clear x, y
     // 2) Show "APPLE ][" from back to forth.
     // 3) Count down from G to A at x = 40, y = 23
-    // 4) Scroll happens on CR at line 22 or 23, left to right, up to down
+    // 4) Scroll happens on CR at line 22 or 23, right to left, up to down
     //   for (var y = 0; y < 23; ++y)
     //     for (var x = 39; x >= 0; --x)
     //       reset x, y
@@ -116,7 +116,7 @@ void cpu6502_store(uint16_t addr, uint8_t data) {
     //     clear x, 23
     //   prompt 0, 23
     //fprintf(stdout, "\e[%d;%dH%c", y + 7, x + 1, ascii[data & 0x3f]);
-    fprintf(stdout, "(%2d,%2d)%c($%02x)\n", x, y, ascii[data & 0x3f], data);
+    fprintf(stdout, "(%2d,%2d)@%04x%c($%02x)\n", x, y, addr, ascii[data & 0x3f], data);
     fflush(stdout);
   } else if ((0x0300 <= addr && addr <= 0x03ff) ||
              (0x0900 <= addr && addr <= 0x0fff)) {