Scroll screen; remove volatile.

main.c

@@ -1,3 +1,5 @@
+#include <string.h>
+
 #include "exporter.h"
 #include "platform.h"
 #include "runtime.h"
@@ -47,40 +49,6 @@ void (*g_compiled_function)() = (void (*)()) g_compiled;
 // - Nul.
 uint8_t g_program[1024];
 
-
-/**
- * Copy a memory buffer. Source and destination may overlap.
- */
-static void memmove(uint8_t *dest, uint8_t *src, uint16_t count) {
-    // See if we overlap.
-    if (dest > src && dest < src + count) {
-        // Overlapping with src before dest, we have to copy backward.
-        dest += count;
-        src += count;
-        while (count-- > 0) {
-            *--dest = *--src;
-        }
-    } else {
-        // No overlap, or dest before src, which is fine.
-        while (count-- > 0) {
-            *dest++ = *src++;
-        }
-    }
-}
-
-/**
- * Get the length of a nul-terminated string.
- */
-static int16_t strlen(uint8_t *s) {
-    uint8_t *original = s;
-
-    while (*s != '\0') {
-        s += 1;
-    }
-
-    return s - original;
-}
-
 /**
  * Print the tokenized string, with tokens displayed as their full text.
  * Prints a newline at the end.
@@ -190,20 +158,6 @@ static void add_return() {
     g_compiled[g_compiled_length++] = I_RTS;
 }
 
-/**
- * Advance s over whitespace, which is just a space, returning
- * the new pointer.
- */
-/* Unused.
-static uint8_t *skip_whitespace(uint8_t *s) {
-    while (*s == ' ') {
-        s += 1;
-    }
-
-    return s;
-}
-*/
-
 /**
  * Parse an unsigned integer, returning the value and moving the pointer
  * past the end of the number. The pointer must already be at the beginning
@@ -421,7 +375,7 @@ static void process_input_buffer() {
         // Dump compiled buffer to the terminal.
         {
             int i;
-            volatile uint8_t *debug_port = (uint8_t *) 0xBFFE;
+            uint8_t *debug_port = (uint8_t *) 0xBFFE;
             debug_port[0] = g_compiled_length;
             for (i = 0; i < g_compiled_length; i++) {
                 debug_port[1] = g_compiled[i];
@@ -522,7 +476,7 @@ int16_t main(void)
     if (1) {
         int16_t i;
         for (i = 0; i < 256; i++) {
-            volatile uint8_t *loc;
+            uint8_t *loc;
             // Fails with: unhandled instruction B2
             move_cursor(i % 16, i >> 4);
             // Works.
@@ -540,6 +494,9 @@ int16_t main(void)
 
     // Prompt.
     print("\n\n]");
+    // TODO crashes 6502. Delete:
+    // asm("ldy #1");
+    // asm("sta $FFFF,y");
 
     // Keyboard input.
     blink = 0;
@@ -572,7 +529,7 @@ int16_t main(void)
                     }
                 } else if (key == 13) {
                     // Return.
-                    move_cursor(0, g_cursor_y + 1);
+                    print_char('\n');
 
                     process_input_buffer();
 
@@ -580,7 +537,7 @@ int16_t main(void)
                     g_input_buffer_length = 0;
                 } else {
                     if (g_input_buffer_length < sizeof(g_input_buffer) - 1) {
-                        volatile uint8_t *loc = cursor_pos();
+                        uint8_t *loc = cursor_pos();
                         *loc = key | 0x80;
                         move_cursor(g_cursor_x + 1, g_cursor_y);
 

platform.c

@@ -1,7 +1,7 @@
 #include "platform.h"
 
-#define KBD_STATUS_OR_KEY ((volatile unsigned char *)0xC000)
-#define KBD_CLEAR_CURRENT_KEY ((volatile unsigned char *)0xC010)
+#define KBD_STATUS_OR_KEY ((unsigned char *)0xC000)
+#define KBD_CLEAR_CURRENT_KEY ((unsigned char *)0xC010)
 
 #define KEY_READY_MASK 0x80
 #define KEY_VALUE_MASK 0x7F

platform.h

@@ -1,8 +1,8 @@
 #ifndef __PLATFORM_H__
 #define __PLATFORM_H__
 
-#define TEXT_PAGE1_BASE ((volatile unsigned char *)0x400)
-#define TEXT_PAGE2_BASE ((volatile unsigned char *)0x800)
+#define TEXT_PAGE1_BASE ((unsigned char *)0x400)
+#define TEXT_PAGE2_BASE ((unsigned char *)0x800)
 
 // Standard types.
 typedef signed char int8_t;

runtime.c

@@ -1,7 +1,9 @@
 
+#include <string.h>
 #include "runtime.h"
 
 #define CURSOR_GLYPH 127
+#define SCREEN_HEIGHT 24
 #define SCREEN_WIDTH 40
 #define SCREEN_STRIDE (3*SCREEN_WIDTH + 8)
 
@@ -13,14 +15,21 @@ uint16_t g_showing_cursor = 0;
 // Character at the cursor location.
 uint8_t g_cursor_ch = 0;
 
+/**
+ * Return the memory location of the zero-based (x,y) position on the screen.
+ */
+static uint8_t *screen_pos(uint16_t x, uint16_t y) {
+    int16_t block = y >> 3;
+    int16_t line = y & 0x07;
+
+    return TEXT_PAGE1_BASE + line*SCREEN_STRIDE + block*SCREEN_WIDTH + x;
+}
+
 /**
  * Return the memory location of the cursor.
  */
-volatile uint8_t *cursor_pos(void) {
-    int16_t block = g_cursor_y >> 3;
-    int16_t line = g_cursor_y & 0x07;
-
-    return TEXT_PAGE1_BASE + line*SCREEN_STRIDE + block*SCREEN_WIDTH + g_cursor_x;
+uint8_t *cursor_pos(void) {
+    return screen_pos(g_cursor_x, g_cursor_y);
 }
 
 /**
@@ -28,7 +37,7 @@ volatile uint8_t *cursor_pos(void) {
  */
 void show_cursor(void) {
     if (!g_showing_cursor) {
-        volatile uint8_t *pos = cursor_pos();
+        uint8_t *pos = cursor_pos();
         g_cursor_ch = *pos;
         *pos = CURSOR_GLYPH | 0x80;
         g_showing_cursor = 1;
@@ -40,7 +49,7 @@ void show_cursor(void) {
  */
 void hide_cursor(void) {
     if (g_showing_cursor) {
-        volatile uint8_t *pos = cursor_pos();
+        uint8_t *pos = cursor_pos();
         *pos = g_cursor_ch;
         g_showing_cursor = 0;
     }
@@ -60,27 +69,45 @@ void move_cursor(int16_t x, int16_t y) {
  * Clear the screen with non-reversed spaces.
  */
 void home(void) {
-    volatile uint8_t *p = TEXT_PAGE1_BASE;
-    uint8_t ch = ' ' | 0x80;
-    int16_t i;
+    memset(TEXT_PAGE1_BASE, ' ' | 0x80, SCREEN_STRIDE*8);
+    move_cursor(0, 0);
+}
 
-    // TODO: Could write these as words, not chars.
-    for (i = SCREEN_STRIDE*8; i >= 0; i--) {
-        *p++ = ch;
+/**
+ * Screen the screen up one line, blanking out the bottom
+ * row. Does not affect the cursor.
+ */
+static void scroll_up(void) {
+    int i;
+    uint8_t *previous_line = 0;
+
+    for (i = 0; i < SCREEN_HEIGHT; i++) {
+        uint8_t *this_line = screen_pos(0, i);
+        if (i > 0) {
+            memmove(previous_line, this_line, SCREEN_WIDTH);
+        }
+        previous_line = this_line;
     }
 
-    move_cursor(0, 0);
+    // This is provided by cc65:
+    memset(previous_line, ' ' | 0x80, SCREEN_WIDTH);
 }
 
 /**
  * Prints the character and advances the cursor. Handles newlines.
  */
 void print_char(uint8_t c) {
-    volatile uint8_t *loc = cursor_pos();
+    uint8_t *loc = cursor_pos();
 
     if (c == '\n') {
-        // TODO: Scroll.
-        move_cursor(0, g_cursor_y + 1);
+        if (g_cursor_y == SCREEN_HEIGHT - 1) {
+            // Scroll.
+            hide_cursor();
+            scroll_up();
+            move_cursor(0, g_cursor_y);
+        } else {
+            move_cursor(0, g_cursor_y + 1);
+        }
     } else {
         // Print character.
         *loc = c | 0x80;

runtime.h

@@ -8,7 +8,7 @@ extern uint16_t g_cursor_y;
 extern uint16_t g_showing_cursor;
 extern uint8_t g_cursor_ch;
 
-volatile uint8_t *cursor_pos(void);
+uint8_t *cursor_pos(void);
 void show_cursor(void);
 void hide_cursor(void);
 void move_cursor(int16_t x, int16_t y);