Start implementation of display emulation.

Something like a character RAM for a start. When 65C02 writes into
this space, a callback will be executed that would allow redrawing
the emulated screen. Multiple backends can be supported this way.

src/Makefile

@@ -1,7 +1,7 @@
 CLI=rk65c02cli
 CLI_OBJS=rk65c02cli.o
 
-LIB_OBJS=rk65c02.o bus.o instruction.o emulation.o debug.o device_ram.o device_serial.o log.o
+LIB_OBJS=rk65c02.o bus.o instruction.o emulation.o debug.o device_ram.o device_fb.o device_serial.o log.o
 LIB_SO=librk65c02.so
 LIB_STATIC=librk65c02.a
 

src/device_fb.c

@@ -0,0 +1,87 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <string.h>
+
+#include "bus.h"
+#include "device.h"
+
+#define FB_AS_SIZE	0x1000
+
+#define CHAR_RAM_SIZE	(80*50)	/* 0xFA0 */
+#define CHAR_FONT_WIDTH	8
+#define CHAR_FONT_HEIGHT 8
+
+struct fb_state {
+	uint8_t *cram;
+
+	void (*fb_callback_screen_update)(uint8_t *);
+};
+
+uint8_t device_fb_read_1(void *, uint16_t);
+void device_fb_write_1(void *, uint16_t, uint8_t);
+
+uint8_t
+device_fb_read_1(void *vd, uint16_t offset)
+{
+	device_t *d;
+	struct fb_state *f;
+
+	d = (device_t *) vd;
+	f = d->aux;
+
+	return f->cram[offset];
+}
+
+void
+device_fb_write_1(void *vd, uint16_t offset, uint8_t val)
+{
+	device_t *d;
+
+	struct fb_state *f;
+
+	d = (device_t *) vd;
+	f = d->aux;
+
+	f->cram[offset] = val;
+
+	if (f->fb_callback_screen_update != NULL)
+		f->fb_callback_screen_update(f->cram);
+}
+
+device_t *
+device_fb_init()
+{
+	device_t *d;
+	struct fb_state *f;
+
+	d = (device_t *) malloc(sizeof(device_t));
+
+	assert(d != NULL);
+
+	d->name = "FB";
+	d->size = FB_AS_SIZE;
+
+	d->read_1 = device_fb_read_1;
+	d->write_1 = device_fb_write_1;
+
+	f = malloc(sizeof(struct fb_state));
+	d->aux = f;
+
+	f->cram = malloc(FB_AS_SIZE);
+	memset(d->aux, 0, FB_AS_SIZE);
+
+	return d;
+}
+
+void
+device_fb_finish(device_t *d)
+{
+	struct fb_state *f;
+
+	f = d->aux;
+
+	free(f->cram);
+	free(f);
+}
+

src/device_fb.h

@@ -0,0 +1,9 @@
+#ifndef _DEVICE_RAM_H_
+#define _DEVICE_RAM_H_
+
+#include "device.h"
+
+device_t * device_fb_init();
+void device_fb_finish(device_t *);
+
+#endif /* _DEVICE_RAM_H_ */