emul/z80: extract tms9918 unit from sms_vdp

I'm planning on supporting Text Mode soon, and SMS' VDP, when mode
4 is not active, behaves mostly like a regular TMS9918.

By having this behavior in a separate unit, we'll be able to use it
in other systems.

emul/z80/Makefile

@@ -1,7 +1,8 @@
 TARGETS = forth rc2014 sms ti84
 OBJS = emul.o z80.o
 RC2014_OBJS = $(OBJS) sio.o acia.o sdc.o rc2014_spi.o
-SMS_OBJS = $(OBJS) sms_vdp.o sms_ports.o sms_pad.o ps2_kbd.o sdc.o sms_spi.o
+SMS_OBJS = $(OBJS) tms9918.o sms_vdp.o sms_ports.o sms_pad.o ps2_kbd.o sdc.o \
+	sms_spi.o
 TI84_OBJS = $(OBJS) t6a04.o ti84_kbd.o 
 CDIR = ../../cvm
 STAGE = $(CDIR)/stage

emul/z80/sms.c

@@ -48,7 +48,7 @@ static SPI spi;
 
 static uint8_t iord_vdp_cmd()
 {
-    return vdp_cmd_rd(&vdp);
+    return tms_cmd_rd(&vdp.tms);
 }
 
 static uint8_t iord_vdp_data()

emul/z80/sms_vdp.c

@@ -3,55 +3,47 @@
 
 void vdp_init(VDP *vdp)
 {
-    memset(vdp->vram, 0, VDP_VRAM_SIZE);
-    memset(vdp->regs, 0, 0x10);
-    vdp->has_cmdlsb = false;
-    vdp->curaddr = 0;
-}
-
-uint8_t vdp_cmd_rd(VDP *vdp)
-{
-    return 0;
+    tms_init(&vdp->tms);
+    memset(vdp->cram, 0, VDP_CRAM_SIZE);
 }
 
 void vdp_cmd_wr(VDP *vdp, uint8_t val)
 {
-    if (!vdp->has_cmdlsb) {
-        vdp->cmdlsb = val;
-        vdp->has_cmdlsb = true;
-        return;
-    }
-    vdp->has_cmdlsb = false;
-    if ((val & 0xc0) == 0x80) {
-        // set register
-        vdp->regs[val&0xf] = vdp->cmdlsb;
-    } else if ((val & 0xc0) == 0xc0) {
-        // palette RAM
-        vdp->curaddr = 0x4000 + (vdp->cmdlsb&0x1f);
+    if (!vdp->tms.has_cmdlsb) {
+        tms_cmd_wr(&vdp->tms, val);
     } else {
-        // VRAM
-        vdp->curaddr = ((val&0x3f) << 8) + vdp->cmdlsb;
+        if ((val & 0xc0) == 0xc0) {
+            // palette RAM
+            // curaddr > VRAM == addr in CRAM
+            vdp->tms.curaddr = TMS_VRAM_SIZE + (vdp->tms.cmdlsb&0x1f);
+        } else {
+            tms_cmd_wr(&vdp->tms, val);
+        }
     }
 }
 
 uint8_t vdp_data_rd(VDP *vdp)
 {
-    uint8_t res = vdp->vram[vdp->curaddr];
-    if (vdp->curaddr < VDP_VRAM_SIZE) {
-        vdp->curaddr++;
+    TMS9918 *tms = &vdp->tms;
+    if (tms->curaddr < TMS_VRAM_SIZE) {
+        return tms_data_rd(&vdp->tms);
+    } else if (tms->curaddr - TMS_VRAM_SIZE < VDP_CRAM_SIZE) {
+        return vdp->cram[tms->curaddr++-TMS_VRAM_SIZE];
+    } else {
+        return 0;
     }
-    return res;
 }
 
 void vdp_data_wr(VDP *vdp, uint8_t val)
 {
-    vdp->vram[vdp->curaddr] = val;
-    if (vdp->curaddr < VDP_VRAM_SIZE) {
-        vdp->curaddr++;
+    TMS9918 *tms = &vdp->tms;
+    if (tms->curaddr < TMS_VRAM_SIZE) {
+        tms_data_wr(&vdp->tms, val);
+    } else if (tms->curaddr - TMS_VRAM_SIZE < VDP_CRAM_SIZE) {
+        vdp->cram[tms->curaddr++-TMS_VRAM_SIZE] = val;
     }
 }
 
-// Returns a 8-bit RGB value (0b00bbggrr)
 uint8_t vdp_pixel(VDP *vdp, uint16_t x, uint16_t y)
 {
     if (x >= VDP_SCREENW) {
@@ -60,10 +52,11 @@ uint8_t vdp_pixel(VDP *vdp, uint16_t x, uint16_t y)
     if (y >= VDP_SCREENH) {
         return 0;
     }
+    TMS9918 *tms = &vdp->tms;
     // name table offset
-    uint16_t offset = (vdp->regs[2] & 0xe) << 10;
+    uint16_t offset = (tms->regs[2] & 0xe) << 10;
     offset += ((y/8) << 6) + ((x/8) << 1);
-    uint16_t tableval = vdp->vram[offset] + (vdp->vram[offset+1] << 8);
+    uint16_t tableval = tms->vram[offset] + (tms->vram[offset+1] << 8);
     uint16_t tilenum = tableval & 0x1ff;
     // is palette select bit on? if yes, use sprite palette instead
     uint8_t palettemod = tableval & 0x800 ? 0x10 : 0;
@@ -74,10 +67,10 @@ uint8_t vdp_pixel(VDP *vdp, uint16_t x, uint16_t y)
     uint8_t bitnum = 7 - (x%8);
     // Now, let's compose the result by pushing the right bit of our 4 bytes
     // into our result.
-    uint8_t palette_id = ((vdp->vram[offset] >> bitnum) & 1) + \
-           (((vdp->vram[offset+1] >> bitnum) & 1) << 1) + \
-           (((vdp->vram[offset+2] >> bitnum) & 1) << 2) + \
-           (((vdp->vram[offset+3] >> bitnum) & 1) << 3);
-    uint8_t rgb = vdp->vram[0x4000+palettemod+palette_id];
+    uint8_t palette_id = ((tms->vram[offset] >> bitnum) & 1) + \
+           (((tms->vram[offset+1] >> bitnum) & 1) << 1) + \
+           (((tms->vram[offset+2] >> bitnum) & 1) << 2) + \
+           (((tms->vram[offset+3] >> bitnum) & 1) << 3);
+    uint8_t rgb = vdp->cram[palettemod+palette_id];
     return rgb;
 }

emul/z80/sms_vdp.h

@@ -1,26 +1,16 @@
-#include <stdint.h>
-#include <stdbool.h>
+#include "tms9918.h"
 
-#define VDP_VRAM_SIZE 0x4020
+#define VDP_CRAM_SIZE 0x20
 #define VDP_SCREENW (32*8)
 #define VDP_SCREENH (24*8)
-// Offset of the name table
-#define VDP_NTABLE_OFFSET 0x3800
-
 
 typedef struct {
-    // the last 0x20 is palette RAM
-    uint8_t vram[VDP_VRAM_SIZE];
-    uint8_t regs[0x10];
-    uint8_t cmdlsb;
-    bool has_cmdlsb;
-    uint16_t curaddr;
+    TMS9918 tms;
+    uint8_t cram[VDP_CRAM_SIZE];
 } VDP;
 
 void vdp_init(VDP *vdp);
-uint8_t vdp_cmd_rd(VDP *vdp);
 void vdp_cmd_wr(VDP *vdp, uint8_t val);
 uint8_t vdp_data_rd(VDP *vdp);
 void vdp_data_wr(VDP *vdp, uint8_t val);
-// result is a RGB value
 uint8_t vdp_pixel(VDP *vdp, uint16_t x, uint16_t y);

emul/z80/tms9918.c

@@ -0,0 +1,54 @@
+#include <string.h>
+#include "tms9918.h"
+
+void tms_init(TMS9918 *tms)
+{
+    memset(tms->vram, 0, TMS_VRAM_SIZE);
+    memset(tms->regs, 0, 0x10);
+    tms->has_cmdlsb = false;
+    tms->curaddr = 0;
+}
+
+uint8_t tms_cmd_rd(TMS9918 *tms)
+{
+    return 0;
+}
+
+void tms_cmd_wr(TMS9918 *tms, uint8_t val)
+{
+    if (!tms->has_cmdlsb) {
+        tms->cmdlsb = val;
+        tms->has_cmdlsb = true;
+        return;
+    }
+    tms->has_cmdlsb = false;
+    if ((val & 0xc0) == 0x80) {
+        // set register
+        tms->regs[val&0xf] = tms->cmdlsb;
+    } else {
+        // VRAM
+        tms->curaddr = ((val&0x3f) << 8) + tms->cmdlsb;
+    }
+}
+
+uint8_t tms_data_rd(TMS9918 *tms)
+{
+    if (tms->curaddr < TMS_VRAM_SIZE) {
+        return tms->vram[tms->curaddr++];
+    } else {
+        return 0;
+    }
+}
+
+void tms_data_wr(TMS9918 *tms, uint8_t val)
+{
+    if (tms->curaddr < TMS_VRAM_SIZE) {
+        tms->vram[tms->curaddr++] = val;
+    }
+}
+
+// Returns a 8-bit RGB value (0b00bbggrr)
+uint8_t tms_pixel(TMS9918 *tms, uint16_t x, uint16_t y)
+{
+    return 0; // no TMS9918 mode implemented yet
+}

emul/z80/tms9918.h

@@ -0,0 +1,24 @@
+#pragma once
+#include <stdint.h>
+#include <stdbool.h>
+
+#define TMS_VRAM_SIZE 0x4000
+// Offset of the name table
+#define TMS_NTABLE_OFFSET 0x3800
+
+
+typedef struct {
+    uint8_t vram[TMS_VRAM_SIZE];
+    uint8_t regs[0x10];
+    uint8_t cmdlsb;
+    bool has_cmdlsb;
+    uint16_t curaddr;
+} TMS9918;
+
+void tms_init(TMS9918 *tms);
+uint8_t tms_cmd_rd(TMS9918 *tms);
+void tms_cmd_wr(TMS9918 *tms, uint8_t val);
+uint8_t tms_data_rd(TMS9918 *tms);
+void tms_data_wr(TMS9918 *tms, uint8_t val);
+// result is a RGB value
+uint8_t tms_pixel(TMS9918 *tms, uint16_t x, uint16_t y);