emul/hw/sms: add A/B ports and a Genesis pad

This makes the emulator suitable to run the base SMS recipe.

emul/emul.h

@@ -1,3 +1,4 @@
+#pragma once
 #include <stdint.h>
 #include <stdbool.h>
 #include "libz80/z80.h"
@@ -19,6 +20,12 @@ typedef struct {
     IOWR iowr[0x100];
 } Machine;
 
+typedef enum {
+    TRI_HIGH,
+    TRI_LOW,
+    TRI_HIGHZ
+} Tristate;
+
 Machine* emul_init();
 bool emul_step();
 bool emul_steps(unsigned int steps);

emul/hw/sms/Makefile

@@ -1,5 +1,5 @@
 EXTOBJS = ../../emul.o ../../libz80/libz80.o
-OBJS = sms.o vdp.o
+OBJS = sms.o vdp.o port.o pad.o
 TARGET = sms
 CFLAGS += `pkg-config --cflags xcb`
 LDFLAGS += `pkg-config --libs xcb`

emul/hw/sms/README.md

@@ -0,0 +1,25 @@
+# Sega Master System emulator
+
+This emulates a Sega Master system with a monochrome screen and a Genesis pad
+hooked to port A.
+
+## Build
+
+You need `xcb` and `pkg-config` to build this. If you have them, run `make`.
+You'll get a `sms` executable.
+
+## Usage
+
+Launch the emulator with `./sms /path/to/rom` (you can use the binary from the
+`sms` recipe.
+
+This will show a window with the screen's content on it. The mappings to the
+pad are:
+
+* Arrows
+* Z --> A
+* X --> B
+* C --> C
+* S --> Start
+
+Press ESC to quit.

emul/hw/sms/pad.c

@@ -0,0 +1,30 @@
+#include "pad.h"
+
+void pad_init(Pad *pad, Tristate *TH)
+{
+    pad->pressed = 0xff;
+    pad->TH = TH;
+}
+
+void pad_setbtn(Pad *pad, PAD_BTN btn, bool pressed)
+{
+    if (pressed) {
+        pad->pressed &= ~(1 << btn);
+    } else {
+        pad->pressed |= (1 << btn);
+    }
+}
+
+uint8_t pad_rd(Pad *pad)
+{
+    uint8_t res;
+    if (*pad->TH == TRI_LOW) { // TH selected
+        // A and START shifted in from bits 7:6 into 5:4
+        res = (pad->pressed & 0xf) | ((pad->pressed & 0xc0) >> 2);
+    } else {
+        res = pad->pressed & 0x3f;
+    }
+    // Bits 7:6 are always high
+    res |= 0b11000000;
+    return res;
+}

emul/hw/sms/pad.h

@@ -0,0 +1,23 @@
+#include <stdint.h>
+#include <stdbool.h>
+#include "port.h"
+
+typedef enum {
+    PAD_BTN_UP = 0,
+    PAD_BTN_DOWN = 1,
+    PAD_BTN_LEFT = 2,
+    PAD_BTN_RIGHT = 3,
+    PAD_BTN_B = 4,
+    PAD_BTN_C = 5,
+    PAD_BTN_A = 6,
+    PAD_BTN_START = 7
+} PAD_BTN;
+
+typedef struct {
+    uint8_t pressed;
+    Tristate *TH;
+} Pad;
+
+void pad_init(Pad *pad, Tristate *TH);
+void pad_setbtn(Pad *pad, PAD_BTN btn, bool pressed);
+uint8_t pad_rd(Pad *pad);

emul/hw/sms/port.c

@@ -0,0 +1,70 @@
+#include "port.h"
+
+void ports_init(Ports *ports)
+{
+    ports->ctl = 0xff;
+    ports->TRA = TRI_HIGHZ;
+    ports->THA = TRI_HIGHZ;
+    ports->TRB = TRI_HIGHZ;
+    ports->THB = TRI_HIGHZ;
+}
+
+uint8_t ports_ctl_rd(Ports *ports)
+{
+    return ports->ctl;
+}
+
+void ports_ctl_wr(Ports *ports, uint8_t val)
+{
+    ports->ctl = val;
+    ports->TRA = TRI_HIGHZ;
+    ports->THA = TRI_HIGHZ;
+    ports->TRB = TRI_HIGHZ;
+    ports->THB = TRI_HIGHZ;
+    if ((val & 0x01) == 0) {
+        ports->TRA = ((val & 0x10) == 0) ? TRI_LOW : TRI_HIGH;
+    }
+    if ((val & 0x02) == 0) {
+        ports->THA = ((val & 0x20) == 0) ? TRI_LOW : TRI_HIGH;
+    }
+    if ((val & 0x04) == 0) {
+        ports->TRB = ((val & 0x40) == 0) ? TRI_LOW : TRI_HIGH;
+    }
+    if ((val & 0x08) == 0) {
+        ports->THB = ((val & 0x80) == 0) ? TRI_LOW : TRI_HIGH;
+    }
+}
+
+uint8_t ports_A_rd(Ports *ports)
+{
+    // Bits 7:6 are port B's Down/Up
+    // Bits 5:0 are port A's TR/TL/R/L/D/U
+    uint8_t res = 0xff;
+    if (ports->portA_rd != NULL) {
+        res &= ports->portA_rd() | 0b11000000;
+    }
+    if (ports->portB_rd != NULL) {
+        res &= (ports->portB_rd() << 6) | 0b00111111;
+    }
+    return res;
+
+}
+
+uint8_t ports_B_rd(Ports *ports)
+{
+    // Bit 7: Port B's TH
+    // Bit 6: Port A's TH
+    // Bit 5: unused
+    // Bit 4: unused (reset button)
+    // Bits 3:0 are port B's TR/TL/R/L
+    uint8_t res = 0xff;
+    if (ports->portA_rd != NULL) {
+        res &= ports->portA_rd() | 0b10111111;
+    }
+    if (ports->portB_rd != NULL) {
+        uint8_t portb = ports->portB_rd();
+        res &= (portb << 1) | 0b01111111; // TH
+        res &= (portb >> 2) | 0b11110000; // TR/TL/R/L
+    }
+    return res;
+}

emul/hw/sms/port.h

@@ -0,0 +1,21 @@
+#pragma once
+#include "../../emul.h"
+
+// Each port is a bitmask of each pin's status. 1 means high.
+// From Bit 0 to 6: up, down, left, right, TL, TR, TH
+
+typedef struct {
+    uint8_t ctl;
+    Tristate TRA;
+    Tristate THA;
+    Tristate TRB;
+    Tristate THB;
+    IORD portA_rd;
+    IORD portB_rd;
+} Ports;
+
+void ports_init(Ports *ports);
+uint8_t ports_ctl_rd(Ports *ports);
+void ports_ctl_wr(Ports *ports, uint8_t val);
+uint8_t ports_A_rd(Ports *ports);
+uint8_t ports_B_rd(Ports *ports);

emul/hw/sms/sms.c

@@ -6,10 +6,15 @@
 
 #include "../../emul.h"
 #include "vdp.h"
+#include "port.h"
+#include "pad.h"
 
 #define RAMSTART 0xc000
 #define VDP_CMD_PORT 0xbf
 #define VDP_DATA_PORT 0xbe
+#define PORTS_CTL_PORT 0x3f
+#define PORTS_IO1_PORT 0xdc
+#define PORTS_IO2_PORT 0xdd
 #define MAX_ROMSIZE 0x8000
 
 static xcb_connection_t    *conn;
@@ -26,6 +31,8 @@ static xcb_rectangle_t rectangles[VDP_SCREENW*VDP_SCREENH];
 static Machine *m;
 static VDP vdp;
 static bool vdp_changed;
+static Ports ports;
+static Pad pad;
 
 static uint8_t iord_vdp_cmd()
 {
@@ -37,6 +44,21 @@ static uint8_t iord_vdp_data()
     return vdp_data_rd(&vdp);
 }
 
+static uint8_t iord_ports_io1()
+{
+    return ports_A_rd(&ports);
+}
+
+static uint8_t iord_ports_io2()
+{
+    return ports_B_rd(&ports);
+}
+
+static uint8_t iord_pad()
+{
+    return pad_rd(&pad);
+}
+
 static void iowr_vdp_cmd(uint8_t val)
 {
     vdp_cmd_wr(&vdp, val);
@@ -48,6 +70,11 @@ static void iowr_vdp_data(uint8_t val)
     vdp_data_wr(&vdp, val);
 }
 
+static void iowr_ports_ctl(uint8_t val)
+{
+    ports_ctl_wr(&ports, val);
+}
+
 void create_window()
 {
     uint32_t mask;
@@ -150,7 +177,34 @@ void event_loop()
         case XCB_KEY_RELEASE:
         case XCB_KEY_PRESS: {
             xcb_key_press_event_t *ev = (xcb_key_press_event_t *)e;
-            if (ev->detail == 0x09) return;
+            bool ispressed = e->response_type == XCB_KEY_PRESS;
+            switch (ev->detail) {
+                case 0x09: return; // ESC
+                case 0x27:  // S
+                    pad_setbtn(&pad, PAD_BTN_START, ispressed);
+                    break;
+                case 0x34:  // Z
+                    pad_setbtn(&pad, PAD_BTN_A, ispressed);
+                    break;
+                case 0x35:  // X
+                    pad_setbtn(&pad, PAD_BTN_B, ispressed);
+                    break;
+                case 0x36:  // C
+                    pad_setbtn(&pad, PAD_BTN_C, ispressed);
+                    break;
+                case 0x62:
+                    pad_setbtn(&pad, PAD_BTN_UP, ispressed);
+                    break;
+                case 0x64:
+                    pad_setbtn(&pad, PAD_BTN_LEFT, ispressed);
+                    break;
+                case 0x66:
+                    pad_setbtn(&pad, PAD_BTN_RIGHT, ispressed);
+                    break;
+                case 0x68:
+                    pad_setbtn(&pad, PAD_BTN_DOWN, ispressed);
+                    break;
+            }
             break;
         }
         case XCB_EXPOSE: {
@@ -190,10 +244,16 @@ int main(int argc, char *argv[])
     }
     vdp_init(&vdp);
     vdp_changed = false;
+    ports_init(&ports);
+    ports.portA_rd = iord_pad;
+    pad_init(&pad, &ports.THA);
     m->iord[VDP_CMD_PORT] = iord_vdp_cmd;
     m->iord[VDP_DATA_PORT] = iord_vdp_data;
+    m->iord[PORTS_IO1_PORT] = iord_ports_io1;
+    m->iord[PORTS_IO2_PORT] = iord_ports_io2;
     m->iowr[VDP_CMD_PORT] = iowr_vdp_cmd;
     m->iowr[VDP_DATA_PORT] = iowr_vdp_data;
+    m->iowr[PORTS_CTL_PORT] = iowr_ports_ctl;
     conn = xcb_connect(NULL, NULL);
     screen = xcb_setup_roots_iterator(xcb_get_setup(conn)).data;
     create_window();