emul/z80/sms: add SPI exchange through controller port

Theoretically, it works. I can access an emulated SD card on it.

Will it work on real hardware?

I've also made SMS emulation faster. It was unbearably slow for SDC
access.

emul/z80/Makefile

@@ -1,7 +1,7 @@
 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_OBJS = $(OBJS) 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

@@ -11,6 +11,7 @@
 #include "sms_vdp.h"
 #include "sms_ports.h"
 #include "sms_pad.h"
+#include "sms_spi.h"
 #include "ps2_kbd.h"
 #include "sdc.h"
 
@@ -43,6 +44,7 @@ static Pad pad;
 static Kbd kbd;
 static bool use_kbd = false;
 static SDC sdc;
+static SPI spi;
 
 static uint8_t iord_vdp_cmd()
 {
@@ -90,28 +92,12 @@ static void iowr_ports_ctl(uint8_t val)
     ports_ctl_wr(&ports, val);
 }
 
-// TODO: re-add as controller-based SPI
-/* static uint8_t iord_sdc_spi()
+static byte iord_spi()
 {
-    return sdc_spi_rd(&sdc);
+    return spi_rd(&spi);
 }
 
-static void iowr_sdc_spi(uint8_t val)
-{
-    sdc_spi_wr(&sdc, val);
-}
-
-// in emulation, exchanges are always instantaneous, so we
-// always report as ready.
-static uint8_t iord_sdc_ctl()
-{
-    return 0;
-}
-
-static void iowr_sdc_ctl(uint8_t val)
-{
-    sdc_ctl_wr(&sdc, val);
-}*/
+static byte spix_sdc(byte val) { return sdc_spix(&sdc, val); }
 
 void create_window()
 {
@@ -246,15 +232,25 @@ static bool _handle_keypress(xcb_generic_event_t *e)
 void event_loop()
 {
     while (1) {
-        if (!emul_step()) {
-            fprintf(stderr, "CPU halted, quitting\n");
-            usleep(1000 * 1000);
-            break;
+        for (int i=0; i<100; i++) {
+            if (!emul_step()) {
+                fprintf(stderr, "CPU halted, quitting\n");
+                usleep(1000 * 1000);
+                break;
+            }
+            spi_pulse(&spi);
         }
         if (vdp_changed) {
             // To avoid overdrawing, we'll let the CPU run a bit to finish its
             // drawing operation.
-            emul_steps(10000);
+            for (int i=0; i<10000; i++) {
+                if (!emul_step()) {
+                    fprintf(stderr, "CPU halted, quitting\n");
+                    usleep(1000 * 1000);
+                    break;
+                }
+                spi_pulse(&spi);
+            }
             draw_pixels();
         }
         // A low tech way of checking when the window was closed. The proper way
@@ -293,6 +289,12 @@ static void usage()
     fprintf(stderr, "Usage: ./sms [-k] [-c sdcard.img] /path/to/rom\n");
 }
 
+static byte spi_dbg(byte val)
+{
+    fprintf(stderr, "SPI XCH: %x\n", val);
+    return val+1;
+}
+
 int main(int argc, char *argv[])
 {
     if (argc < 2) {
@@ -305,6 +307,7 @@ int main(int argc, char *argv[])
     pad_init(&pad, &ports.THA);
     kbd_init(&kbd, &ports.THA);
     sdc_init(&sdc);
+    spi_init(&spi, &ports.THB, &ports.TRB, spix_sdc);
 
     int ch;
     while ((ch = getopt(argc, argv, "kc:")) != -1) {
@@ -348,6 +351,7 @@ int main(int argc, char *argv[])
     } else {
         ports.portA_rd = iord_pad;
     }
+    ports.portB_rd = iord_spi;
 
     m->iord[VDP_CMD_PORT] = iord_vdp_cmd;
     m->iord[VDP_DATA_PORT] = iord_vdp_data;
@@ -357,12 +361,6 @@ int main(int argc, char *argv[])
     m->iowr[VDP_CMD_PORT] = iowr_vdp_cmd;
     m->iowr[VDP_DATA_PORT] = iowr_vdp_data;
     m->iowr[PORTS_CTL_PORT] = iowr_ports_ctl;
-    /* TODO: re-add
-    m->iord[SDC_SPI] = iord_sdc_spi;
-    m->iowr[SDC_SPI] = iowr_sdc_spi;
-    m->iord[SDC_CTL] = iord_sdc_ctl;
-    m->iowr[SDC_CTL] = iowr_sdc_ctl;
-    */
 
     conn = xcb_connect(NULL, NULL);
     screen = xcb_setup_roots_iterator(xcb_get_setup(conn)).data;

emul/z80/sms_spi.c

@@ -0,0 +1,39 @@
+#include "sms_spi.h"
+
+void spi_init(SPI *spi, Tristate *TH, Tristate *TR, EXCH spixfn)
+{
+    spi->TH = TH;
+    spi->TR = TR;
+    spi->lastTH = *TH;
+    spi->bitcnt = 0;
+    spi->bit = false;
+    spi->rx = 0;
+    spi->tx = 0xff;
+    spi->spixfn = spixfn;
+}
+
+byte spi_rd(SPI *spi)
+{
+
+    return (byte)spi->bit; // return in bit 0
+}
+
+void spi_pulse(SPI *spi)
+{
+    if (*spi->TH != spi->lastTH) {
+        spi->lastTH = *spi->TH;
+        if (spi->lastTH == TRI_HIGH) {
+            spi->rx <<= 1;
+            if (*spi->TR == TRI_HIGH) {
+                spi->rx++;
+            }
+            spi->bit = spi->tx >> 7;
+            spi->tx <<= 1;
+            spi->bitcnt++;
+            if (spi->bitcnt == 8) {
+                spi->tx = spi->spixfn(spi->rx);
+                spi->bitcnt = 0;
+            }
+        }
+    }
+}

emul/z80/sms_spi.h

@@ -0,0 +1,30 @@
+#include "emul.h"
+
+/* This emulates a SPI device being connected directly on a controller port.
+
+   TH and TR control CLK and DI, input bit 0 (BTN_UP) is DO.
+
+   This device has to "pulse" frequently so that it checks whether there's
+   been a change in CLK.
+
+   We have a bit of a challenge here with regards to an important limitation
+   of the SMS: only 2 pins can be set as output. Without the ability to
+   programatically select the SPI slave, we have to keep it selected at all
+   times. This makes us vulnerable to going out of sync. This is a known
+   limitation, the user will have to re-insert the SD card when that happens.
+*/
+
+typedef struct {
+    Tristate *TH; // CLK
+    Tristate *TR; // DI
+    Tristate lastTH; // value of TH on last pulse
+    byte bitcnt; // current xchange bit count
+    bool bit; // bit to return in spi_rd()
+    byte rx;
+    byte tx;
+    EXCH spixfn;
+} SPI;
+
+void spi_init(SPI *spi, Tristate *TH, Tristate *TR, EXCH spixfn);
+byte spi_rd(SPI *spi); // for sms_ports' portX_rd
+void spi_pulse(SPI *spi);

recipes/sms/blk/622

@@ -0,0 +1,12 @@
+: (spie) DROP ; ( always enabled )
+: (spix) ( x -- x, for port B )
+    0 SWAP ( rx tx ) 8 0 DO
+        ( send bit 7 to bit 6, TR's output bit )
+        DUP 1 RSHIFT 0x40 AND ( rx tx bits ) 0x80 OR ( CLK hi )
+        0x3f PC@ OR 0xf3 AND ( TH and TR output )
+        DUP 0x3f PC! ( rx tx bits )
+        ( CLK low ) 0x7f AND 0x3f PC! ( rx tx )
+        ( shift tx ) 1 LSHIFT ( rx tx<< )
+        ( read into rx ) SWAP 1 LSHIFT 0xdc PC@ ( tx<< rx<< x )
+        ( out bit is the 6th ) 6 RSHIFT 1 AND OR
+    SWAP LOOP ( rx tx ) DROP ;