code: plan9front

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games/gb: crude serial port emulation

Timing is not as good as it needs to be,
but servicable in more forgiving scenarios.
Clock drift between two paired systems sits
around 8 - 32 cycles when tested locally.

--- a/sys/man/1/nintendo

+++ b/sys/man/1/nintendo

@@ -12,6 +12,9 @@

 ] [

 .B -x

 .I scale

+] [

+.B -li

+.I addr

 ]

 .I romfile

 .br

@@ -103,6 +106,14 @@

 .TP

 .BI -C nnnnnn,nnnnnn,nnnnnn,nnnnnn

 Select a color palette. Has no effect on roms in color mode. The syntax is of the form -C ffffff,aaaaaa,555555,000000 (using HTML style rrggbb notation).

+.TP

+.BI -li addr

+These enable serial port connectivity emulation using the network. The

+.B -l

+flag configures the listening partner, whereas

+.B -i

+configures the dialing partner. The connection is established before the rom starts.

+Communication is synchronous, emulation will stall while waiting for the other partner.

 .PP

 .B gba

 options:

@@ -163,6 +174,8 @@

 scaling.

 .br

 All emulators assume a North American (i.e. NTSC) system. PAL games (and in some cases Japanese games) are not supported.

+.br

+The serial link emulation has issues with desynchronization in timing dependent scenarios.

 .SH HISTORY

 .I Gb

 first appeared in 9front (April, 2012).

--- a/sys/src/games/gb/dat.h

+++ b/sys/src/games/gb/dat.h

@@ -151,6 +151,6 @@

 };

 #define VAR(a) {&a, sizeof(a), 1}

 #define ARR(a) {a, sizeof(*a), nelem(a)}

-enum { NEVENT = 8 };

+enum { NEVENT = 9 };

 extern int (*mapper)(int, int);

 extern u32int moncols[4];

--- a/sys/src/games/gb/ev.c

+++ b/sys/src/games/gb/ev.c

@@ -6,7 +6,8 @@

 Event evhblank, evtimer, evenv;

 extern Event evsamp, chev[4];

-Event *events[NEVENT] = {&evhblank, &evtimer, &evenv, &evsamp, &chev[0], &chev[1], &chev[2], &chev[3]};

+extern Event evse;

+Event *events[NEVENT] = {&evhblank, &evtimer, &evenv, &evsamp, &chev[0], &chev[1], &chev[2], &chev[3], &evse};

 Event *elist;

 static int timshtab[4] = {10, 4, 6, 8}, timsh;

 ulong timclock;

--- a/sys/src/games/gb/fns.h

+++ b/sys/src/games/gb/fns.h

@@ -26,3 +26,5 @@

 u8int waveread(u8int);

 void wavewrite(u8int, u8int);

 u8int timread(void);

+void serialwrite(void);

+void serialinit(int, char *);

--- a/sys/src/games/gb/gb.c

+++ b/sys/src/games/gb/gb.c

@@ -262,6 +262,8 @@

 threadmain(int argc, char **argv)

 {

 	int t;

+	int lis = -1;

+	char *addr = nil;

 	colinit();

 	ARGBEGIN {

@@ -280,11 +282,22 @@

 	case 'x':

 		fixscale = strtol(EARGF(usage()), nil, 0);

 		break;

+	case 'l':

+		lis = 1;

+		addr = EARGF(usage());

+		break;

+	case 'i':

+		lis = 0;

+		addr = EARGF(usage());

+		break;

 	default:

 		usage();

 	} ARGEND;

 	if(argc < 1)

 		usage();

+

+	if(lis == 0 || lis == 1)

+		serialinit(lis, addr);

 	loadrom(argv[0]);

 	initemu(PICW, PICH, 4, XRGB32, 1, nil);

--- a/sys/src/games/gb/mem.c

+++ b/sys/src/games/gb/mem.c

@@ -83,7 +83,11 @@

 	switch(a){

 	case JOYP: v |= 0xcf; break;

-	case SC: v |= 0x7c; break;

+	case SC:

+		if((reg[a] & 0x80) == 0 && (v & 0x80))

+			serialwrite();

+		reg[a] = v;

+		return;

 	case DIV:

 		divclock = clock;

 		v = 0;

--- a/sys/src/games/gb/mkfile

+++ b/sys/src/games/gb/mkfile

@@ -11,6 +11,7 @@

 	state.$O\

 	apu.$O\

 	eui.$O\

+	serial.$O\

 HFILES=dat.h fns.h

--- /dev/null

+++ b/sys/src/games/gb/serial.c

@@ -1,0 +1,142 @@

+#include <u.h>

+#include <libc.h>

+#include <thread.h>

+#include "../eui.h"

+#include "dat.h"

+#include "fns.h"

+

+static int infd = -1;

+static int outfd = -1;

+static int leader = 0;

+

+static Channel *inc = nil;

+static Channel *outc = nil;

+

+typedef struct Msg Msg;

+struct Msg {

+	u8int c;

+	u8int b;

+	u32int t;

+};

+

+enum{

+	Cex = 1,

+	Csync = 2,

+	Cgone = 0xFF,

+};

+

+static Msg mine = {Cgone};

+static Msg theirs = {Cgone};

+Event evse;

+

+static void

+writer(void *)

+{

+	Msg m;

+	uchar buf[1+1+4];

+

+	while(recv(outc, &m) == 1){

+		buf[0] = m.c;

+		buf[1] = m.b;

+		buf[2] = m.t>>24;

+		buf[3] = m.t>>16;

+		buf[4] = m.t>>8;

+		buf[5] = m.t;

+		if(write(outfd, buf, sizeof buf) != sizeof buf)

+			break;

+	}

+

+	chanclose(outc);

+	threadexits(nil);

+}

+

+static void

+reader(void *)

+{

+	Msg m;

+	uchar buf[1+1+4];

+

+	while(readn(infd, buf, sizeof buf) == sizeof buf){

+		m.c = buf[0];

+		m.b = buf[1];

+		m.t = ((u32int)buf[2]<<24) | ((u32int)buf[3]<<16) | ((u32int)buf[4]<<8) | (u32int)buf[5];

+		send(inc, &m);

+	}

+

+	chanclose(inc);

+	threadexits(nil);

+}

+

+void

+serialwrite(void)

+{

+	if(outc == nil)

+		return;

+	mine = (Msg){Cex, reg[SB], clock};

+}

+

+void

+serialtick(void *)

+{

+	Msg m, t;

+

+	if(leader){

+		m = (Msg){mine.c == Cgone ? Csync : mine.c, mine.b, clock};

+		if(send(outc, &m) != 1)

+			return;

+		if(recv(inc, &t) != 1)

+			return;

+		theirs = t;

+	} else {

+		if(recv(inc, &t) != 1)

+			return;

+		theirs = t;

+		m = (Msg){theirs.c, reg[SB], clock};

+		if(send(outc, &m) != 1)

+			return;

+	}

+

+	addevent(&evse, FREQ / 64);

+	assert(theirs.c != Cgone);

+	if(theirs.c == Csync)

+		return;

+

+	reg[SB] = theirs.b;

+	reg[SC] &= ~0x80;

+	if(leader)

+		reg[SC] |= 0x1;

+	else

+		reg[SC] &= ~0x1;

+	reg[IF] |= 0x8;

+}

+

+void

+serialinit(int dolis, char *addr)

+{

+	int acfd, lcfd;

+	char adir[40], ldir[40];

+

+	evse.f = serialtick;

+	addevent(&evse, FREQ / 64);

+

+	if(dolis){

+		acfd = announce(addr, adir);

+		if(acfd < 0)

+			sysfatal("failed to announce: %r");

+		lcfd = listen(adir, ldir);

+		if(lcfd < 0)

+			sysfatal("failed to listen: %r");

+		infd = outfd = accept(lcfd, ldir);

+		leader = 1;

+	} else {

+		infd = outfd = dial(addr, nil, nil, nil);

+	}

+

+	if(infd < 0 || outfd < 0)

+		sysfatal("failed to establish link: %r");

+

+	inc = chancreate(sizeof(Msg), 0);

+	outc = chancreate(sizeof(Msg), 0);

+	proccreate(reader, nil, mainstacksize);

+	proccreate(writer, nil, mainstacksize);

+}