add rtc3231

Reference: /n/atom/patch/applied/pirtc3231
Date: Sun Jan 10 18:32:32 CET 2016
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/bcm/devrtc3231.c	Thu Jan  1 00:00:00 1970
+++ /sys/src/9/bcm/devrtc3231.c	Sun Jan 10 18:32:25 2016
@@ -0,0 +1,343 @@
+/*
+ * Maxim DS3231 realtime clock (accessed via rtc)
+ */
+
+#include	"u.h"
+#include	"../port/lib.h"
+#include	"mem.h"
+#include	"dat.h"
+#include	"fns.h"
+#include	"../port/error.h"
+
+enum {
+	/* DS3231 registers */
+	Seconds=	0,
+	Minutes=	1,
+	Hours=		2,
+	Weekday=	3,
+	Mday=		4,
+	Month=		5,
+	Year=		6,
+	Nbcd=		7,
+
+	/* Hours register may be in 12-hour or 24-hour mode */
+	Twelvehr=	1<<6,
+	Pm=		1<<5,
+
+	I2Caddr=	0x68,
+	
+};
+
+typedef struct Rtc	Rtc;
+
+struct Rtc
+{
+	int	sec;
+	int	min;
+	int	hour;
+	int	mday;
+	int	mon;
+	int	year;
+};
+
+enum{
+	Qdir = 0,
+	Qrtc,
+};
+
+Dirtab rtcdir[]={
+	".",	{Qdir, 0, QTDIR},	0,	0555,
+	"rtc",		{Qrtc, 0},	0,	0664,
+};
+
+static ulong rtc2sec(Rtc*);
+static void sec2rtc(ulong, Rtc*);
+
+static Chan*
+rtcattach(char* spec)
+{
+	return devattach('r', spec);
+}
+
+static Walkqid*	 
+rtcwalk(Chan* c, Chan *nc, char** name, int nname)
+{
+	return devwalk(c, nc, name, nname, rtcdir, nelem(rtcdir), devgen);
+}
+
+static int	 
+rtcstat(Chan* c, uchar* dp, int n)
+{
+	return devstat(c, dp, n, rtcdir, nelem(rtcdir), devgen);
+}
+
+static Chan*
+rtcopen(Chan* c, int omode)
+{
+	char dummy;
+
+	omode = openmode(omode);
+	switch((ulong)c->qid.path){
+	case Qrtc:
+		if(strcmp(up->user, eve)!=0 && omode!=OREAD)
+			error(Eperm);
+		/* if it's not there, this will throw an error */
+		i2cread(I2Caddr, &dummy, 1);
+		break;
+	}
+	return devopen(c, omode, rtcdir, nelem(rtcdir), devgen);
+}
+
+static void	 
+rtcclose(Chan*)
+{
+}
+
+static int
+bcd(int n)
+{
+	return (n & 0xF) + (10 * (n >> 4));
+}
+
+long	 
+rtctime(void)
+{
+	uchar clk[Nbcd];
+	Rtc rtc;
+
+	clk[0] = 0;
+	i2cwrite(I2Caddr, clk, 1);
+	i2cread(I2Caddr, clk, Nbcd);
+
+	/*
+	 *  convert from BCD
+	 */
+	rtc.sec = bcd(clk[Seconds]);
+	rtc.min = bcd(clk[Minutes]);
+	rtc.hour = bcd(clk[Hours]);
+	if(clk[Hours] & Twelvehr){
+		rtc.hour = bcd(clk[Hours] & 0x1F);
+		if(clk[Hours] & Pm)
+			rtc.hour += 12;
+	}
+	rtc.mday = bcd(clk[Mday]);
+	rtc.mon = bcd(clk[Month] & 0x1F);
+	rtc.year = bcd(clk[Year]);
+
+	/*
+	 *  the world starts jan 1 1970
+	 */
+	if(rtc.year < 70)
+		rtc.year += 2000;
+	else
+		rtc.year += 1900;
+	return rtc2sec(&rtc);
+}
+
+
+static long	 
+rtcread(Chan* c, void* buf, long n, vlong off)
+{
+	ulong t;
+	ulong offset = off;
+
+	if(c->qid.type & QTDIR)
+		return devdirread(c, buf, n, rtcdir, nelem(rtcdir), devgen);
+
+	switch((ulong)c->qid.path){
+	case Qrtc:
+		t = rtctime();
+		n = readnum(offset, buf, n, t, 12);
+		return n;
+	}
+	error(Ebadarg);
+	return 0;
+}
+
+#define PUTBCD(n,o) bcdclock[1+o] = (n % 10) | (((n / 10) % 10)<<4)
+
+static long	 
+rtcwrite(Chan* c, void* buf, long n, vlong off)
+{
+	Rtc rtc;
+	ulong secs;
+	uchar bcdclock[1+Nbcd];
+	char *cp, *ep;
+	ulong offset = off;
+
+	if(offset!=0)
+		error(Ebadarg);
+
+
+	switch((ulong)c->qid.path){
+	case Qrtc:
+		/*
+		 *  read the time
+		 */
+		cp = ep = buf;
+		ep += n;
+		while(cp < ep){
+			if(*cp>='0' && *cp<='9')
+				break;
+			cp++;
+		}
+		secs = strtoul(cp, 0, 0);
+	
+		/*
+		 *  convert to bcd
+		 */
+		sec2rtc(secs, &rtc);
+		PUTBCD(rtc.sec, Seconds);
+		PUTBCD(rtc.min, Minutes);	/* forces 24 hour mode */
+		PUTBCD(rtc.hour, Hours);
+		PUTBCD(0, Weekday);		/* hope no other OS uses this */
+		PUTBCD(rtc.mday, Mday);
+		PUTBCD(rtc.mon, Month);
+		PUTBCD(rtc.year, Year);
+
+		/*
+		 *  write the clock
+		 */
+		bcdclock[0] = 0;
+		i2cwrite(I2Caddr, bcdclock, 1+Nbcd);
+		return n;
+	}
+	error(Ebadarg);
+	return 0;
+}
+
+Dev rtc3231devtab = {
+	'r',
+	"rtc",
+
+	devreset,
+	devinit,
+	devshutdown,
+	rtcattach,
+	rtcwalk,
+	rtcstat,
+	rtcopen,
+	devcreate,
+	rtcclose,
+	rtcread,
+	devbread,
+	rtcwrite,
+	devbwrite,
+	devremove,
+	devwstat,
+};
+
+#define SEC2MIN 60L
+#define SEC2HOUR (60L*SEC2MIN)
+#define SEC2DAY (24L*SEC2HOUR)
+
+/*
+ *  days per month plus days/year
+ */
+static	int	dmsize[] =
+{
+	365, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
+};
+static	int	ldmsize[] =
+{
+	366, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
+};
+
+/*
+ *  return the days/month for the given year
+ */
+static int*
+yrsize(int y)
+{
+	if((y%4) == 0 && ((y%100) != 0 || (y%400) == 0))
+		return ldmsize;
+	else
+		return dmsize;
+}
+
+/*
+ *  compute seconds since Jan 1 1970
+ */
+static ulong
+rtc2sec(Rtc *rtc)
+{
+	ulong secs;
+	int i;
+	int *d2m;
+
+	secs = 0;
+
+	/*
+	 *  seconds per year
+	 */
+	for(i = 1970; i < rtc->year; i++){
+		d2m = yrsize(i);
+		secs += d2m[0] * SEC2DAY;
+	}
+
+	/*
+	 *  seconds per month
+	 */
+	d2m = yrsize(rtc->year);
+	for(i = 1; i < rtc->mon; i++)
+		secs += d2m[i] * SEC2DAY;
+
+	secs += (rtc->mday-1) * SEC2DAY;
+	secs += rtc->hour * SEC2HOUR;
+	secs += rtc->min * SEC2MIN;
+	secs += rtc->sec;
+
+	return secs;
+}
+
+/*
+ *  compute rtc from seconds since Jan 1 1970
+ */
+static void
+sec2rtc(ulong secs, Rtc *rtc)
+{
+	int d;
+	long hms, day;
+	int *d2m;
+
+	/*
+	 * break initial number into days
+	 */
+	hms = secs % SEC2DAY;
+	day = secs / SEC2DAY;
+	if(hms < 0) {
+		hms += SEC2DAY;
+		day -= 1;
+	}
+
+	/*
+	 * generate hours:minutes:seconds
+	 */
+	rtc->sec = hms % 60;
+	d = hms / 60;
+	rtc->min = d % 60;
+	d /= 60;
+	rtc->hour = d;
+
+	/*
+	 * year number
+	 */
+	if(day >= 0)
+		for(d = 1970; day >= *yrsize(d); d++)
+			day -= *yrsize(d);
+	else
+		for (d = 1970; day < 0; d--)
+			day += *yrsize(d-1);
+	rtc->year = d;
+
+	/*
+	 * generate month
+	 */
+	d2m = yrsize(rtc->year);
+	for(d = 1; day >= d2m[d]; d++)
+		day -= d2m[d];
+	rtc->mday = day + 1;
+	rtc->mon = d;
+
+	return;
+}