[timer] Formalise the timer API

We now have two implementations for the timer API: one using the
time-of-day counter at 40:70 and one using RDTSC.  Both make use of
timer2_udelay().

src/arch/i386/core/rdtsc_timer.c

@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+/** @file
+ *
+ * RDTSC timer
+ *
+ */
+
+#include <assert.h>
+#include <gpxe/timer.h>
+#include <gpxe/timer2.h>
+
+/**
+ * Number of TSC ticks per microsecond
+ *
+ * This is calibrated on the first use of the timer.
+ */
+static unsigned long rdtsc_ticks_per_usec;
+
+/**
+ * Delay for a fixed number of microseconds
+ *
+ * @v usecs		Number of microseconds for which to delay
+ */
+static void rdtsc_udelay ( unsigned long usecs ) {
+	unsigned long start;
+	unsigned long elapsed;
+
+	/* Sanity guard, since we may divide by this */
+	if ( ! usecs )
+		usecs = 1;
+
+	start = currticks();
+	if ( rdtsc_ticks_per_usec ) {
+		/* Already calibrated; busy-wait until done */
+		do {
+			elapsed = ( currticks() - start );
+		} while ( elapsed < ( usecs * rdtsc_ticks_per_usec ) );
+	} else {
+		/* Not yet calibrated; use timer2 and calibrate
+		 * based on result.
+		 */
+		timer2_udelay ( usecs );
+		elapsed = ( currticks() - start );
+		rdtsc_ticks_per_usec = ( elapsed / usecs );
+		DBG ( "RDTSC timer calibrated: %ld ticks in %ld usecs "
+		      "(%ld MHz)\n", elapsed, usecs,
+		      ( rdtsc_ticks_per_usec << TSC_SHIFT ) );
+	}
+}
+
+/**
+ * Get number of ticks per second
+ *
+ * @ret ticks_per_sec	Number of ticks per second
+ */
+static unsigned long rdtsc_ticks_per_sec ( void ) {
+
+	/* Calibrate timer, if not already done */
+	if ( ! rdtsc_ticks_per_usec )
+		udelay ( 1 );
+
+	/* Sanity check */
+	assert ( rdtsc_ticks_per_usec != 0 );
+
+	return ( rdtsc_ticks_per_usec * 1000 * 1000 );
+}
+
+PROVIDE_TIMER ( rdtsc, udelay, rdtsc_udelay );
+PROVIDE_TIMER_INLINE ( rdtsc, currticks );
+PROVIDE_TIMER ( rdtsc, ticks_per_sec, rdtsc_ticks_per_sec );