[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/include/bios.h

@@ -5,7 +5,6 @@
 #define BDA_FBMS 0x0013
 #define BDA_NUM_DRIVES 0x0075
 
-extern unsigned long currticks ( void );
 extern void cpu_nap ( void );
 
 #endif /* BIOS_H */

src/arch/i386/include/bits/timer.h

@@ -0,0 +1,13 @@
+#ifndef _BITS_TIMER_H
+#define _BITS_TIMER_H
+
+/** @file
+ *
+ * i386-specific timer API implementations
+ *
+ */
+
+#include <gpxe/bios_timer.h>
+#include <gpxe/rdtsc_timer.h>
+
+#endif /* _BITS_TIMER_H */

src/arch/i386/include/bits/timer2.h

@@ -1,8 +0,0 @@
-#ifndef BITS_TIMER2_H
-#define BITS_TIMER2_H
-
-#include <stddef.h>
-
-void i386_timer2_udelay(unsigned int usecs);
-
-#endif

src/arch/i386/include/gpxe/bios_timer.h

@@ -0,0 +1,42 @@
+#ifndef _GPXE_BIOS_TIMER_H
+#define _GPXE_BIOS_TIMER_H
+
+/** @file
+ *
+ * BIOS timer
+ *
+ */
+
+#ifdef TIMER_PCBIOS
+#define TIMER_PREFIX_pcbios
+#else
+#define TIMER_PREFIX_pcbios __pcbios_
+#endif
+
+#include <gpxe/timer2.h>
+
+/**
+ * Delay for a fixed number of microseconds
+ *
+ * @v usecs		Number of microseconds for which to delay
+ */
+static inline __always_inline void
+TIMER_INLINE ( pcbios, udelay ) ( unsigned long usecs ) {
+	/* BIOS timer is not high-resolution enough for udelay(), so
+	 * we use timer2
+	 */
+	timer2_udelay ( usecs );
+}
+
+/**
+ * Get number of ticks per second
+ *
+ * @ret ticks_per_sec	Number of ticks per second
+ */
+static inline __always_inline unsigned long
+TIMER_INLINE ( pcbios, ticks_per_sec ) ( void ) {
+	/* BIOS timer ticks over at 18.2 ticks per second */
+	return 18;
+}
+
+#endif /* _GPXE_BIOS_TIMER_H */

src/arch/i386/include/gpxe/rdtsc_timer.h

@@ -0,0 +1,37 @@
+#ifndef _GPXE_RDTSC_TIMER_H
+#define _GPXE_RDTSC_TIMER_H
+
+/** @file
+ *
+ * RDTSC timer
+ *
+ */
+
+#ifdef TIMER_RDTSC
+#define TIMER_PREFIX_rdtsc
+#else
+#define TIMER_PREFIX_rdtsc __rdtsc_
+#endif
+
+/**
+ * RDTSC values can easily overflow an unsigned long.  We discard the
+ * low-order bits in order to obtain sensibly-scaled values.
+ */
+#define TSC_SHIFT 8
+
+/**
+ * Get current system time in ticks
+ *
+ * @ret ticks		Current time, in ticks
+ */
+static inline __always_inline unsigned long
+TIMER_INLINE ( rdtsc, currticks ) ( void ) {
+	unsigned long ticks;
+
+	__asm__ __volatile__ ( "rdtsc\n\t"
+			       "shrdl %1, %%edx, %%eax\n\t"
+			       : "=a" ( ticks ) : "i" ( TSC_SHIFT ) : "edx" );
+	return ticks;
+}
+
+#endif /* _GPXE_RDTSC_TIMER_H */

src/arch/i386/include/gpxe/timer2.h

@@ -0,0 +1,12 @@
+#ifndef _GPXE_TIMER2_H
+#define _GPXE_TIMER2_H
+
+/** @file
+ *
+ * Timer chip control
+ *
+ */
+
+extern void timer2_udelay ( unsigned long usecs );
+
+#endif /* _GPXE_TIMER2_H */