cpu/allwinner/a10: Implement udelay using timer 0

Change-Id: I4825f0d57696cd28751c59ae133b7e3315fb78e5
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/4595
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: David Hendricks <dhendrix@chromium.org>

1 files changed, 39 insertions, 3 deletions

diff --git a/src/cpu/allwinner/a10/timer.c b/src/cpu/allwinner/a10/timer.c
index e156398be3..60cc60c4d1 100644
--- a/src/cpu/allwinner/a10/timer.c
+++ b/src/cpu/allwinner/a10/timer.c
@@ -1,19 +1,55 @@
 /*
- * Placeholder for code to come(needed to complete build)
+ * Timer control and delays for Allwinner CPUs
  *
  * Copyright (C) 2013  Alexandru Gagniuc <mr.nuke.me@gmail.com>
  * Subject to the GNU GPL v2, or (at your option) any later version.
  */
 
+#include "timer.h"
+
+#include <arch/io.h>
 #include <delay.h>
 #include <timer.h>
 
+struct a1x_timer *const tmr0 =
+		&((struct a1x_timer_module *)A1X_TIMER_BASE)->timer[0];
+
+static inline u32 read_timer(void)
+{
+	return read32(&tmr0->val);
+}
+
 void init_timer(void)
 {
-	/* Stub */
+	u32 reg32;
+	/* Load the timer rollover value */
+	write32(0xffffffff, &tmr0->interval);
+	/* Configure the timer to run from 24MHz oscillator, no prescaler */
+	reg32 = TIMER_CTRL_PRESC_DIV_EXP(0);
+	reg32 |= TIMER_CTRL_CLK_SRC_OSC24M;
+	reg32 |= TIMER_CTRL_RELOAD;
+	reg32 |= TIMER_CTRL_TMR_EN;
+	write32(reg32, &tmr0->ctrl);
 }
 
 void udelay(unsigned usec)
 {
-	/* Stub */
+	u32 curr_tick, last_tick;
+	s32 ticks_left;
+
+	last_tick = read_timer();
+	/* 24 timer ticks per microsecond (24 MHz, divided by 1) */
+	ticks_left = usec * 24;
+
+	/* FIXME: Should we consider timer rollover?
+	 * From when we start the timer, we have almost three minutes before it
+	 * rolls over, so we should be long into having booted our payload.
+	 */
+	while (ticks_left > 0) {
+		curr_tick = read_timer();
+		/* Timer value decreases with each tick */
+		ticks_left -= last_tick - curr_tick;
+		last_tick = curr_tick;
+	}
+
 }