libpayload: Add a timer_us() function.

This function returns the number of microseconds scaled from the number of raw
timer ticks. It accepts a base parameter which is subtracted from the current
time, which makes it easy to keep track of relative times.

Change-Id: I55f2f9e90c0e12cda430bbe88b044f12b0b563c8
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/179600
Reviewed-by: Ronald Minnich <rminnich@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit 4dd549e18d170dbf918c5b4b11bbe1f4e99b6695)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6897
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/payloads/libpayload/libc/time.c b/payloads/libpayload/libc/time.c
index ec1c85ce8c..0d8163495b 100644
--- a/payloads/libpayload/libc/time.c
+++ b/payloads/libpayload/libc/time.c
@@ -189,3 +189,20 @@ void delay(unsigned int s)
 {
 	_delay((uint64_t)s * timer_hz());
 }
+
+u64 timer_us(u64 base)
+{
+	static u64 hz;
+
+	// Only check timer_hz once. Assume it doesn't change.
+	if (hz == 0) {
+		hz = timer_hz();
+		if (hz < 1000000) {
+			printf("Timer frequency %lld is too low, "
+			       "must be at least 1MHz.\n", hz);
+			halt();
+		}
+	}
+
+	return timer_raw_value() / (hz / 1000000) - base;
+}