altos: add ao_time_ns API

This provides nano-second resolution times by reading the systick
value (which runs at 250ns ticks on stm).

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/stmf0/ao_timer.c b/src/stmf0/ao_timer.c
index 1def5f69..58e52995 100644
--- a/src/stmf0/ao_timer.c
+++ b/src/stmf0/ao_timer.c
@@ -35,6 +35,22 @@ ao_time(void)
 	return ao_tick_count;
 }
 
+uint64_t
+ao_time_ns(void)
+{
+	AO_TICK_TYPE	before, after;
+	uint32_t	cvr;
+
+	do {
+		before = ao_tick_count;
+		cvr = stm_systick.cvr;
+		after = ao_tick_count;
+	} while (before != after);
+
+	return (uint64_t) after * (1000000000ULL / AO_HERTZ) +
+		(uint64_t) cvr * (1000000000ULL / AO_SYSTICK);
+}
+
 #if AO_DATA_ALL
 volatile uint8_t	ao_data_interval = 1;
 volatile uint8_t	ao_data_count;