altos: Update sensor data atomically

Read data into a temp variable, block interrupts, then update the
published value.

The bug is easy to see with the HMC5883 which has to byte-swap the
output of the chip, and hence can occasionally get caught with the
wrong byte order data.

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

1 files changed, 7 insertions, 5 deletions

diff --git a/src/drivers/ao_hmc5883.c b/src/drivers/ao_hmc5883.c
index f668fb66..9f1131d6 100644
--- a/src/drivers/ao_hmc5883.c
+++ b/src/drivers/ao_hmc5883.c
@@ -126,13 +126,15 @@ struct ao_hmc5883_sample ao_hmc5883_current;
 static void
 ao_hmc5883(void)
 {
+	struct ao_hmc5883_sample	sample;
 	ao_hmc5883_setup();
 	for (;;) {
-		ao_hmc5883_sample(&ao_hmc5883_current);
-		ao_arch_critical(
-			AO_DATA_PRESENT(AO_DATA_HMC5883);
-			AO_DATA_WAIT();
-			);
+		ao_hmc5883_sample(&sample);
+		ao_arch_block_interrupts();
+		ao_hmc5883_current = sample;
+		AO_DATA_PRESENT(AO_DATA_HMC5883);
+		AO_DATA_WAIT();
+		ao_arch_release_interrupts();
 	}
 }