Use more generic interface for barometer and timer

This patch abstracts the global symbols for getting barometer readings behind
a "struct of function pointers" interface as popular in Linux Kernel, U-Boot
and others. This means that unit testing can take place with mocked hardware
peripherals. The old "global" drivers are still available, behind explicit
function calls required to access the now-static functions.

This patch also introduces a timer peripheral software module with the same
model, to support future unit testing of altitude rate etc.

1 files changed, 12 insertions, 2 deletions

diff --git a/barometer_sim.c b/barometer_sim.c
index c695590..5c5b7d4 100644
--- a/barometer_sim.c
+++ b/barometer_sim.c
@@ -1,3 +1,5 @@
+#include "barometer.h"
+
 /* Dummy pressures to return in sequence, each call to barometer_read */
 static const float pressures[] = {
 	1019.5,
@@ -15,13 +17,21 @@ static const float pressures[] = {
 };
 static int cursor = 0;
 
-void barometer_init(void)
+static void barometer_init(void)
 {
 	cursor = 0;
 }
 
-float barometer_read(void)
+static float barometer_read(void)
 {
 	cursor %= sizeof(pressures)/sizeof(pressures[0]);
 	return pressures[cursor++];
 }
+
+/**/
+
+void get_system_barometer(struct barometer *barometer)
+{
+	barometer->init = barometer_init;
+	barometer->read_pressure = barometer_read;
+}