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, 10 insertions, 0 deletions

diff --git a/timer.h b/timer.h
new file mode 100644
index 0000000..2f2e4b3
--- /dev/null
+++ b/timer.h
@@ -0,0 +1,10 @@
+#pragma once
+
+#include <stdint.h>
+
+struct timer {
+	void (*init)(void);
+	uint16_t (*get_time)(void);
+};
+
+void get_system_timer(struct timer *);