altos/arm: Align data so that gcc 5.4 doesn't do byte-accesses. Add -Wcast-align

Gcc 5.4.1 tracks alignment of data through assignments, so that a
uint32_t pointer which comes from byte-aligned uint8_t data:

extern uint8_t foo[];

	uint32_t	*q = (void *) foo;

Fetches and stores through this pointer are done bytewise. This is
slow (meh), but if q references a device register, things to bad very
quickly.

This patch works around this bug in the compiler by adding
__attribute__((aligned(4))) tags to some variables, or changing them
from uint8_t to uint32_t. Places doing this will now be caught as I've
added -Wcast-align to the compiler flags. That required adding (void
*) casts, after the relevant code was checked to make sure the
compiler could tell that the addresses were aligned.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/src/drivers/ao_gps_ublox.c b/src/drivers/ao_gps_ublox.c
index 22af413a..c720f802 100644
--- a/src/drivers/ao_gps_ublox.c
+++ b/src/drivers/ao_gps_ublox.c
@@ -156,7 +156,7 @@ static char __xdata *ublox_target;
 
 static void ublox_u16(uint8_t offset)
 {
-	uint16_t __xdata *ptr = (uint16_t __xdata *) (ublox_target + offset);
+	uint16_t __xdata *ptr = (uint16_t __xdata *) (void __xdata *) (ublox_target + offset);
 	uint16_t val;
 
 	val = data_byte();
@@ -175,7 +175,7 @@ static void ublox_u8(uint8_t offset)
 
 static void ublox_u32(uint8_t offset) __reentrant
 {
-	uint32_t __xdata *ptr = (uint32_t __xdata *) (ublox_target + offset);
+	uint32_t __xdata *ptr = (uint32_t __xdata *) (void __xdata *) (ublox_target + offset);
 	uint32_t val;
 
 	val = ((uint32_t) data_byte ());