diff options
| author | Keith Packard <keithp@keithp.com> | 2016-12-17 20:58:36 -0800 |
|---|---|---|
| committer | Bdale Garbee <bdale@gag.com> | 2017-01-25 12:21:43 -0700 |
| commit | fe25510fc23031f1a3c1b42edd37067d1989a9f6 (patch) | |
| tree | 3cdc98d2c3d1c8d9bd95045771be7d15226d246b /src/stmf0/ao_adc_fast.h | |
| parent | 4163d88ed36ce8863218366f1fb504f7061a4ca5 (diff) | |
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>
Diffstat (limited to 'src/stmf0/ao_adc_fast.h')
| -rw-r--r-- | src/stmf0/ao_adc_fast.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/stmf0/ao_adc_fast.h b/src/stmf0/ao_adc_fast.h index b8b5e003..3f0b0547 100644 --- a/src/stmf0/ao_adc_fast.h +++ b/src/stmf0/ao_adc_fast.h @@ -28,7 +28,7 @@ ao_adc_init(void); /* Total ring size in samples */ #define AO_ADC_RING_SIZE 256 -extern uint16_t ao_adc_ring[AO_ADC_RING_SIZE]; +extern uint16_t ao_adc_ring[AO_ADC_RING_SIZE] __attribute__((aligned(4))); #define ao_adc_ring_step(pos,inc) (((pos) + (inc)) & (AO_ADC_RING_SIZE - 1)) |