summaryrefslogtreecommitdiff
path: root/chip
diff options
context:
space:
mode:
authorShawn Nematbakhsh <shawnn@chromium.org>2015-02-27 16:05:54 -0800
committerChromeOS Commit Bot <chromeos-commit-bot@chromium.org>2015-02-28 03:46:35 +0000
commitd1939ee10155af38a869e5315e6374af73200e5f (patch)
tree05ca7c8f260a12c87d73492fa9f18f33f39f4ffc /chip
parent8fe9304ae24d736698f8c7d02b299b8c815de91f (diff)
downloadchrome-ec-d1939ee10155af38a869e5315e6374af73200e5f.tar.gz
stm32f0: Fix RTC read glitch
Reads to RTC_SSR may be invalid if they occur close to the RTCCLK edge. As suggested by the datasheet, perform consecutive identical reads to ensure the read is valid. BUG=chrome-os-partner:37216 TEST=Manual on Samus. Repeatedly call rtc_read in test function, verify that RTC_SSR never incorrectly ticks up. BRANCH=Samus Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org> Change-Id: Ib26fbfab4a07263f638c580066e993675dd8c451 Reviewed-on: https://chromium-review.googlesource.com/254725 Reviewed-by: Alec Berg <alecaberg@chromium.org>
Diffstat (limited to 'chip')
-rw-r--r--chip/stm32/clock-stm32f0.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/chip/stm32/clock-stm32f0.c b/chip/stm32/clock-stm32f0.c
index fe474fe326..3586b64a5c 100644
--- a/chip/stm32/clock-stm32f0.c
+++ b/chip/stm32/clock-stm32f0.c
@@ -131,7 +131,13 @@ static inline void rtc_read(uint32_t *rtc, uint32_t *rtcss)
/* Read current time synchronously */
do {
*rtc = STM32_RTC_TR;
- *rtcss = STM32_RTC_SSR;
+ /*
+ * RTC_SSR must be read twice with identical values because
+ * glitches may occur for reads close to the RTCCLK edge.
+ */
+ do {
+ *rtcss = STM32_RTC_SSR;
+ } while (*rtcss != STM32_RTC_SSR);
} while (*rtc != STM32_RTC_TR);
}