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Posted to commits@nuttx.apache.org by pk...@apache.org on 2022/06/21 14:58:16 UTC
[incubator-nuttx] branch master updated: stm32xx: Fix RTC drift when using HSE
This is an automated email from the ASF dual-hosted git repository.
pkarashchenko pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/incubator-nuttx.git
The following commit(s) were added to refs/heads/master by this push:
new 19fd0a5587 stm32xx: Fix RTC drift when using HSE
19fd0a5587 is described below
commit 19fd0a55877fa7997d88d14dde09df6cc18fd084
Author: Alan Carvalho de Assis <ac...@gmail.com>
AuthorDate: Tue Jun 21 10:10:09 2022 -0300
stm32xx: Fix RTC drift when using HSE
When using HSE to clock RTC NuttX internal time is gaining 5.5 second per
minute. Problem was NuttX using 7182 for one of the RTC division factors,
it should have been 7812. The incorrect factors used are 7182 and 0xff.
These are used in 3-4 places within Nuttx and other places as 7812 and 0xff.
However, the STMicro app note AN4759 suggests using 7999 and 124, which is
what I've used.
Explanation: These 2 factors are used to divide the HSE clock (which at this
point is 1 MHz) to 1 Hz for the RTC hardware.
To test the 2 factors, add 1 to both numbers and multiply them together.
The result needs to be as close as possible to 1 MHz.
The suggested values of 7999 and 124 => 8000*125 = 1,000,000, the prime
factors. So, the best fix for Nuttx would be these values.
Issue discovered and fixed by Peter Moody
---
arch/arm/src/stm32/stm32_rtcc.c | 8 ++++----
arch/arm/src/stm32/stm32f40xxx_rtcc.c | 8 ++++----
arch/arm/src/stm32f7/stm32_rtc.c | 8 ++++----
arch/arm/src/stm32h7/stm32_rtc.c | 8 ++++----
4 files changed, 16 insertions(+), 16 deletions(-)
diff --git a/arch/arm/src/stm32/stm32_rtcc.c b/arch/arm/src/stm32/stm32_rtcc.c
index 4e8be5a5ac..24091b659d 100644
--- a/arch/arm/src/stm32/stm32_rtcc.c
+++ b/arch/arm/src/stm32/stm32_rtcc.c
@@ -415,12 +415,12 @@ static int rtc_setup(void)
/* Configure RTC pre-scaler with the required values */
#ifdef CONFIG_STM32_RTC_HSECLOCK
- /* For a 1 MHz clock this yields 0.9999360041 Hz on the second
- * timer - which is pretty close.
+ /* STMicro app note AN4759 suggests using 7999 and 124 to
+ * get exactly 1MHz when using the RTC at 8MHz.
*/
- putreg32(((uint32_t)7182 << RTC_PRER_PREDIV_S_SHIFT) |
- ((uint32_t)0x7f << RTC_PRER_PREDIV_A_SHIFT),
+ putreg32(((uint32_t)7999 << RTC_PRER_PREDIV_S_SHIFT) |
+ ((uint32_t)124 << RTC_PRER_PREDIV_A_SHIFT),
STM32_RTC_PRER);
#else
/* Correct values for 32.768 KHz LSE clock and inaccurate LSI clock */
diff --git a/arch/arm/src/stm32/stm32f40xxx_rtcc.c b/arch/arm/src/stm32/stm32f40xxx_rtcc.c
index 5ad9228aba..4a04586e39 100644
--- a/arch/arm/src/stm32/stm32f40xxx_rtcc.c
+++ b/arch/arm/src/stm32/stm32f40xxx_rtcc.c
@@ -483,12 +483,12 @@ static int rtc_setup(void)
/* Configure RTC pre-scaler with the required values */
#ifdef CONFIG_STM32_RTC_HSECLOCK
- /* For a 1 MHz clock this yields 0.9999360041 Hz on the second
- * timer - which is pretty close.
+ /* STMicro app note AN4759 suggests using 7999 and 124 to
+ * get exactly 1MHz when using the RTC at 8MHz.
*/
- putreg32(((uint32_t)7182 << RTC_PRER_PREDIV_S_SHIFT) |
- ((uint32_t)0x7f << RTC_PRER_PREDIV_A_SHIFT),
+ putreg32(((uint32_t)7999 << RTC_PRER_PREDIV_S_SHIFT) |
+ ((uint32_t)124 << RTC_PRER_PREDIV_A_SHIFT),
STM32_RTC_PRER);
#else
/* Correct values for 32.768 KHz LSE clock and inaccurate LSI clock */
diff --git a/arch/arm/src/stm32f7/stm32_rtc.c b/arch/arm/src/stm32f7/stm32_rtc.c
index 30618d91bd..3d30a3dce9 100644
--- a/arch/arm/src/stm32f7/stm32_rtc.c
+++ b/arch/arm/src/stm32f7/stm32_rtc.c
@@ -490,12 +490,12 @@ static int rtc_setup(void)
/* Configure RTC pre-scaler with the required values */
#ifdef CONFIG_STM32F7_RTC_HSECLOCK
- /* For a 1 MHz clock this yields 0.9999360041 Hz on the second
- * timer - which is pretty close.
+ /* STMicro app note AN4759 suggests using 7999 and 124 to
+ * get exactly 1MHz when using the RTC at 8MHz.
*/
- putreg32(((uint32_t)7182 << RTC_PRER_PREDIV_S_SHIFT) |
- ((uint32_t)0x7f << RTC_PRER_PREDIV_A_SHIFT),
+ putreg32(((uint32_t)7999 << RTC_PRER_PREDIV_S_SHIFT) |
+ ((uint32_t)124 << RTC_PRER_PREDIV_A_SHIFT),
STM32_RTC_PRER);
#else
/* Correct values for 32.768 KHz LSE clock and inaccurate LSI clock */
diff --git a/arch/arm/src/stm32h7/stm32_rtc.c b/arch/arm/src/stm32h7/stm32_rtc.c
index 3d77b1b3e8..a826e0c9bf 100644
--- a/arch/arm/src/stm32h7/stm32_rtc.c
+++ b/arch/arm/src/stm32h7/stm32_rtc.c
@@ -490,12 +490,12 @@ static int rtc_setup(void)
/* Configure RTC pre-scaler with the required values */
#ifdef CONFIG_STM32H7_RTC_HSECLOCK
- /* For a 1 MHz clock this yields 0.9999360041 Hz on the second
- * timer - which is pretty close.
+ /* STMicro app note AN4759 suggests using 7999 and 124 to
+ * get exactly 1MHz when using the RTC at 8MHz.
*/
- putreg32(((uint32_t)7182 << RTC_PRER_PREDIV_S_SHIFT) |
- ((uint32_t)0x7f << RTC_PRER_PREDIV_A_SHIFT),
+ putreg32(((uint32_t)7999 << RTC_PRER_PREDIV_S_SHIFT) |
+ ((uint32_t)124 << RTC_PRER_PREDIV_A_SHIFT),
STM32_RTC_PRER);
#else
/* Correct values for 32.768 KHz LSE clock and inaccurate LSI clock */