cpu/stm32f0: RTC implementation with external clock

tests: Tests for RTC clock

boards/nucleo-f091/Makefile.features

 FEATURES_PROVIDED += cpp
 FEATURES_PROVIDED += periph_cpuid
 FEATURES_PROVIDED += periph_gpio
+FEATURES_PROVIDED += periph_rtc
 FEATURES_PROVIDED += periph_uart
 FEATURES_MCU_GROUP = cortex_m0

boards/nucleo-f091/include/periph_conf.h

@@ -156,6 +156,18 @@ extern "C" {
 #define GPIO_5_IRQ          EXTI4_15_IRQn
 /** @} */
 
+/**
+ * @name RTC configuration
+ * @{
+ */
+/**
+ * Nucleos with MB1136 C-02 or MB1136 C-03 -sticker on it have the required LSE
+ * oscillator provided on the X2 slot.
+ * See Nucleo User Manual UM1724 section 5.6.2.
+ */
+#define RTC_NUMOF           (1U)
+/** @} */
+
 #ifdef __cplusplus
 }
 #endif

cpu/stm32f0/periph/rtc.c

+/*
+ * Copyright (C) 2015 Lari Lehtomäki
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     cpu_stm32f0
+ * @{
+ * @file
+ * @brief       Low-level RTC driver implementation
+ * @author      Lari Lehtomäki <lari@lehtomaki.fi>
+ * @}
+ */
+
+
+#include <time.h>
+#include "cpu.h"
+#include "periph/rtc.h"
+#include "periph_conf.h"
+#include "sched.h"
+#include "thread.h"
+
+/* guard file in case no RTC device was specified */
+#if RTC_NUMOF
+
+#define RTC_WRITE_PROTECTION_KEY1   (0xCA)
+#define RTC_WRITE_PROTECTION_KEY2   (0x53)
+#define RTC_SYNC_PRESCALER          (0xff) /**< prescaler for 32.768 kHz oscillator */
+#define RTC_ASYNC_PRESCALER         (0x7f) /**< prescaler for 32.768 kHz oscillator */
+
+#define MCU_YEAR_OFFSET              (100) /**< struct tm counts years since 1900
+                                               but RTC has only two-digit year
+                                               hence the offset of 100 years. */
+
+typedef struct {
+    rtc_alarm_cb_t cb;        /**< callback called from RTC interrupt */
+    void *arg;                /**< argument passed to the callback */
+} rtc_state_t;
+
+static rtc_state_t rtc_callback;
+
+static uint8_t byte2bcd(uint8_t value);
+
+/**
+ * @brief Initializes the RTC to use LSE (external 32.768 kHz oscillator) as a
+ * clocl source. Verify that your board has this oscillator. If other clock
+ * source is used, then also the prescaler constants should be changed.
+ */
+void rtc_init(void)
+{
+
+    /* Enable write access to RTC registers */
+    RCC->APB1ENR |= RCC_APB1ENR_PWREN;
+    PWR->CR |= PWR_CR_DBP;
+
+    /* Reset RTC domain */
+    RCC->BDCR |= RCC_BDCR_BDRST;
+    RCC->BDCR &= ~(RCC_BDCR_BDRST);
+
+    /* Enable the LSE clock (external 32.768 kHz oscillator) */
+    RCC->BDCR &= ~(RCC_BDCR_LSEON);
+    RCC->BDCR &= ~(RCC_BDCR_LSEBYP);
+    RCC->BDCR |= RCC_BDCR_LSEON;
+    while ( (RCC->BDCR & RCC_BDCR_LSERDY) == 0 );
+
+    /* Switch RTC to LSE clock source */
+    RCC->BDCR &= ~(RCC_BDCR_RTCSEL);
+    RCC->BDCR |= RCC_BDCR_RTCSEL_LSE;
+
+    /* Enable the RTC */
+    RCC->BDCR |= RCC_BDCR_RTCEN;
+
+    /* Unlock RTC write protection */
+    RTC->WPR = RTC_WRITE_PROTECTION_KEY1;
+    RTC->WPR = RTC_WRITE_PROTECTION_KEY2;
+
+    /* Enter RTC Init mode */
+    RTC->ISR = 0;
+    RTC->ISR |= RTC_ISR_INIT;
+    while ( (RTC->ISR & RTC_ISR_INITF) == 0 );
+
+    /* Set 24-h clock */
+    RTC->CR |= RTC_CR_FMT;
+    /* Timestamps enabled */
+    RTC->CR |= RTC_CR_TSE;
+
+    /* Configure the RTC PRER */
+    RTC->PRER = RTC_SYNC_PRESCALER;
+    RTC->PRER |= (RTC_ASYNC_PRESCALER << 16);
+
+    /* Exit RTC init mode */
+    RTC->ISR &= (uint32_t)~RTC_ISR_INIT;
+
+    /* Enable RTC write protection */
+    RTC->WPR = 0xff;
+
+}
+
+int rtc_set_time(struct tm *time)
+{
+    /* Enable write access to RTC registers */
+    RCC->APB1ENR |= RCC_APB1ENR_PWREN;
+    PWR->CR |= PWR_CR_DBP;
+
+    /* Unlock RTC write protection */
+    RTC->WPR = RTC_WRITE_PROTECTION_KEY1;
+    RTC->WPR = RTC_WRITE_PROTECTION_KEY2;
+
+    /* Enter RTC Init mode */
+    RTC->ISR |= RTC_ISR_INIT;
+    while ( (RTC->ISR & RTC_ISR_INITF) == 0 );
+
+
+    RTC->DR = ( (((uint32_t)byte2bcd(time->tm_year - MCU_YEAR_OFFSET) << 16) & (RTC_DR_YT | RTC_DR_YU) ) |
+                (((uint32_t)byte2bcd(time->tm_mon+1)<<  8) & (RTC_DR_MT | RTC_DR_MU) ) |
+                (((uint32_t)byte2bcd(time->tm_mday) <<  0) & (RTC_DR_DT | RTC_DR_DU) ) );
+
+    RTC->TR = ( (((uint32_t)byte2bcd(time->tm_hour) << 16) & (RTC_TR_HT | RTC_TR_HU) ) |
+                (((uint32_t)byte2bcd(time->tm_min)  <<  8) & (RTC_TR_MNT| RTC_TR_MNU)) |
+                (((uint32_t)byte2bcd(time->tm_sec)  <<  0) & (RTC_TR_ST | RTC_TR_SU) ) );
+
+    /* Exit RTC init mode */
+    RTC->ISR &= (uint32_t)~RTC_ISR_INIT;
+    /* Enable RTC write protection */
+    RTC->WPR = 0xFF;
+    return 0;
+}
+
+int rtc_get_time(struct tm *time)
+{
+    time->tm_year = MCU_YEAR_OFFSET;
+    time->tm_year +=(((RTC->DR & RTC_DR_YT)  >> 20) * 10) + ((RTC->DR & RTC_DR_YU)  >> 16);
+    time->tm_mon  = (((RTC->DR & RTC_DR_MT)  >> 12) * 10) + ((RTC->DR & RTC_DR_MU)  >>  8) - 1;
+    time->tm_mday = (((RTC->DR & RTC_DR_DT)  >>  4) * 10) + ((RTC->DR & RTC_DR_DU)  >>  0);
+    time->tm_hour = (((RTC->TR & RTC_TR_HT)  >> 20) * 10) + ((RTC->TR & RTC_TR_HU)  >> 16);
+    if ( RTC->TR & RTC_TR_PM )
+        time->tm_hour += 12;
+    time->tm_min  = (((RTC->TR & RTC_TR_MNT) >> 12) * 10) + ((RTC->TR & RTC_TR_MNU) >>  8);
+    time->tm_sec  = (((RTC->TR & RTC_TR_ST)  >>  4) * 10) + ((RTC->TR & RTC_TR_SU)  >>  0);
+    return 0;
+}
+
+int rtc_set_alarm(struct tm *time, rtc_alarm_cb_t cb, void *arg)
+{
+    /* Enable write access to RTC registers */
+    RCC->APB1ENR |= RCC_APB1ENR_PWREN;
+    PWR->CR |= PWR_CR_DBP;
+
+    /* Unlock RTC write protection */
+    RTC->WPR = RTC_WRITE_PROTECTION_KEY1;
+    RTC->WPR = RTC_WRITE_PROTECTION_KEY2;
+
+    /* Enter RTC Init mode */
+    RTC->ISR |= RTC_ISR_INIT;
+    while ( (RTC->ISR & RTC_ISR_INITF) == 0 );
+
+    RTC->CR &= ~(RTC_CR_ALRAE);
+    while ( (RTC->ISR & RTC_ISR_ALRAWF) == 0 );
+    RTC->ALRMAR &= ~(RTC_ALRMAR_MSK1 | RTC_ALRMAR_MSK2 | RTC_ALRMAR_MSK3 | RTC_ALRMAR_MSK4);
+    RTC->ALRMAR = ( (((uint32_t)byte2bcd(time->tm_mday) << 24) & (RTC_ALRMAR_DT | RTC_ALRMAR_DU) ) |
+                    (((uint32_t)byte2bcd(time->tm_hour) << 16) & (RTC_ALRMAR_HT | RTC_ALRMAR_HU) ) |
+                    (((uint32_t)byte2bcd(time->tm_min)  <<  8) & (RTC_ALRMAR_MNT| RTC_ALRMAR_MNU)) |
+                    (((uint32_t)byte2bcd(time->tm_sec)  <<  0) & (RTC_ALRMAR_ST | RTC_ALRMAR_SU) ) );
+    /* Enable Alarm A */
+    RTC->CR |= RTC_CR_ALRAE;
+    RTC->CR |= RTC_CR_ALRAIE;
+    RTC->ISR &= ~(RTC_ISR_ALRAF);
+
+    /* Exit RTC init mode */
+    RTC->ISR &= (uint32_t)~RTC_ISR_INIT;
+    /* Enable RTC write protection */
+    RTC->WPR = 0xFF;
+
+    EXTI->IMR  |= EXTI_IMR_MR17;
+    EXTI->RTSR |= EXTI_RTSR_TR17;
+    NVIC_SetPriority(RTC_IRQn, 10);
+    NVIC_EnableIRQ(RTC_IRQn);
+
+    rtc_callback.cb = cb;
+    rtc_callback.arg = arg;
+
+    return 0;
+}
+
+int rtc_get_alarm(struct tm *time)
+{
+    time->tm_year = MCU_YEAR_OFFSET;
+    time->tm_year +=(((RTC->DR     & RTC_DR_YT)      >> 20) * 10) + ((RTC->DR & RTC_DR_YU)          >> 16);
+    time->tm_mon  = (((RTC->DR     & RTC_DR_MT)      >> 12) * 10) + ((RTC->DR & RTC_DR_MU)          >>  8) - 1;
+    time->tm_mday = (((RTC->ALRMAR & RTC_ALRMAR_DT)  >> 28) * 10) + ((RTC->ALRMAR & RTC_ALRMAR_DU)  >> 24);
+    time->tm_hour = (((RTC->ALRMAR & RTC_ALRMAR_HT)  >> 20) * 10) + ((RTC->ALRMAR & RTC_ALRMAR_HU)  >> 16);
+    if ( (RTC->ALRMAR & RTC_ALRMAR_PM) && (RTC->CR & RTC_CR_FMT) )
+        time->tm_hour += 12;
+    time->tm_min  = (((RTC->ALRMAR & RTC_ALRMAR_MNT) >> 12) * 10) + ((RTC->ALRMAR & RTC_ALRMAR_MNU) >>  8);
+    time->tm_sec  = (((RTC->ALRMAR & RTC_ALRMAR_ST)  >>  4) * 10) + ((RTC->ALRMAR & RTC_ALRMAR_SU)  >>  0);
+    return 0;
+}
+
+void rtc_clear_alarm(void)
+{
+    /* Disable Alarm A */
+    RTC->CR &= RTC_CR_ALRAE;
+    RTC->CR &= RTC_CR_ALRAIE;
+
+    rtc_callback.cb = NULL;
+    rtc_callback.arg = NULL;
+}
+
+void rtc_poweron(void)
+{
+    /* RTC on STM32F0 is online even on sleep modes. No need to power on. */
+}
+
+void rtc_poweroff(void)
+{
+    /* Enable write access to RTC registers */
+    RCC->APB1ENR |= RCC_APB1ENR_PWREN;
+    PWR->CR |= PWR_CR_DBP;
+
+    /* Reset RTC domain */
+    RCC->BDCR |= RCC_BDCR_BDRST;
+    RCC->BDCR &= ~(RCC_BDCR_BDRST);
+    /* Disable the RTC */
+    RCC->BDCR &= ~RCC_BDCR_RTCEN;
+    /* Disable LSE clock */
+    RCC->BDCR &= ~(RCC_BDCR_LSEON);
+}
+
+void isr_rtc(void)
+{
+
+    if ((RTC->ISR & RTC_ISR_ALRAF) && (rtc_callback.cb != NULL)) {
+        rtc_callback.cb(rtc_callback.arg);
+        RTC->ISR &= ~RTC_ISR_ALRAF;
+    }
+    if (sched_context_switch_request) {
+        thread_yield();
+    }
+}
+
+/**
+ * Convert a number from unsigned to BCD
+ *
+ * @param[in] value to be converted
+ * @return BCD representation of the value
+ */
+static uint8_t byte2bcd(uint8_t value)
+{
+  uint8_t bcdhigh = 0;
+
+  while (value >= 10)
+  {
+    bcdhigh++;
+    value -= 10;
+  }
+
+  return  ((uint8_t)(bcdhigh << 4) | value);
+}
+
+#endif /* RTC_NUMOF */

tests/periph_rtc/Makefile

+export APPLICATION = periph_rtc
+include ../Makefile.tests_common
+
+FEATURES_REQUIRED = periph_rtc
+
+DISABLE_MODULE += auto_init
+
+include $(RIOTBASE)/Makefile.include

tests/periph_rtc/README.md

+Expected result
+===============
+When everything works as expected, you should see a alarm message after 10 seconds from start-up.
+
+Background
+==========
+Test for the low-level RTC driver.

tests/periph_rtc/main.c

+/*
+ * Copyright (C) 2015 Lari Lehtomäki
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @ingroup tests
+ * @{
+ *
+ * @file
+ * @brief       Test for low-level Real Time clock drivers
+ *
+ * This test will initialize the real-time timer and trigger an alarm printing
+ * 'Hello' every 10 seconds
+ *
+ * @author      Lari Lehtomäki <lari@lehtomaki.fi>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <time.h>
+
+#include "periph_conf.h"
+#include "periph/rtc.h"
+#include "hwtimer.h"
+
+#define TM_YEAR_OFFSET              (1900)
+
+#if RTC_NUMOF < 1
+#error "No RTC found. See the board specific periph_conf.h."
+#endif
+
+void cb(void *arg)
+{
+    (void)arg;
+
+    puts("Alarm!");
+
+    struct tm time;
+    rtc_get_alarm(&time);
+    time.tm_sec  += 10;
+    if ( time.tm_sec > 60 )
+        rtc_clear_alarm();
+    rtc_set_alarm(&time, cb, 0);
+}
+
+
+int main(void)
+{
+    puts("\nRIOT RTC low-level driver test");
+    puts("This test will display 'Alarm' in 10 seconds\n");
+
+    puts("Initializing the RTC driver");
+    rtc_init();
+
+    struct tm time;
+    time.tm_year = 2011 - TM_YEAR_OFFSET; // years are counted from 1900
+    time.tm_mon  = 11; // 0 = January, 11 = December
+    time.tm_mday = 13;
+    time.tm_hour = 14;
+    time.tm_min  = 15;
+    time.tm_sec  = 15;
+
+    printf("Setting clock to %04d-%02d-%02d %02d:%02d:%02d\n",
+                                                    time.tm_year + TM_YEAR_OFFSET,
+                                                    time.tm_mon + 1,
+                                                    time.tm_mday,
+                                                    time.tm_hour,
+                                                    time.tm_min,
+                                                    time.tm_sec);
+    rtc_set_time(&time);
+
+    hwtimer_wait(100);
+
+    rtc_get_time(&time);
+    printf("Clock set to %04d-%02d-%02d %02d:%02d:%02d\n",
+                                                    time.tm_year + TM_YEAR_OFFSET,
+                                                    time.tm_mon + 1,
+                                                    time.tm_mday,
+                                                    time.tm_hour,
+                                                    time.tm_min,
+                                                    time.tm_sec);
+
+
+    time.tm_sec  += 10;
+
+    printf("Setting alarm to %04d-%02d-%02d %02d:%02d:%02d\n",
+                                                    time.tm_year + TM_YEAR_OFFSET,
+                                                    time.tm_mon + 1,
+                                                    time.tm_mday,
+                                                    time.tm_hour,
+                                                    time.tm_min,
+                                                    time.tm_sec);
+    rtc_set_alarm(&time, cb, 0);
+
+    hwtimer_wait(100);
+
+    rtc_get_alarm(&time);
+    printf("Alarm set to %04d-%02d-%02d %02d:%02d:%02d\n",
+                                                    time.tm_year + TM_YEAR_OFFSET,
+                                                    time.tm_mon + 1,
+                                                    time.tm_mday,
+                                                    time.tm_hour,
+                                                    time.tm_min,
+                                                    time.tm_sec);
+
+    puts("The alarm should trigger every 10 seconds for 4 times.");
+    return 0;
+}