From 7c1b5630d2a77904a450c21a943de2a3a1135cd1 Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benpicco@googlemail.com>
Date: Tue, 4 May 2021 17:27:20 +0200
Subject: [PATCH] cpu/atmega_common: RTC: implement rtc_get_time_ms()

---
 cpu/atmega_common/Kconfig           |  1 +
 cpu/atmega_common/Makefile.features |  1 +
 cpu/atmega_common/periph/rtc.c      | 22 ++++++++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/cpu/atmega_common/Kconfig b/cpu/atmega_common/Kconfig
index 599b319719..0e1079c5dd 100644
--- a/cpu/atmega_common/Kconfig
+++ b/cpu/atmega_common/Kconfig
@@ -20,6 +20,7 @@ config CPU_COMMON_ATMEGA
     select HAS_PERIPH_GPIO
     select HAS_PERIPH_GPIO_IRQ
     select HAS_PERIPH_PM
+    select HAS_PERIPH_RTC_MS
     select HAS_PERIPH_RTT_SET_COUNTER
     select HAS_PERIPH_TIMER_PERIODIC
     select HAS_PERIPH_WDT
diff --git a/cpu/atmega_common/Makefile.features b/cpu/atmega_common/Makefile.features
index 7b58b012bd..12dc75ff88 100644
--- a/cpu/atmega_common/Makefile.features
+++ b/cpu/atmega_common/Makefile.features
@@ -10,6 +10,7 @@ FEATURES_PROVIDED += periph_cpuid
 FEATURES_PROVIDED += periph_eeprom
 FEATURES_PROVIDED += periph_gpio periph_gpio_irq
 FEATURES_PROVIDED += periph_pm
+FEATURES_PROVIDED += periph_rtc_ms
 FEATURES_PROVIDED += periph_rtt_set_counter
 FEATURES_PROVIDED += periph_timer_periodic
 FEATURES_PROVIDED += periph_wdt
diff --git a/cpu/atmega_common/periph/rtc.c b/cpu/atmega_common/periph/rtc.c
index 08ad449461..ea80deb851 100644
--- a/cpu/atmega_common/periph/rtc.c
+++ b/cpu/atmega_common/periph/rtc.c
@@ -102,6 +102,28 @@ int rtc_get_time(struct tm *time)
     return 0;
 }
 
+int rtc_get_time_ms(struct tm *time, uint16_t *ms)
+{
+    uint8_t cnt_before, cnt_after;
+
+    /* loop in case of overflow */
+    do {
+        cnt_before = TCNT2;
+
+        /* prevent compiler from reordering memory access to tm_now,
+         * including moving it out of the loop
+         */
+        __asm__ volatile ("" : : : "memory");
+        *time = tm_now;
+
+        cnt_after  = TCNT2;
+    } while (cnt_before > cnt_after);
+
+    *ms = (cnt_after * 1000UL) >> 8;
+
+    return 0;
+}
+
 int rtc_get_alarm(struct tm *time)
 {
     *time = tm_alarm;