Enable RTC on STM32WL chips (#1645)

* Add clippy allow to not report if same then branch

* Support enabling RTC clock on STM32WL

* Add clippy allow to not report if same then branch

* Support enabling RTC clock on STM32WL

* Add rtc example for stm32wl

* Address code review feedback

5 files changed, 108 insertions, 4 deletions

diff --git a/embassy-stm32/src/rcc/wl.rs b/embassy-stm32/src/rcc/wl.rs
index 7072db984..6b69bb1cb 100644
--- a/embassy-stm32/src/rcc/wl.rs
+++ b/embassy-stm32/src/rcc/wl.rs
@@ -1,4 +1,5 @@
-use crate::pac::{FLASH, RCC};
+use crate::pac::pwr::vals::Dbp;
+use crate::pac::{FLASH, PWR, RCC};
 use crate::rcc::{set_freqs, Clocks};
 use crate::time::Hertz;
 
@@ -184,6 +185,8 @@ pub struct Config {
     pub apb1_pre: APBPrescaler,
     pub apb2_pre: APBPrescaler,
     pub enable_lsi: bool,
+    pub enable_rtc_apb: bool,
+    pub rtc_mux: RtcClockSource,
 }
 
 impl Default for Config {
@@ -196,10 +199,25 @@ impl Default for Config {
             apb1_pre: APBPrescaler::NotDivided,
             apb2_pre: APBPrescaler::NotDivided,
             enable_lsi: false,
+            enable_rtc_apb: false,
+            rtc_mux: RtcClockSource::LSI32,
         }
     }
 }
 
+pub enum RtcClockSource {
+    LSE32,
+    LSI32,
+}
+
+#[repr(u8)]
+pub enum Lsedrv {
+    Low = 0,
+    MediumLow = 1,
+    MediumHigh = 2,
+    High = 3,
+}
+
 pub(crate) unsafe fn init(config: Config) {
     let (sys_clk, sw, vos) = match config.mux {
         ClockSrc::HSI16 => (HSI_FREQ.0, 0x01, VoltageScale::Range2),
@@ -266,6 +284,32 @@ pub(crate) unsafe fn init(config: Config) {
 
     while FLASH.acr().read().latency() != ws {}
 
+    match config.rtc_mux {
+        RtcClockSource::LSE32 => {
+            // 1. Unlock the backup domain
+            PWR.cr1().modify(|w| w.set_dbp(Dbp::ENABLED));
+
+            // 2. Setup the LSE
+            RCC.bdcr().modify(|w| {
+                // Enable LSE
+                w.set_lseon(true);
+                // Max drive strength
+                // TODO: should probably be settable
+                w.set_lsedrv(Lsedrv::High as u8); //---// PAM - should not be commented
+            });
+
+            // Wait until LSE is running
+            while !RCC.bdcr().read().lserdy() {}
+        }
+        RtcClockSource::LSI32 => {
+            // Turn on the internal 32 kHz LSI oscillator
+            RCC.csr().modify(|w| w.set_lsion(true));
+
+            // Wait until LSI is running
+            while !RCC.csr().read().lsirdy() {}
+        }
+    }
+
     match config.mux {
         ClockSrc::HSI16 => {
             // Enable HSI16
@@ -287,11 +331,26 @@ pub(crate) unsafe fn init(config: Config) {
                 w.set_msirgsel(true);
                 w.set_msirange(range.into());
                 w.set_msion(true);
+
+                if let RtcClockSource::LSE32 = config.rtc_mux {
+                    // If LSE is enabled, enable calibration of MSI
+                    w.set_msipllen(true);
+                } else {
+                    w.set_msipllen(false);
+                }
             });
             while !RCC.cr().read().msirdy() {}
         }
     }
 
+    if config.enable_rtc_apb {
+        // enable peripheral clock for communication
+        crate::pac::RCC.apb1enr1().modify(|w| w.set_rtcapben(true));
+
+        // read to allow the pwr clock to enable
+        crate::pac::PWR.cr1().read();
+    }
+
     RCC.extcfgr().modify(|w| {
         if config.shd_ahb_pre == AHBPrescaler::NotDivided {
             w.set_shdhpre(0);
diff --git a/embassy-stm32/src/rtc/v3.rs b/embassy-stm32/src/rtc/v3.rs
index 7e5c64d90..8ef0ec51d 100644
--- a/embassy-stm32/src/rtc/v3.rs
+++ b/embassy-stm32/src/rtc/v3.rs
@@ -172,6 +172,7 @@ impl sealed::Instance for crate::peripherals::RTC {
     const BACKUP_REGISTER_COUNT: usize = 32;
 
     fn read_backup_register(_rtc: &Rtc, register: usize) -> Option<u32> {
+        #[allow(clippy::if_same_then_else)]
         if register < Self::BACKUP_REGISTER_COUNT {
             //Some(rtc.bkpr()[register].read().bits())
             None // RTC3 backup registers come from the TAMP peripe=heral, not RTC. Not() even in the L412 PAC
diff --git a/examples/stm32wl/.cargo/config.toml b/examples/stm32wl/.cargo/config.toml
index 4f8094ff2..ee416fcbc 100644
--- a/examples/stm32wl/.cargo/config.toml
+++ b/examples/stm32wl/.cargo/config.toml
@@ -3,7 +3,7 @@
 runner = "probe-rs run --chip STM32WLE5JCIx"
 
 [build]
-target = "thumbv7em-none-eabihf"
+target = "thumbv7em-none-eabi"
 
 [env]
 DEFMT_LOG = "trace"
diff --git a/examples/stm32wl/Cargo.toml b/examples/stm32wl/Cargo.toml
index 99f68387f..e2c66f456 100644
--- a/examples/stm32wl/Cargo.toml
+++ b/examples/stm32wl/Cargo.toml
@@ -8,8 +8,8 @@ license = "MIT OR Apache-2.0"
 embassy-sync = { version = "0.2.0", path = "../../embassy-sync", features = ["defmt"] }
 embassy-executor = { version = "0.2.0", path = "../../embassy-executor", features = ["nightly", "arch-cortex-m", "executor-thread", "defmt", "integrated-timers"] }
 embassy-time = { version = "0.1.2", path = "../../embassy-time", features = ["nightly", "unstable-traits", "defmt", "defmt-timestamp-uptime", "tick-hz-32_768"] }
-embassy-stm32 = { version = "0.1.0", path = "../../embassy-stm32", features = ["nightly", "unstable-traits", "defmt", "stm32wl55jc-cm4", "time-driver-any", "memory-x", "unstable-pac", "exti"]  }
-embassy-embedded-hal = {version = "0.1.0", path = "../../embassy-embedded-hal" }
+embassy-stm32 = { version = "0.1.0", path = "../../embassy-stm32", features = ["nightly", "unstable-traits", "defmt", "stm32wl55jc-cm4", "time-driver-any", "memory-x", "unstable-pac", "exti", "chrono"] }
+embassy-embedded-hal = { version = "0.1.0", path = "../../embassy-embedded-hal" }
 embassy-lora = { version = "0.1.0", path = "../../embassy-lora", features = ["stm32wl", "time", "defmt"] }
 lora-phy = { version = "1" }
 lorawan-device = { version = "0.10.0", default-features = false, features = ["async", "external-lora-phy"] }
@@ -25,6 +25,7 @@ embedded-storage = "0.3.0"
 panic-probe = { version = "0.3", features = ["print-defmt"] }
 futures = { version = "0.3.17", default-features = false, features = ["async-await"] }
 heapless = { version = "0.7.5", default-features = false }
+chrono = { version = "^0.4", default-features = false }
 
 [patch.crates-io]
 lora-phy = { git = "https://github.com/embassy-rs/lora-phy", rev = "ad289428fd44b02788e2fa2116445cc8f640a265" }
diff --git a/examples/stm32wl/src/bin/rtc.rs b/examples/stm32wl/src/bin/rtc.rs
new file mode 100644
index 000000000..e11825499
--- /dev/null
+++ b/examples/stm32wl/src/bin/rtc.rs
@@ -0,0 +1,43 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use chrono::{NaiveDate, NaiveDateTime};
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_stm32::rcc::{self, ClockSrc};
+use embassy_stm32::rtc::{Rtc, RtcConfig};
+use embassy_stm32::Config;
+use embassy_time::{Duration, Timer};
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = {
+        let mut config = Config::default();
+        config.rcc.mux = ClockSrc::HSE32;
+        config.rcc.rtc_mux = rcc::RtcClockSource::LSE32;
+        config.rcc.enable_rtc_apb = true;
+        embassy_stm32::init(config)
+    };
+    info!("Hello World!");
+
+    let now = NaiveDate::from_ymd_opt(2020, 5, 15)
+        .unwrap()
+        .and_hms_opt(10, 30, 15)
+        .unwrap();
+
+    let mut rtc = Rtc::new(
+        p.RTC,
+        RtcConfig::default().clock_config(embassy_stm32::rtc::RtcClockSource::LSE),
+    );
+    info!("Got RTC! {:?}", now.timestamp());
+
+    rtc.set_datetime(now.into()).expect("datetime not set");
+
+    // In reality the delay would be much longer
+    Timer::after(Duration::from_millis(20000)).await;
+
+    let then: NaiveDateTime = rtc.now().unwrap().into();
+    info!("Got RTC! {:?}", then.timestamp());
+}