feat: support nrf54 GRTC as time-driver

* Refactor GRTC peripheral splitting it into multiple channels
* Reserve channel 1 for time-driver if enabled
* Implement time-driver using GRTC (RTC peripheral is now removed).
* Add timer example to nrf54l15

4 files changed, 147 insertions, 57 deletions

diff --git a/embassy-nrf/Cargo.toml b/embassy-nrf/Cargo.toml
index 08f4b280b..0a71094eb 100644
--- a/embassy-nrf/Cargo.toml
+++ b/embassy-nrf/Cargo.toml
@@ -23,8 +23,8 @@ build = [
     {target = "thumbv8m.main-none-eabihf", features = ["gpiote", "nrf5340-app-s", "time", "time-driver-rtc1"]},
     {target = "thumbv8m.main-none-eabihf", features = ["gpiote", "nrf5340-app-ns", "time", "time-driver-rtc1"]},
     {target = "thumbv8m.main-none-eabihf", features = ["gpiote", "nrf5340-net", "time", "time-driver-rtc1"]},
-    {target = "thumbv8m.main-none-eabihf", features = ["gpiote", "nrf54l15-app-s", "time", "time-driver-rtc1"]},
-    {target = "thumbv8m.main-none-eabihf", features = ["gpiote", "nrf54l15-app-ns", "time", "time-driver-rtc1"]},
+    {target = "thumbv8m.main-none-eabihf", features = ["gpiote", "nrf54l15-app-s", "time", "time-driver-grtc"]},
+    {target = "thumbv8m.main-none-eabihf", features = ["gpiote", "nrf54l15-app-ns", "time", "time-driver-grtc"]},
     {target = "thumbv7em-none-eabi", features = ["gpiote", "nrf52840", "time"]},
     {target = "thumbv7em-none-eabi", features = ["gpiote", "nrf52840", "time-driver-rtc1"]},
     {target = "thumbv7em-none-eabi", features = ["gpiote", "nrf52840", "time", "time-driver-rtc1"]},
@@ -80,9 +80,10 @@ unstable-pac = []
 gpiote = []
 
 ## Use RTC1 as the time driver for `embassy-time`, with a tick rate of 32.768khz
-## 
-## Note: For nRF54L, it's actually RTC30
-time-driver-rtc1 = ["_time-driver"]
+time-driver-rtc1 = ["_time-driver", "embassy-time-driver?/tick-hz-32_768"]
+
+## Use GRTC (CC n=1, GRTC_1 irq) as the time driver for `embassy-time`, with a tick rate of 1 MHz
+time-driver-grtc = ["_time-driver", "embassy-time-driver?/tick-hz-1_000_000"]
 
 ## Enable embassy-net 802.15.4 driver
 net-driver = ["_net-driver"]
@@ -152,7 +153,7 @@ _nrf5340-net = ["_nrf5340", "nrf-pac/nrf5340-net"]
 _nrf5340 = ["_gpio-p1", "_dppi"]
 _nrf54l15-app = ["_nrf54l15", "nrf-pac/nrf54l15-app"]
 _nrf54l15 = ["_nrf54l", "_gpio-p1", "_gpio-p2"]
-_nrf54l = ["_dppi"]
+_nrf54l = ["_dppi", "_grtc"]
 
 _nrf9160 = ["nrf-pac/nrf9160", "_dppi", "_spi-v1"]
 _nrf9120 = ["nrf-pac/nrf9120", "_dppi", "_spi-v1"]
@@ -160,7 +161,7 @@ _nrf52 = ["_ppi"]
 _nrf51 = ["_ppi", "_spi-v1"]
 _nrf91 = []
 
-_time-driver = ["dep:embassy-time-driver", "embassy-time-driver?/tick-hz-32_768", "dep:embassy-time-queue-utils", "embassy-embedded-hal/time"]
+_time-driver = ["dep:embassy-time-driver", "dep:embassy-time-queue-utils", "embassy-embedded-hal/time"]
 
 _net-driver = ["dep:embassy-net-driver-channel","dep:embassy-futures"]
 
@@ -173,6 +174,7 @@ _dppi = []
 _gpio-p1 = []
 _gpio-p2 = []
 _spi-v1 = []
+_grtc = []
 
 # Errata workarounds
 _nrf52832_anomaly_109 = []
@@ -200,7 +202,7 @@ embedded-io-async = { version = "0.6.1" }
 rand-core-06 = { package = "rand_core", version = "0.6" }
 rand-core-09 = { package = "rand_core", version = "0.9" }
 
-nrf-pac = { version = "0.1.0", git = "https://github.com/embassy-rs/nrf-pac.git", rev = "58198c23bce72edc10b4e1656d1b54441fc74e7c" }
+nrf-pac = { version = "0.1.0", git = "https://github.com/embassy-rs/nrf-pac.git", rev = "0068816c482932e3c59964817610ef41e79a6843" }
 
 defmt = { version = "1.0.1", optional = true }
 bitflags = "2.4.2"
diff --git a/embassy-nrf/src/chips/nrf54l15_app.rs b/embassy-nrf/src/chips/nrf54l15_app.rs
index 8846717db..b6c9fd110 100644
--- a/embassy-nrf/src/chips/nrf54l15_app.rs
+++ b/embassy-nrf/src/chips/nrf54l15_app.rs
@@ -26,7 +26,6 @@ pub mod pac {
         PPIB10_NS as PPIB10,
         PPIB11_NS as PPIB11,
         TIMER10_NS as TIMER10,
-        RTC10_NS as RTC10,
         EGU10_NS as EGU10,
         RADIO_NS as RADIO,
         DPPIC20_NS as DPPIC20,
@@ -76,7 +75,6 @@ pub mod pac {
         TWIM30_NS as TWIM30,
         TWIS30_NS as TWIS30,
         UARTE30_NS as UARTE30,
-        RTC30_NS as RTC30,
         COMP_NS as COMP,
         LPCOMP_NS as LPCOMP,
         WDT31_NS as WDT31,
@@ -127,7 +125,6 @@ pub mod pac {
         PPIB10_S as PPIB10,
         PPIB11_S as PPIB11,
         TIMER10_S as TIMER10,
-        RTC10_S as RTC10,
         EGU10_S as EGU10,
         RADIO_S as RADIO,
         SPU20_S as SPU20,
@@ -180,7 +177,6 @@ pub mod pac {
         TWIM30_S as TWIM30,
         TWIS30_S as TWIS30,
         UARTE30_S as UARTE30,
-        RTC30_S as RTC30,
         COMP_S as COMP,
         LPCOMP_S as LPCOMP,
         WDT30_S as WDT30,
@@ -417,11 +413,19 @@ embassy_hal_internal::peripherals! {
     P2_10,
 
     // GRTC
-    GRTC,
-
-    // RTC
-    RTC10,
-    RTC30,
+    GRTC_CH0,
+    #[cfg(not(feature = "time-driver-grtc"))]
+    GRTC_CH1,
+    GRTC_CH2,
+    GRTC_CH3,
+    GRTC_CH4,
+    GRTC_CH5,
+    GRTC_CH6,
+    GRTC_CH7,
+    GRTC_CH8,
+    GRTC_CH9,
+    GRTC_CH10,
+    GRTC_CH11,
 
     // PWM
     PWM20,
@@ -548,9 +552,6 @@ cfg_if::cfg_if! {
     }
 }
 
-impl_rtc!(RTC10, RTC10, RTC10);
-impl_rtc!(RTC30, RTC30, RTC30);
-
 #[cfg(feature = "_ns")]
 impl_wdt!(WDT, WDT31, WDT31, 0);
 #[cfg(feature = "_s")]
@@ -703,7 +704,6 @@ embassy_hal_internal::interrupt_mod!(
     TIMER00,
     SPU10,
     TIMER10,
-    RTC10,
     EGU10,
     RADIO_0,
     RADIO_1,
@@ -737,11 +737,9 @@ embassy_hal_internal::interrupt_mod!(
     GRTC_3,
     SPU30,
     SERIAL30,
-    RTC30,
     COMP_LPCOMP,
     WDT30,
     WDT31,
     GPIOTE30_0,
     GPIOTE30_1,
-    CLOCK_POWER,
 );
diff --git a/embassy-nrf/src/lib.rs b/embassy-nrf/src/lib.rs
index 28d2119ae..e8762b00d 100644
--- a/embassy-nrf/src/lib.rs
+++ b/embassy-nrf/src/lib.rs
@@ -153,6 +153,7 @@ pub mod reset;
 #[cfg(not(feature = "_nrf54l"))]
 #[cfg(not(any(feature = "_nrf5340-app", feature = "_nrf91")))]
 pub mod rng;
+#[cfg(not(feature = "_nrf54l"))]
 pub mod rtc;
 #[cfg(not(any(feature = "_nrf51", feature = "nrf52820", feature = "_nrf5340-net")))]
 pub mod saadc;
diff --git a/embassy-nrf/src/time_driver.rs b/embassy-nrf/src/time_driver.rs
index b723e2334..de1974fb7 100644
--- a/embassy-nrf/src/time_driver.rs
+++ b/embassy-nrf/src/time_driver.rs
@@ -1,4 +1,5 @@
 use core::cell::{Cell, RefCell};
+#[cfg(not(feature = "_grtc"))]
 use core::sync::atomic::{AtomicU32, Ordering, compiler_fence};
 
 use critical_section::CriticalSection;
@@ -8,21 +9,27 @@ use embassy_time_driver::Driver;
 use embassy_time_queue_utils::Queue;
 
 use crate::interrupt::InterruptExt;
+#[cfg(feature = "_grtc")]
+use crate::pac::grtc::vals::Busy;
 use crate::{interrupt, pac};
 
-#[cfg(feature = "_nrf54l")]
-fn rtc() -> pac::rtc::Rtc {
-    pac::RTC30
+#[cfg(feature = "_grtc")]
+fn rtc() -> pac::grtc::Grtc {
+    pac::GRTC
 }
-#[cfg(not(feature = "_nrf54l"))]
+
+#[cfg(not(feature = "_grtc"))]
 fn rtc() -> pac::rtc::Rtc {
     pac::RTC1
 }
 
 /// Calculate the timestamp from the period count and the tick count.
 ///
-/// The RTC counter is 24 bit. Ticking at 32768hz, it overflows every ~8 minutes. This is
-/// too short. We must make it "never" overflow.
+/// For nRF54 devices and newer, the GRTC counter is 52 bits, so the time driver uses the
+/// syscounter and ignores the periods handling, since it overflows every 142 years.
+///
+/// For most other devices, the RTC counter is 24 bit. Ticking at 32768hz, it overflows every ~8 minutes.
+/// This is too short. We must make it "never" overflow.
 ///
 /// The obvious way would be to count overflow periods. Every time the counter overflows,
 /// increase a `periods` variable. `now()` simply does `periods << 24 + counter`. So, the logic
@@ -64,14 +71,39 @@ fn rtc() -> pac::rtc::Rtc {
 /// `period` is a 32bit integer, so It overflows on 2^32 * 2^23 / 32768 seconds of uptime, which is 34865
 /// years. For comparison, flash memory like the one containing your firmware is usually rated to retain
 /// data for only 10-20 years. 34865 years is long enough!
+#[cfg(not(feature = "_grtc"))]
 fn calc_now(period: u32, counter: u32) -> u64 {
     ((period as u64) << 23) + ((counter ^ ((period & 1) << 23)) as u64)
 }
 
+#[cfg(feature = "_grtc")]
+fn syscounter() -> u64 {
+    let r = rtc();
+    r.syscounter(0).active().write(|w| w.set_active(true));
+    loop {
+        let countl: u32 = r.syscounter(0).syscounterl().read();
+        let counth = r.syscounter(0).syscounterh().read();
+
+        if counth.busy() == Busy::READY && !counth.overflow() {
+            let counth: u32 = counth.value();
+            let count = countl as u64 | ((counth as u64) << 32);
+            r.syscounter(0).active().write(|w| w.set_active(false));
+            return count;
+        }
+        // If overflow or not ready, loop will re-read both registers
+    }
+}
+
+#[cfg(not(feature = "_grtc"))]
 fn compare_n(n: usize) -> u32 {
     1 << (n + 16)
 }
 
+#[cfg(feature = "_grtc")]
+fn compare_n(n: usize) -> u32 {
+    1 << n // GRTC uses bits 0-11 for COMPARE[0-11]
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -108,6 +140,7 @@ impl AlarmState {
 
 struct RtcDriver {
     /// Number of 2^23 periods elapsed since boot.
+    #[cfg(not(feature = "_grtc"))]
     period: AtomicU32,
     /// Timestamp at which to fire alarm. u64::MAX if no alarm is scheduled.
     alarms: Mutex<AlarmState>,
@@ -115,6 +148,7 @@ struct RtcDriver {
 }
 
 embassy_time_driver::time_driver_impl!(static DRIVER: RtcDriver = RtcDriver {
+    #[cfg(not(feature = "_grtc"))]
     period: AtomicU32::new(0),
     alarms: Mutex::const_new(CriticalSectionRawMutex::new(), AlarmState::new()),
     queue: Mutex::new(RefCell::new(Queue::new())),
@@ -123,25 +157,48 @@ embassy_time_driver::time_driver_impl!(static DRIVER: RtcDriver = RtcDriver {
 impl RtcDriver {
     fn init(&'static self, irq_prio: crate::interrupt::Priority) {
         let r = rtc();
-        r.cc(3).write(|w| w.set_compare(0x800000));
+        // Chips without GRTC needs to deal with overflow
+        #[cfg(not(feature = "_grtc"))]
+        {
+            r.cc(3).write(|w| w.set_compare(0x800000));
 
-        r.intenset().write(|w| {
-            w.set_ovrflw(true);
-            w.set_compare(3, true);
-        });
+            r.intenset().write(|w| {
+                w.set_ovrflw(true);
+                w.set_compare(3, true);
+            });
+        }
 
+        #[cfg(feature = "_grtc")]
+        {
+            r.mode().write(|w| {
+                w.set_syscounteren(true);
+            });
+        }
         r.tasks_clear().write_value(1);
         r.tasks_start().write_value(1);
 
         // Wait for clear
+        #[cfg(not(feature = "_grtc"))]
         while r.counter().read().0 != 0 {}
 
-        #[cfg(feature = "_nrf54l")]
+        #[cfg(feature = "_grtc")]
+        {
+            // According to datasheet, we need to wait for STATUS.LFTIMER.READY
+            // before the timer is actually started
+            loop {
+                if r.status().lftimer().read().ready() {
+                    break;
+                }
+            }
+            // Keep SYSCOUNTER[0] always active so we can read it anytime without BUSY waits
+        }
+
+        #[cfg(feature = "_grtc")]
         {
-            interrupt::RTC30.set_priority(irq_prio);
-            unsafe { interrupt::RTC30.enable() };
+            interrupt::GRTC_1.set_priority(irq_prio);
+            unsafe { interrupt::GRTC_1.enable() };
         }
-        #[cfg(not(feature = "_nrf54l"))]
+        #[cfg(not(feature = "_grtc"))]
         {
             interrupt::RTC1.set_priority(irq_prio);
             unsafe { interrupt::RTC1.enable() };
@@ -150,11 +207,14 @@ impl RtcDriver {
 
     fn on_interrupt(&self) {
         let r = rtc();
+
+        #[cfg(not(feature = "_grtc"))]
         if r.events_ovrflw().read() == 1 {
             r.events_ovrflw().write_value(0);
             self.next_period();
         }
 
+        #[cfg(not(feature = "_grtc"))]
         if r.events_compare(3).read() == 1 {
             r.events_compare(3).write_value(0);
             self.next_period();
@@ -169,6 +229,7 @@ impl RtcDriver {
         }
     }
 
+    #[cfg(not(feature = "_grtc"))]
     fn next_period(&self) {
         critical_section::with(|cs| {
             let r = rtc();
@@ -190,7 +251,10 @@ impl RtcDriver {
     fn trigger_alarm(&self, cs: CriticalSection) {
         let n = 0;
         let r = rtc();
+        #[cfg(not(feature = "_grtc"))]
         r.intenclr().write(|w| w.0 = compare_n(n));
+        #[cfg(feature = "_grtc")]
+        r.intenclr(1).write(|w| w.0 = compare_n(n));
 
         let alarm = &self.alarms.borrow(cs);
         alarm.timestamp.set(u64::MAX);
@@ -214,7 +278,10 @@ impl RtcDriver {
             if timestamp <= t {
                 // If alarm timestamp has passed the alarm will not fire.
                 // Disarm the alarm and return `false` to indicate that.
+                #[cfg(not(feature = "_grtc"))]
                 r.intenclr().write(|w| w.0 = compare_n(n));
+                #[cfg(feature = "_grtc")]
+                r.intenclr(1).write(|w| w.0 = compare_n(n));
 
                 alarm.timestamp.set(u64::MAX);
 
@@ -226,7 +293,7 @@ impl RtcDriver {
             // Write the CC value regardless of whether we're going to enable it now or not.
             // This way, when we enable it later, the right value is already set.
 
-            // nrf52 docs say:
+            // nrf52 docs say :
             //    If the COUNTER is N, writing N or N+1 to a CC register may not trigger a COMPARE event.
             // To workaround this, we never write a timestamp smaller than N+3.
             // N+2 is not safe because rtc can tick from N to N+1 between calling now() and writing cc.
@@ -238,22 +305,39 @@ impl RtcDriver {
             // This means that an alarm can be delayed for up to 2 ticks (from t+1 to t+3), but this is allowed
             // by the Alarm trait contract. What's not allowed is triggering alarms *before* their scheduled time,
             // and we don't do that here.
-            let safe_timestamp = timestamp.max(t + 3);
-            r.cc(n).write(|w| w.set_compare(safe_timestamp as u32 & 0xFFFFFF));
-
-            let diff = timestamp - t;
-            if diff < 0xc00000 {
-                r.intenset().write(|w| w.0 = compare_n(n));
-
-                // If we have not passed the timestamp, we can be sure the alarm will be invoked. Otherwise,
-                // we need to retry setting the alarm.
-                if self.now() + 2 <= timestamp {
+            #[cfg(not(feature = "_grtc"))]
+            {
+                let safe_timestamp = timestamp.max(t + 3);
+                r.cc(n).write(|w| w.set_compare(safe_timestamp as u32 & 0xFFFFFF));
+                let diff = timestamp - t;
+                if diff < 0xc00000 {
+                    r.intenset().write(|w| w.0 = compare_n(n));
+
+                    // If we have not passed the timestamp, we can be sure the alarm will be invoked. Otherwise,
+                    // we need to retry setting the alarm.
+                    if self.now() + 2 <= timestamp {
+                        return true;
+                    }
+                } else {
+                    // If it's too far in the future, don't setup the compare channel yet.
+                    // It will be setup later by `next_period`.
+                    r.intenclr().write(|w| w.0 = compare_n(n));
                     return true;
                 }
-            } else {
-                // If it's too far in the future, don't setup the compare channel yet.
-                // It will be setup later by `next_period`.
-                r.intenclr().write(|w| w.0 = compare_n(n));
+            }
+
+            // The nRF54 datasheet states that 'The EVENTS_COMPARE[n] event is generated immediately if the
+            // configured compare value at CC[n] is less than the current SYSCOUNTER value.'. This means we
+            // can write the expected timestamp and be sure the alarm is triggered.
+            #[cfg(feature = "_grtc")]
+            {
+                let ccl = timestamp as u32;
+                let cch = (timestamp >> 32) as u32 & 0xFFFFF; // 20 bits for CCH
+
+                r.cc(n).ccl().write_value(ccl);
+                r.cc(n).cch().write(|w| w.set_cch(cch));
+                r.intenset(1).write(|w| w.0 = compare_n(n));
+
                 return true;
             }
         }
@@ -261,6 +345,7 @@ impl RtcDriver {
 }
 
 impl Driver for RtcDriver {
+    #[cfg(not(feature = "_grtc"))]
     fn now(&self) -> u64 {
         // `period` MUST be read before `counter`, see comment at the top for details.
         let period = self.period.load(Ordering::Relaxed);
@@ -269,10 +354,14 @@ impl Driver for RtcDriver {
         calc_now(period, counter)
     }
 
+    #[cfg(feature = "_grtc")]
+    fn now(&self) -> u64 {
+        syscounter()
+    }
+
     fn schedule_wake(&self, at: u64, waker: &core::task::Waker) {
         critical_section::with(|cs| {
             let mut queue = self.queue.borrow(cs).borrow_mut();
-
             if queue.schedule_wake(at, waker) {
                 let mut next = queue.next_expiration(self.now());
                 while !self.set_alarm(cs, next) {
@@ -283,14 +372,14 @@ impl Driver for RtcDriver {
     }
 }
 
-#[cfg(feature = "_nrf54l")]
+#[cfg(feature = "_grtc")]
 #[cfg(feature = "rt")]
 #[interrupt]
-fn RTC30() {
+fn GRTC_1() {
     DRIVER.on_interrupt()
 }
 
-#[cfg(not(feature = "_nrf54l"))]
+#[cfg(not(feature = "_grtc"))]
 #[cfg(feature = "rt")]
 #[interrupt]
 fn RTC1() {