Add embassy-imxrt RNG driver

2 files changed, 258 insertions, 0 deletions

diff --git a/embassy-imxrt/src/lib.rs b/embassy-imxrt/src/lib.rs
index ad9f81e88..f728ba060 100644
--- a/embassy-imxrt/src/lib.rs
+++ b/embassy-imxrt/src/lib.rs
@@ -20,6 +20,7 @@ pub(crate) mod fmt;
 pub mod clocks;
 pub mod gpio;
 pub mod iopctl;
+pub mod rng;
 
 #[cfg(feature = "_time-driver")]
 pub mod time_driver;
diff --git a/embassy-imxrt/src/rng.rs b/embassy-imxrt/src/rng.rs
new file mode 100644
index 000000000..67e7ab65d
--- /dev/null
+++ b/embassy-imxrt/src/rng.rs
@@ -0,0 +1,257 @@
+//! True Random Number Generator (TRNG)
+
+use core::future::poll_fn;
+use core::marker::PhantomData;
+use core::task::Poll;
+
+use embassy_futures::block_on;
+use embassy_sync::waitqueue::AtomicWaker;
+use rand_core::{CryptoRng, RngCore};
+
+use crate::clocks::{enable_and_reset, SysconPeripheral};
+use crate::interrupt::typelevel::Interrupt;
+use crate::{interrupt, peripherals, Peri, PeripheralType};
+
+static RNG_WAKER: AtomicWaker = AtomicWaker::new();
+
+/// RNG ;error
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum Error {
+    /// Seed error.
+    SeedError,
+
+    /// HW Error.
+    HwError,
+
+    /// Frequency Count Fail
+    FreqCountFail,
+}
+
+/// RNG interrupt handler.
+pub struct InterruptHandler<T: Instance> {
+    _phantom: PhantomData<T>,
+}
+
+impl<T: Instance> interrupt::typelevel::Handler<T::Interrupt> for InterruptHandler<T> {
+    unsafe fn on_interrupt() {
+        let regs = T::info().regs;
+        let int_status = regs.int_status().read();
+
+        if int_status.ent_val().bit_is_set()
+            || int_status.hw_err().bit_is_set()
+            || int_status.frq_ct_fail().bit_is_set()
+        {
+            regs.int_ctrl().modify(|_, w| {
+                w.ent_val()
+                    .ent_val_0()
+                    .hw_err()
+                    .hw_err_0()
+                    .frq_ct_fail()
+                    .frq_ct_fail_0()
+            });
+            RNG_WAKER.wake();
+        }
+    }
+}
+
+/// RNG driver.
+pub struct Rng<'d> {
+    info: Info,
+    _lifetime: PhantomData<&'d ()>,
+}
+
+impl<'d> Rng<'d> {
+    /// Create a new RNG driver.
+    pub fn new<T: Instance>(
+        _inner: Peri<'d, T>,
+        _irq: impl interrupt::typelevel::Binding<T::Interrupt, InterruptHandler<T>> + 'd,
+    ) -> Self {
+        enable_and_reset::<T>();
+
+        let mut random = Self {
+            info: T::info(),
+            _lifetime: PhantomData,
+        };
+        random.init();
+
+        T::Interrupt::unpend();
+        unsafe { T::Interrupt::enable() };
+
+        random
+    }
+
+    /// Reset the RNG.
+    pub fn reset(&mut self) {
+        self.info.regs.mctl().write(|w| w.rst_def().set_bit().prgm().set_bit());
+    }
+
+    /// Fill the given slice with random values.
+    pub async fn async_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
+        // We have a total of 16 words (512 bits) of entropy at our
+        // disposal. The idea here is to read all bits and copy the
+        // necessary bytes to the slice.
+        for chunk in dest.chunks_mut(64) {
+            self.async_fill_chunk(chunk).await?;
+        }
+
+        Ok(())
+    }
+
+    async fn async_fill_chunk(&mut self, chunk: &mut [u8]) -> Result<(), Error> {
+        // wait for interrupt
+        let res = poll_fn(|cx| {
+            // Check if already ready.
+            // TODO: Is this necessary? Could we just check once after
+            // the waker has been registered?
+            if self.info.regs.int_status().read().ent_val().bit_is_set() {
+                return Poll::Ready(Ok(()));
+            }
+
+            RNG_WAKER.register(cx.waker());
+
+            self.unmask_interrupts();
+
+            let mctl = self.info.regs.mctl().read();
+
+            // Check again if interrupt fired
+            if mctl.ent_val().bit_is_set() {
+                Poll::Ready(Ok(()))
+            } else if mctl.err().bit_is_set() {
+                Poll::Ready(Err(Error::HwError))
+            } else if mctl.fct_fail().bit_is_set() {
+                Poll::Ready(Err(Error::FreqCountFail))
+            } else {
+                Poll::Pending
+            }
+        })
+        .await;
+
+        let bits = self.info.regs.mctl().read();
+
+        if bits.ent_val().bit_is_set() {
+            let mut entropy = [0; 16];
+
+            for (i, item) in entropy.iter_mut().enumerate() {
+                *item = self.info.regs.ent(i).read().bits();
+            }
+
+            // Read MCTL after reading ENT15
+            let _ = self.info.regs.mctl().read();
+
+            if entropy.iter().any(|e| *e == 0) {
+                return Err(Error::SeedError);
+            }
+
+            // SAFETY: entropy is the same for input and output types in
+            // native endianness.
+            let entropy: [u8; 64] = unsafe { core::mem::transmute(entropy) };
+
+            // write bytes to chunk
+            chunk.copy_from_slice(&entropy[..chunk.len()]);
+        }
+
+        res
+    }
+
+    fn mask_interrupts(&mut self) {
+        self.info.regs.int_mask().write(|w| {
+            w.ent_val()
+                .ent_val_0()
+                .hw_err()
+                .hw_err_0()
+                .frq_ct_fail()
+                .frq_ct_fail_0()
+        });
+    }
+
+    fn unmask_interrupts(&mut self) {
+        self.info.regs.int_mask().modify(|_, w| {
+            w.ent_val()
+                .ent_val_1()
+                .hw_err()
+                .hw_err_1()
+                .frq_ct_fail()
+                .frq_ct_fail_1()
+        });
+    }
+
+    fn enable_interrupts(&mut self) {
+        self.info.regs.int_ctrl().write(|w| {
+            w.ent_val()
+                .ent_val_1()
+                .hw_err()
+                .hw_err_1()
+                .frq_ct_fail()
+                .frq_ct_fail_1()
+        });
+    }
+
+    fn init(&mut self) {
+        self.mask_interrupts();
+
+        // Switch TRNG to programming mode
+        self.info.regs.mctl().modify(|_, w| w.prgm().set_bit());
+
+        self.enable_interrupts();
+
+        // Switch TRNG to Run Mode
+        self.info
+            .regs
+            .mctl()
+            .modify(|_, w| w.trng_acc().set_bit().prgm().clear_bit());
+    }
+}
+
+impl RngCore for Rng<'_> {
+    fn next_u32(&mut self) -> u32 {
+        let mut bytes = [0u8; 4];
+        block_on(self.async_fill_bytes(&mut bytes)).unwrap();
+        u32::from_ne_bytes(bytes)
+    }
+
+    fn next_u64(&mut self) -> u64 {
+        let mut bytes = [0u8; 8];
+        block_on(self.async_fill_bytes(&mut bytes)).unwrap();
+        u64::from_ne_bytes(bytes)
+    }
+
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        block_on(self.async_fill_bytes(dest)).unwrap();
+    }
+
+    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand_core::Error> {
+        self.fill_bytes(dest);
+        Ok(())
+    }
+}
+
+impl CryptoRng for Rng<'_> {}
+
+struct Info {
+    regs: crate::pac::Trng,
+}
+
+trait SealedInstance {
+    fn info() -> Info;
+}
+
+/// RNG instance trait.
+#[allow(private_bounds)]
+pub trait Instance: SealedInstance + PeripheralType + SysconPeripheral + 'static + Send {
+    /// Interrupt for this RNG instance.
+    type Interrupt: interrupt::typelevel::Interrupt;
+}
+
+impl Instance for peripherals::RNG {
+    type Interrupt = crate::interrupt::typelevel::RNG;
+}
+
+impl SealedInstance for peripherals::RNG {
+    fn info() -> Info {
+        // SAFETY: safe from single executor
+        Info {
+            regs: unsafe { crate::pac::Trng::steal() },
+        }
+    }
+}