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// SPDX-FileCopyrightText: 2022 Foundation Devices, Inc. <hello@foundationdevices.com>

// SPDX-License-Identifier: Apache-2.0

use atsama5d27::trng::{Enabled, StatefulTrng, Trng};

use utralib::HW_TRNG_BASE;

use xous_kernel::{MemoryFlags, MemoryType, PID};

use crate::mem::MemoryManager;

/// The manually chosen virtual address has to be in the top 4MiB as it is the

/// only page shared among all processes.

///

/// See https://github.com/betrusted-io/xous-core/blob/master/docs/memory.md

pub const TRNG_KERNEL_ADDR: usize = 0xffce_0000;

pub static mut TRNG_KERNEL: Option<TrngKernel> = None;

pub struct TrngKernel {

base_addr: usize,

pub inner: Option<StatefulTrng<Enabled>>,

}

impl TrngKernel {

pub fn new(addr: usize) -> TrngKernel { TrngKernel { base_addr: addr, inner: None } }

pub fn init(&mut self) { self.inner = Some(Trng::with_alt_base_addr(self.base_addr as u32).enable()); }

pub fn get_u32(&mut self) -> u32 {

if let Some(trng) = &self.inner {

return trng.read_u32();

}

unreachable!()

}

}

/// Initialize TRNG driver.

///

/// Needed so that the kernel can allocate names.

///

/// # Panics

///

/// If \\`pmc::init()\\` hasn't called prior to calling this function.

pub fn init() {

// PMC driver should be initialized before.

super::pmc::enable_trng();

// Map the TRNG so that we can allocate names

// hardware guarantees that:

// - TRNG will automatically power on

// - Both TRNGs are enabled, with conservative defaults

// - Kernel FIFO will fill with TRNGs such that at least the next 512 calls to get_u32() will succeed

// without delay

// - The kernel will start a TRNG server

// - All further security decisions and policies are 100% delegated to this new server.

MemoryManager::with_mut(|memory_manager| {

memory_manager

.map_range(

HW_TRNG_BASE as *mut u8,

(TRNG_KERNEL_ADDR & !4095) as *mut u8,

0x4000, // 16K

PID::new(1).unwrap(),

MemoryFlags::R | MemoryFlags::W | MemoryFlags::DEV,

MemoryType::Default,

)

.expect("unable to map TRNG_KERNEL")

});

let mut trng_kernel = TrngKernel::new(TRNG_KERNEL_ADDR);

trng_kernel.init();

unsafe {

TRNG_KERNEL = Some(trng_kernel);

}

}

/// Retrieve random \\`u32\\`.

pub fn get_u32() -> u32 {

unsafe { TRNG_KERNEL.as_mut().expect("TRNG_KERNEL driver not initialized").get_u32() }

}