trve/src/mem.rs

// Copyright (c) 2025 taitep
// SPDX-License-Identifier: MIT
//
// This file is part of TRVE (https://gitea.taitep.se/taitep/trve)
// See LICENSE file in the project root for full license text.

use std::sync::{
    Arc,
    atomic::{AtomicU8, AtomicU16, AtomicU32, AtomicU64, Ordering::Relaxed},
};

use memmap2::MmapMut;

use crate::{
    consts::{Byte, DWord, HWord, Word},
    exceptions::ExceptionType,
};

pub type PageNum = usize;

const PAGE_SIZE: usize = 4096;

#[derive(Clone)]
pub struct MemConfig {
    pub ram: Arc<Ram>,
    pub ram_start: PageNum,
    pub devices: Box<[DeviceEntry]>,
}

impl MemConfig {
    #[allow(clippy::needless_borrow)]
    pub fn find_device_by_page(&self, page: PageNum) -> Option<&DeviceEntry> {
        for entry in self.devices.iter() {
            if page_in_range(page, entry.base, entry.size) {
                return Some(&entry);
            }
        }

        None
    }

    pub fn memory_mapping_type(&self, page: PageNum) -> Option<MemoryMappingType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            Some(MemoryMappingType::RAM)
        } else {
            self.find_device_by_page(page)
                .map(|_x| MemoryMappingType::MMIO)
        }
    }

    pub fn read_dword(&self, page: PageNum, offset: u16) -> Result<DWord, ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.read_dword(page - self.ram_start, offset)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::LoadAccessFault)?;

            entry.interface.read_dword(page - entry.base, offset)
        }
    }
    pub fn read_word(&self, page: PageNum, offset: u16) -> Result<Word, ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.read_word(page - self.ram_start, offset)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::LoadAccessFault)?;

            entry.interface.read_word(page - entry.base, offset)
        }
    }
    pub fn read_hword(&self, page: PageNum, offset: u16) -> Result<HWord, ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.read_hword(page - self.ram_start, offset)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::LoadAccessFault)?;

            entry.interface.read_hword(page - entry.base, offset)
        }
    }
    pub fn read_byte(&self, page: PageNum, offset: u16) -> Result<Byte, ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.read_byte(page - self.ram_start, offset)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::LoadAccessFault)?;

            entry.interface.read_byte(page - entry.base, offset)
        }
    }

    pub fn write_dword(
        &self,
        page: PageNum,
        offset: u16,
        value: DWord,
    ) -> Result<(), ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.write_dword(page - self.ram_start, offset, value)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::StoreAmoAccessFault)?;
            entry
                .interface
                .write_dword(page - entry.base, offset, value)
        }
    }
    pub fn write_word(&self, page: PageNum, offset: u16, value: Word) -> Result<(), ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.write_word(page - self.ram_start, offset, value)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::StoreAmoAccessFault)?;
            entry.interface.write_word(page - entry.base, offset, value)
        }
    }
    pub fn write_hword(
        &self,
        page: PageNum,
        offset: u16,
        value: HWord,
    ) -> Result<(), ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.write_hword(page - self.ram_start, offset, value)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::StoreAmoAccessFault)?;
            entry
                .interface
                .write_hword(page - entry.base, offset, value)
        }
    }
    pub fn write_byte(&self, page: PageNum, offset: u16, value: Byte) -> Result<(), ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            self.ram.write_byte(page - self.ram_start, offset, value)
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::StoreAmoAccessFault)?;
            entry.interface.write_byte(page - entry.base, offset, value)
        }
    }

    pub fn get_atomic_dword(
        &self,
        page: PageNum,
        offset: u16,
    ) -> Result<&AtomicU64, ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            debug_assert!(((offset * 8) as usize) < PAGE_SIZE);
            let index = page * (PAGE_SIZE / 8) + (offset as usize);
            unsafe {
                self.ram
                    .buf_transmuted::<AtomicU64>()
                    .get(index)
                    .ok_or(ExceptionType::HardwareError)
            }
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::StoreAmoAccessFault)?;
            entry.interface.get_atomic_dword(page - entry.base, offset)
        }
    }
    pub fn get_atomic_word(&self, page: PageNum, offset: u16) -> Result<&AtomicU32, ExceptionType> {
        if page_in_range(page, self.ram_start, self.ram.pages) {
            debug_assert!(((offset * 4) as usize) < PAGE_SIZE);
            let index = page * (PAGE_SIZE / 4) + (offset as usize);
            unsafe {
                self.ram
                    .buf_transmuted::<AtomicU32>()
                    .get(index)
                    .ok_or(ExceptionType::HardwareError)
            }
        } else {
            let entry = self
                .find_device_by_page(page)
                .ok_or(ExceptionType::StoreAmoAccessFault)?;
            entry.interface.get_atomic_word(page - entry.base, offset)
        }
    }
}

fn page_in_range(page: PageNum, start: PageNum, pages: PageNum) -> bool {
    page >= start && page - start < pages
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MemoryMappingType {
    MMIO,
    RAM,
}

pub struct Ram {
    buf: MmapMut,
    pages: PageNum,
}

#[cfg(target_endian = "big")]
compile_error!("Current RAM implementation requires a little-endian host.");

impl Ram {
    pub fn try_new(pages: PageNum) -> Result<Self, std::io::Error> {
        Ok(Self {
            buf: MmapMut::map_anon(pages * PAGE_SIZE)?,
            pages,
        })
    }

    pub fn buf_mut(&mut self) -> &mut [u8] {
        self.buf.as_mut()
    }

    pub fn pages(&self) -> PageNum {
        self.pages
    }

    /// # Safety
    /// Safe if T has a size divisible by page size (4kb) (or is known to have a size divisible by the full ram size) and you know that the RAM is made up of valid naturally aligned values of T
    #[inline]
    pub unsafe fn buf_transmuted<T>(&self) -> &[T] {
        debug_assert!(self.buf.len().is_multiple_of(std::mem::size_of::<T>()));
        unsafe {
            std::slice::from_raw_parts(
                self.buf.as_ptr() as *const T,
                self.buf.len() / std::mem::size_of::<T>(),
            )
        }
    }

    #[inline]
    pub fn buf_atomic(&self) -> &[AtomicU8] {
        unsafe { std::slice::from_raw_parts(self.buf.as_ptr() as *const AtomicU8, self.buf.len()) }
    }

    #[inline]
    pub fn read_dword(&self, page: PageNum, offset: u16) -> Result<DWord, ExceptionType> {
        debug_assert!(((offset * 8) as usize) < PAGE_SIZE);
        let index = page * (PAGE_SIZE / 8) + (offset as usize);
        Ok(unsafe {
            self.buf_transmuted::<AtomicU64>()
                .get(index)
                .ok_or(ExceptionType::LoadAccessFault)
        }?
        .load(Relaxed))
    }
    #[inline]
    pub fn read_word(&self, page: PageNum, offset: u16) -> Result<Word, ExceptionType> {
        debug_assert!(((offset * 4) as usize) < PAGE_SIZE);
        let index = page * (PAGE_SIZE / 4) + (offset as usize);
        Ok(unsafe {
            self.buf_transmuted::<AtomicU32>()
                .get(index)
                .ok_or(ExceptionType::LoadAccessFault)
        }?
        .load(Relaxed))
    }
    #[inline]
    pub fn read_hword(&self, page: PageNum, offset: u16) -> Result<HWord, ExceptionType> {
        debug_assert!(((offset * 2) as usize) < PAGE_SIZE);
        let index = page * (PAGE_SIZE / 2) + (offset as usize);
        Ok(unsafe {
            self.buf_transmuted::<AtomicU16>()
                .get(index)
                .ok_or(ExceptionType::LoadAccessFault)
        }?
        .load(Relaxed))
    }
    #[inline]
    pub fn read_byte(&self, page: PageNum, offset: u16) -> Result<Byte, ExceptionType> {
        debug_assert!((offset as usize) < PAGE_SIZE);
        let index = page * PAGE_SIZE + (offset as usize);
        Ok(self
            .buf_atomic()
            .get(index)
            .ok_or(ExceptionType::LoadAccessFault)?
            .load(Relaxed))
    }

    #[inline]
    pub fn write_dword(
        &self,
        page: PageNum,
        offset: u16,
        value: DWord,
    ) -> Result<(), ExceptionType> {
        debug_assert!(((offset * 8) as usize) < PAGE_SIZE);
        let index = page * (PAGE_SIZE / 8) + (offset as usize);
        unsafe {
            self.buf_transmuted::<AtomicU64>()
                .get(index)
                .ok_or(ExceptionType::StoreAmoAccessFault)
        }?
        .store(value, Relaxed);
        Ok(())
    }
    #[inline]
    pub fn write_word(&self, page: PageNum, offset: u16, value: Word) -> Result<(), ExceptionType> {
        debug_assert!(((offset * 4) as usize) < PAGE_SIZE);
        let index = page * (PAGE_SIZE / 4) + (offset as usize);
        unsafe {
            self.buf_transmuted::<AtomicU32>()
                .get(index)
                .ok_or(ExceptionType::StoreAmoAccessFault)
        }?
        .store(value, Relaxed);
        Ok(())
    }
    #[inline]
    pub fn write_hword(
        &self,
        page: PageNum,
        offset: u16,
        value: HWord,
    ) -> Result<(), ExceptionType> {
        debug_assert!(((offset * 2) as usize) < PAGE_SIZE);
        let index = page * (PAGE_SIZE / 2) + (offset as usize);
        unsafe {
            self.buf_transmuted::<AtomicU16>()
                .get(index)
                .ok_or(ExceptionType::StoreAmoAccessFault)
        }?
        .store(value, Relaxed);
        Ok(())
    }
    #[inline]
    pub fn write_byte(&self, page: PageNum, offset: u16, value: Byte) -> Result<(), ExceptionType> {
        debug_assert!((offset as usize) < PAGE_SIZE);
        let index = page * PAGE_SIZE + (offset as usize);
        self.buf_atomic()
            .get(index)
            .ok_or(ExceptionType::StoreAmoAccessFault)?
            .store(value, Relaxed);
        Ok(())
    }
}

#[derive(Clone)]
pub struct DeviceEntry {
    pub base: PageNum,
    pub size: PageNum,
    pub interface: Arc<dyn MemDeviceInterface>,
}

#[allow(unused_variables)]
pub trait MemDeviceInterface {
    fn write_dword(&self, page: PageNum, offset: u16, value: DWord) -> Result<(), ExceptionType> {
        Err(ExceptionType::StoreAmoAccessFault)
    }
    fn write_word(&self, page: PageNum, offset: u16, value: Word) -> Result<(), ExceptionType> {
        Err(ExceptionType::StoreAmoAccessFault)
    }
    fn write_hword(&self, page: PageNum, offset: u16, value: HWord) -> Result<(), ExceptionType> {
        Err(ExceptionType::StoreAmoAccessFault)
    }
    fn write_byte(&self, page: PageNum, offset: u16, value: Byte) -> Result<(), ExceptionType> {
        Err(ExceptionType::StoreAmoAccessFault)
    }

    fn read_dword(&self, page: PageNum, offset: u16) -> Result<DWord, ExceptionType> {
        Err(ExceptionType::LoadAccessFault)
    }
    fn read_word(&self, page: PageNum, offset: u16) -> Result<Word, ExceptionType> {
        Err(ExceptionType::LoadAccessFault)
    }
    fn read_hword(&self, page: PageNum, offset: u16) -> Result<HWord, ExceptionType> {
        Err(ExceptionType::LoadAccessFault)
    }
    fn read_byte(&self, page: PageNum, offset: u16) -> Result<Byte, ExceptionType> {
        Err(ExceptionType::LoadAccessFault)
    }

    fn get_atomic_word(&self, page: PageNum, offset: u16) -> Result<&AtomicU32, ExceptionType> {
        Err(ExceptionType::StoreAmoAccessFault)
    }
    fn get_atomic_dword(&self, page: PageNum, offset: u16) -> Result<&AtomicU64, ExceptionType> {
        Err(ExceptionType::StoreAmoAccessFault)
    }
}