path: root/src/shareable_cache.rs

use std::collections::HashSet;

use rustv::cache::{CacheInterface, CacheMetadata, SharedCache};
use rustv::isa::{self, IsaType};
use rustv::memory::{MemoryError, MemoryInterface, Result};

pub const WRITE_TRAP_VALUE: isa::Byte = isa::Byte(0xE0);
pub const AREA_TRAP_VALUE: isa::Byte = isa::Byte(0xE4);

pub const WRITE_TRAP_STALL: u32 = 1_000_000;
pub const WRITE_TRAP_SET_STALL: u32 = 100;

/// A cache that can be used as two separate caches or one
/// set-associative cache.
pub struct ShareableCache<'a> {
    core_id: usize,
    primary: SharedCache<'a>,
    secondary: SharedCache<'a>,
    secondary_enabled: bool,
    use_secondary: bool,
    traps_hit: HashSet<isa::Address>,
}

/// Cache snooping: update the secondary cache when the primary cache
/// is written to. This is a macro in order to be generic with regard
/// to the size of the write.
// TODO: snoop needs to take care of in-flight fetch requests?
macro_rules! snoop {
    ($cache: expr, $write_value: ident, $address: ident, $value: ident) => {
        if $cache.borrow().is_address_accessible($address) {
            // depends on invariant: write_word completes instantly
            // when the address is accessible (in-cache)
            let _ = $cache.borrow_mut().$write_value($address, $value);
        }
    }
}

/// Check whether the write sets off any traps, and stall if
/// appropriate. This is a macro in order to be generic with regard to
/// the size of the write.
macro_rules! check_traps {
    ($core_id: expr, $cache: expr, $traps_hit: expr, $write_value: ident,
     $address: ident, $value: ident) => {{
        // Requires invariant: if x is the address of a word, x + 0 is
        // the address of the LSB and x + 3 is the address of the MSB.

        let accessible = {
            $cache.borrow().is_address_accessible($address)
        };

        if accessible {
            // No stall - check for trap
            let old_value = {
                $cache.borrow_mut().read_word($address)
            };

            match old_value {
                Ok(old_value) => {
                    let old_bytes = old_value.as_bytes();
                    let new_bytes = $value.as_bytes();

                    let mut num_traps_hit = 0;
                    let mut num_traps_set = 0;

                    let iter = old_bytes.iter()
                        // Skip {offset} bytes
                        .skip(($address.0 & 0x3) as usize)
                        .take(new_bytes.len())
                        .zip(new_bytes.iter())
                        .enumerate();
                    for (offset, (old, new)) in iter {
                        // Make sure offset bits are cleared before
                        // adding offset
                        let trap_address = ($address & 0xFFFFFFFC) +
                            isa::Word(offset as u32);
                        if *old == WRITE_TRAP_VALUE &&
                            !$traps_hit.contains(&trap_address) {
                                num_traps_hit += 1;
                                $traps_hit.insert(trap_address);
                            }
                        else if *old != WRITE_TRAP_VALUE {
                            $traps_hit.remove(&trap_address);
                        }

                        if *new == WRITE_TRAP_VALUE &&
                            (*old != WRITE_TRAP_VALUE ||
                             $traps_hit.contains(&trap_address)) {
                            $traps_hit.remove(&trap_address);
                            num_traps_set += 1;
                        }
                    }

                    if num_traps_hit > 0 {
                        info!("[memory] core {}: {} write trap(s) hit at address {:x},\
                               stalling for 1_000_000 cycles each",
                              $core_id, num_traps_hit, $address);
                        Err(MemoryError::CacheMiss {
                            stall_cycles: num_traps_hit * WRITE_TRAP_STALL,
                            retry: true,
                        })
                    }
                    else {
                        // Use retry: false to induce a stall iff the
                        // write succeeded
                        let result =
                            $cache.borrow_mut().$write_value($address, $value);

                        if num_traps_set > 0 {
                            match result {
                                Ok(()) => {
                                    info!("[memory] core {}: {} write trap(s) set at address {:x},\
                                           stalling for 100 cycles each",
                                          $core_id, num_traps_set, $address);
                                    Err(MemoryError::CacheMiss {
                                        stall_cycles: num_traps_set *
                                            WRITE_TRAP_SET_STALL,
                                        retry: false,
                                    })
                                },
                                _ => result
                            }
                        }
                        else {
                            result
                        }
                    }
                }
                Err(e) => {
                    panic!("Could not read accessible value: {:?}", e)
                }
            }
        }
        else {
            // Not in cache - defer to fetch
            $cache.borrow_mut().$write_value($address, $value)
        }
    }}
}

macro_rules! write_value {
    ($self_: ident, $write_value: ident, $address: ident, $value: ident) => {
        if $self_.secondary_enabled {
            let (primary_accessible, secondary_accessible) =
                $self_.address_accessible($address);

            if primary_accessible {
                snoop!($self_.secondary, $write_value, $address, $value);
                check_traps!($self_.core_id, $self_.primary,
                             &mut $self_.traps_hit,
                             $write_value, $address, $value)
            }
            else if secondary_accessible {
                snoop!($self_.primary, $write_value, $address, $value);
                check_traps!($self_.core_id, $self_.secondary,
                             &mut $self_.traps_hit,
                             $write_value, $address, $value)
            }
            else {
                $self_.use_secondary = !$self_.use_secondary;
                if $self_.use_secondary {
                    snoop!($self_.primary, $write_value, $address, $value);
                    check_traps!($self_.core_id, $self_.secondary,
                                 &mut $self_.traps_hit,
                                 $write_value, $address, $value)
                }
                else {
                    snoop!($self_.secondary, $write_value, $address, $value);
                    check_traps!($self_.core_id, $self_.primary,
                                 &mut $self_.traps_hit,
                                 $write_value, $address, $value)
                }
            }
        }
        else {
            snoop!($self_.secondary, $write_value, $address, $value);
            check_traps!($self_.core_id, $self_.primary,
                         &mut $self_.traps_hit,
                         $write_value, $address, $value)
        }
    }
}

impl<'a> ShareableCache<'a> {
    pub fn new(core_id: usize,
               cache1: SharedCache<'a>, cache2: SharedCache<'a>)
               -> ShareableCache<'a> {
        ShareableCache {
            core_id: core_id,
            primary: cache1.clone(),
            secondary: cache2.clone(),
            secondary_enabled: false,
            use_secondary: false,
            traps_hit: HashSet::new(),
        }
    }

    pub fn enable_secondary(&mut self) {
        self.secondary_enabled = true;
        self.use_secondary = true;
    }

    pub fn disable_secondary(&mut self) {
        self.secondary_enabled = false;
    }

    fn address_accessible(&self, address: isa::Address) -> (bool, bool) {
        // Use scopes to make sure these borrows end before the
        // branches of the if statement begin
        let primary_accessible = {
            self.primary.borrow().is_address_accessible(address)
        };
        let secondary_accessible = {
            self.secondary.borrow().is_address_accessible(address)
        };

        (primary_accessible, secondary_accessible)
    }
}

impl<'a> MemoryInterface for ShareableCache<'a> {
    fn latency(&self) -> u32 {
        self.primary.borrow().latency()
    }

    fn step(&mut self) {
        // We only step the primary cache. The idea is that the
        // secondary cache should be the primary cache of another
        // ShareableCache.
        self.primary.borrow_mut().step();
    }

    fn is_address_accessible(&self, address: isa::Address) -> bool {
        self.primary.borrow().is_address_accessible(address) ||
            (self.secondary_enabled &&
             self.secondary.borrow().is_address_accessible(address))
    }

    fn read_word(&mut self, address: isa::Address) -> Result<isa::Word> {
        // TODO: disallow access to high or low memory unless
        // secondary cache is enabled. Remember: addresses are already
        // translated

        // TODO: is CacheRacer physically or virtually addressed?
        if self.secondary_enabled {
            let (primary_accessible, secondary_accessible) =
                self.address_accessible(address);

            if primary_accessible {
                self.primary.borrow_mut().read_word(address)
            }
            else if secondary_accessible {
                self.secondary.borrow_mut().read_word(address)
            }
            else {
                self.use_secondary = !self.use_secondary;
                if self.use_secondary {
                    self.secondary.borrow_mut().read_word(address)
                }
                else {
                    self.primary.borrow_mut().read_word(address)
                }
            }
        }
        else {
            self.primary.borrow_mut().read_word(address)
        }
    }

    fn write_word(&mut self, address: isa::Address, value: isa::Word) -> Result<()> {
        write_value!(self, write_word, address, value)
    }

    fn write_halfword(&mut self, address: isa::Address, value: isa::HalfWord) -> Result<()> {
        write_value!(self, write_halfword, address, value)
    }

    fn write_byte(&mut self, address: isa::Address, value: isa::Byte) -> Result<()> {
        write_value!(self, write_byte, address, value)
    }
}

impl<'a> CacheInterface for ShareableCache<'a> {
    fn cache_metadata(&self) -> CacheMetadata {
        // TODO: merge tags in secondary enabled mode
        self.primary.borrow().cache_metadata()
    }
}