From bb8162c22e34ac588f92b4d3783c39d04a67ec2c Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Mon, 4 Jan 2016 14:19:56 -0700
Subject: Fix cache sharing bug

---
 src/lib.rs       |  6 ++++--
 src/memory.rs    |  6 +++++-
 src/simulator.rs | 30 +++++++++++++++++-------------
 3 files changed, 26 insertions(+), 16 deletions(-)

(limited to 'src')

diff --git a/src/lib.rs b/src/lib.rs
index c3fa51b..35951c2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -51,14 +51,16 @@ fn test_elfloader() {
     let (data, data_offset) = data.unwrap();
 
     let mmu = memory::IdentityMmu::new();
+    // TODO: make this a method; have it accept a MMU
     let memory = memory::Memory::new_from_text_and_data(
         0x8000,
         text, text_offset as usize,
         data, data_offset as usize);
     let memory_ref = Rc::new(RefCell::new(Box::new(memory) as Box<memory::MemoryInterface>));
     let cache = Rc::new( RefCell::new( Box::new( memory::DirectMappedCache::new(4, 4, memory_ref.clone())) as Box<memory::MemoryInterface>) );
-    let core = simulator::Core::new(start, cache.clone(), Box::new(mmu));
-    let mut simulator = simulator::Simulator::new(vec![core], memory_ref.clone());
+    let core = simulator::Core::new(start, 0x1000, cache.clone(), Box::new(mmu));
+    let core2 = simulator::Core::new(start, 0x3000, cache.clone(), Box::new(memory::IdentityMmu::new()));
+    let mut simulator = simulator::Simulator::new(vec![core, core2], memory_ref.clone());
     simulator.run();
 }
 
diff --git a/src/memory.rs b/src/memory.rs
index db0dca4..9bc3643 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -307,8 +307,12 @@ impl<'a> MemoryInterface for DirectMappedCache<'a> {
     fn step(&mut self) {
         for set in self.cache.iter_mut() {
             if let Some(ref mut fetch_request) = set.fetch_request {
-                if fetch_request.cycles_left > 0 {
+                // Start filling the cache once the cycles_left would
+                // have hit 0, so that the consumer never gets
+                // stall_cycles = 0
+                if fetch_request.cycles_left > 1 {
                     fetch_request.cycles_left -= 1;
+                    return;
                 }
                 // read all the words in a line from the next
                 // level, until we get a stall
diff --git a/src/simulator.rs b/src/simulator.rs
index 571fafe..38e8f88 100644
--- a/src/simulator.rs
+++ b/src/simulator.rs
@@ -28,6 +28,8 @@ pub struct Core<'a>{
     running: bool,
     cache: SharedMemory<'a>,
     mmu: Box<Mmu + 'a>,
+    cycle_count: u32,
+    stall_count: u32,
 }
 
 pub struct Simulator<'a> {
@@ -75,22 +77,30 @@ impl RegisterFile {
 
 impl<'a> Core<'a> {
     // TODO: take Rc<RefCell<>> to Memory as well?
-    pub fn new(entry: isa::Address, cache: SharedMemory<'a>, mmu: Box<Mmu + 'a>) -> Core<'a> {
+    pub fn new(entry: isa::Address, sp: isa::Address,
+               cache: SharedMemory<'a>, mmu: Box<Mmu + 'a>) -> Core<'a> {
+        let mut registers = RegisterFile::new();
+        registers.write_word(isa::Register::X2, sp);
         Core {
             pc: entry,
-            registers: RegisterFile::new(),
+            registers: registers,
             stall: 0,
             running: true,
             cache: cache,
             mmu: mmu,
+            cycle_count: 0,
+            stall_count: 0,
         }
     }
 
     fn step(&mut self, inst: isa::Instruction) {
         let pc = self.pc;
 
+        self.cycle_count += 1;
+
         if self.stall > 0 {
             self.stall -= 1;
+            self.stall_count += 1;
             return;
         }
 
@@ -279,8 +289,7 @@ impl<'a> Core<'a> {
 
                     let result = self.cache.borrow_mut().read_word(address);
                     match result {
-                        Ok(value) =>
-                            self.registers.write_word(inst.rd(), value),
+                        Ok(value) => self.registers.write_word(inst.rd(), value),
                         Err(MemoryError::CacheMiss { stall_cycles }) => {
                             self.stall = stall_cycles;
                             return;
@@ -310,7 +319,7 @@ impl<'a> Core<'a> {
                     match result {
                         Ok(()) => (),
                         Err(MemoryError::CacheMiss { stall_cycles }) => {
-                            self.stall = stall_cycles;
+                            self.stall = stall_cycles - 1;
                             return;
                         },
                         Err(MemoryError::InvalidAddress) => {
@@ -352,7 +361,6 @@ impl<'a> Core<'a> {
 impl<'a> Simulator<'a> {
     pub fn new(cores: Vec<Core<'a>>, memory: SharedMemory<'a>)
                -> Simulator<'a> {
-        // TODO: pass in GP, SP, _start
         // TODO: initialize GP, registers (GP is in headers)
         Simulator {
             cores: cores,
@@ -361,18 +369,12 @@ impl<'a> Simulator<'a> {
     }
 
     pub fn run(&mut self) {
-        // hardcode SP
-        self.cores[0].registers.write_word(isa::Register::X2, 0x7FFC);
-        let mut total_cycles = 0;
-        let mut stall_cycles = 0;
         loop {
             let mut ran = false;
-            total_cycles += 1;
             for core in self.cores.iter_mut() {
                 if !core.running {
                     continue;
                 }
-                if core.stall > 0 { stall_cycles += 1; }
 
                 let pc = core.pc;
                 let pc = core.mmu.translate(pc);
@@ -390,7 +392,9 @@ impl<'a> Simulator<'a> {
             }
             if !ran {
                 println!("All cores are not running, stopping...");
-                println!("Stalled cycles: {} of {}", stall_cycles, total_cycles);
+                for (i, core) in self.cores.iter().enumerate() {
+                    println!("Core {}: stalled {} of {}", i, core.stall_count, core.cycle_count);
+                }
                 break;
             }
         }
-- 
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