From 05a9968d6dafb31d0e33590d80f6eb364de50d8a Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Fri, 15 Jan 2016 17:21:00 -0700
Subject: Allow stalls that do not retry instruction

---
 src/isa/mod.rs   |  2 +-
 src/lib.rs       |  2 ++
 src/memory.rs    |  9 +++++++--
 src/simulator.rs | 12 ++++++++----
 4 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/isa/mod.rs b/src/isa/mod.rs
index 6c4bfbc..1ac585b 100644
--- a/src/isa/mod.rs
+++ b/src/isa/mod.rs
@@ -197,7 +197,7 @@ macro_rules! isa_utype {
 
                 let mut bytes = vec![];
                 for offset in 0..mem::size_of::<$utype>() {
-                    bytes.push(Byte(((self.0 >> (8 * offset)) & 0xFF) as u8));
+                    bytes.push(Byte((self.0 >> (8 * offset)) as u8));
                 }
 
                 bytes
diff --git a/src/lib.rs b/src/lib.rs
index a2b12f0..2aee390 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -96,9 +96,11 @@ mod tests {
 
         let stall = Err(MemoryError::CacheMiss {
             stall_cycles: memory.latency(),
+            retry: true,
         });
         let write_stall = Err(MemoryError::CacheMiss {
             stall_cycles: memory.latency(),
+            retry: true,
         });
 
         let memory_ref = Rc::new(RefCell::new(memory));
diff --git a/src/memory.rs b/src/memory.rs
index b9f070b..052ffb7 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -23,7 +23,10 @@ use isa::{self, Instruction, IsaType};
 pub enum MemoryError {
     InvalidAddress,
     CacheMiss {
+        /// How many cycles to stall
         stall_cycles: u32,
+        /// Whether the load or store should be retried
+        retry: bool,
     },
 }
 
@@ -334,7 +337,7 @@ impl<'a> MemoryInterface for DirectMappedCache<'a> {
                             fetch_request.data[offset as usize] = data;
                             fetch_request.waiting_on += 1;
                         },
-                        Err(MemoryError::CacheMiss { stall_cycles }) => {
+                        Err(MemoryError::CacheMiss { stall_cycles, .. }) => {
                             fetch_request.cycles_left = stall_cycles;
                             continue;
                         },
@@ -401,12 +404,14 @@ impl<'a> MemoryInterface for DirectMappedCache<'a> {
             fetch_request.error = None;
 
             return Err(MemoryError::CacheMiss {
-                stall_cycles: fetch_request.cycles_left
+                stall_cycles: fetch_request.cycles_left,
+                retry: true,
             });
         }
 
         Err(MemoryError::CacheMiss {
             stall_cycles: stall,
+            retry: true,
         })
     }
 
diff --git a/src/simulator.rs b/src/simulator.rs
index 63b5eec..41331ef 100644
--- a/src/simulator.rs
+++ b/src/simulator.rs
@@ -290,9 +290,11 @@ impl<'a> Core<'a> {
 
                 match result {
                     Ok(value) => self.registers.write_word(inst.rd(), value),
-                    Err(MemoryError::CacheMiss { stall_cycles }) => {
+                    Err(MemoryError::CacheMiss { stall_cycles, retry }) => {
                         self.stall = stall_cycles - 1;
-                        return;  // don't increment PC
+                        if retry {
+                            return;  // don't increment PC
+                        }
                     },
                     Err(MemoryError::InvalidAddress) => {
                         self.trap(Trap::IllegalRead {
@@ -325,9 +327,11 @@ impl<'a> Core<'a> {
 
                 match result {
                     Ok(()) => (),
-                    Err(MemoryError::CacheMiss { stall_cycles }) => {
+                    Err(MemoryError::CacheMiss { stall_cycles, retry }) => {
                         self.stall = stall_cycles - 1;
-                        return;  // don't increment PC
+                        if retry {
+                            return;  // don't increment PC
+                        }
                     },
                     Err(MemoryError::InvalidAddress) => {
                         self.trap(Trap::IllegalWrite {
-- 
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