Fetch stage properly holds objects until parent is ready

6 files changed, 32 insertions, 14 deletions

diff --git a/inc/ex.h b/inc/ex.h
index c7b7663..e67980d 100644
--- a/inc/ex.h
+++ b/inc/ex.h
@@ -14,7 +14,7 @@ class EX : public Stage
 	 */
 	EX(Stage *next);
 
-	Response advance(InstrDTO &i, Response p) override;
+	Response advance(InstrDTO &next_instr, Response p) override;
 };
 
 #endif /* EX_H_INCLUDED */
diff --git a/inc/id.h b/inc/id.h
index 95dde37..34e1a47 100644
--- a/inc/id.h
+++ b/inc/id.h
@@ -15,7 +15,7 @@ class ID : public Stage
 	 */
 	ID(Stage *next);
 
-	Response advance(InstrDTO &i, Response p) override;
+	Response advance(InstrDTO &next_instr, Response p) override;
 
 	/**
 	 * Parse an instruction into a type, opcode, and fields. If the type is
diff --git a/inc/if.h b/inc/if.h
index a6869f7..9f84e51 100644
--- a/inc/if.h
+++ b/inc/if.h
@@ -15,7 +15,17 @@ class IF : public Stage
 	 */
 	IF(Stage *next);
 
-	Response advance(InstrDTO &i, Response p) override;
+	Response advance(InstrDTO &next_instr, Response p) override;
+
+  private:
+	/**
+	 * Performs a fetch only if a current fetch is not pending. Pending means
+	 * that a fetch has completed successfully, but the caller stage in the
+	 * pipeline is not ready to receive it. In this case, `curr_instr` is not
+	 * the nullptr.
+	 * @return STALLED if we are waiting on the storage devices, OK otherwise.
+	 */
+	void fetch_with_buffer();
 };
 
 #endif /* IF_H_INCLUDED */
diff --git a/inc/mm.h b/inc/mm.h
index edee589..0d2ce82 100644
--- a/inc/mm.h
+++ b/inc/mm.h
@@ -14,7 +14,7 @@ class MM : public Stage
 	 */
 	MM(Stage *next);
 
-	Response advance(InstrDTO &i, Response p) override;
+	Response advance(InstrDTO &next_instr, Response p) override;
 };
 
 #endif /* MM_H_INCLUDED */
diff --git a/inc/stage.h b/inc/stage.h
index 761b9f6..ff4455b 100644
--- a/inc/stage.h
+++ b/inc/stage.h
@@ -7,6 +7,7 @@
 #include "storage.h"
 #include <array>
 #include <set>
+#include <memory>
 
 class Stage
 {
@@ -17,17 +18,16 @@ class Stage
 	 * @return A newly allocated stage object.
 	 */
 	Stage(Stage *next);
-	virtual ~Stage() = default;
+	virtual ~Stage();
 	/**
 	 * Advances this stage by a single clock cycle.
-	 * @param a DTO object containing various information about an instruction
-	 * moving through the pipeline.
+	 * @param a DTO object containing the next instruction to be processed.
 	 * @param a response, indicating whether or not the parent pipe stage is
-	 * busy.
+	 * ready to accept a new instruction object next cycle.
 	 * @return a response, indicating whether this pipeline stage is stalling,
 	 * busy, or done.
 	 */
-	virtual Response advance(InstrDTO &i, Response p) = 0;
+	virtual Response advance(InstrDTO &next_instr, Response p) = 0;
 
   protected:
 	/**
@@ -57,10 +57,6 @@ class Stage
 	 */
 	static unsigned int pc;
 	/**
-	 * A pointer to the next stage in the pipeline.
-	 */
-	Stage *next;
-	/**
 	 * A pointer to the top-level storage device.
 	 */
 	static Storage *storage;
@@ -72,6 +68,18 @@ class Stage
 	 * The current clock cycle.
 	 */
 	static int clock_cycle;
+	/**
+	 * A pointer to the next stage in the pipeline.
+	 */
+	Stage *next;
+	/**
+	 * A pointer to the current instruction this stage is processing.
+	 */
+	std::unique_ptr<InstrDTO> curr_instr;
+	/**
+	 * The current status of this stage.
+	 */
+	Response status;
 
   private:
 	/**
diff --git a/inc/wb.h b/inc/wb.h
index c1a6a32..9a708a6 100644
--- a/inc/wb.h
+++ b/inc/wb.h
@@ -14,7 +14,7 @@ class WB : public Stage
 	 */
 	WB(Stage *next);
 
-	Response advance(InstrDTO &i, Response p) override;
+	Response advance(InstrDTO &next_instr, Response p) override;
 };
 
 #endif /* WB_H_INCLUDED */