From 29a94dd442f88d4cc53d79b9627bb6c9a8a2e22d Mon Sep 17 00:00:00 2001
From: mappu <mappu04@gmail.com>
Date: Wed, 28 Dec 2022 13:59:35 +1300
Subject: [PATCH] cpu: use EEI terminology

---
 cmd/riscvrun/main.go |  2 +-
 cpu.go               |  4 ++--
 cpu_test.go          |  2 +-
 memoryWorld.go       | 45 ------------------------------------------
 virtualEei.go        | 47 ++++++++++++++++++++++++++++++++++++++++++++
 world.go             |  4 +++-
 6 files changed, 54 insertions(+), 50 deletions(-)
 delete mode 100644 memoryWorld.go
 create mode 100644 virtualEei.go

diff --git a/cmd/riscvrun/main.go b/cmd/riscvrun/main.go
index 9c02259..2e59675 100644
--- a/cmd/riscvrun/main.go
+++ b/cmd/riscvrun/main.go
@@ -20,7 +20,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	sw := riscvemu.MemoryWorld{
+	sw := riscvemu.VirtualEEI{
 		Ram: make([]byte, *memorySize),
 	}
 
diff --git a/cpu.go b/cpu.go
index 70cf04d..1695baf 100644
--- a/cpu.go
+++ b/cpu.go
@@ -11,10 +11,10 @@ func (e ErrInvalidOpcode) Error() string { return "invalid opcode" }
 type CPUState struct {
 	Registers [32]uint32
 	Pc        uint32
-	w         World
+	w         EEI
 }
 
-func NewCPU(w World) CPUState {
+func NewCPU(w EEI) CPUState {
 	return CPUState{w: w}
 }
 
diff --git a/cpu_test.go b/cpu_test.go
index cb89695..c9a58e0 100644
--- a/cpu_test.go
+++ b/cpu_test.go
@@ -6,7 +6,7 @@ import (
 
 func TestCPU(t *testing.T) {
 
-	sw := MemoryWorld{
+	sw := VirtualEEI{
 		Ram: make([]byte, 1024),
 	}
 	_ = sw.Write32(0, 0b00000000000100000000000001110011) // EBREAK
diff --git a/memoryWorld.go b/memoryWorld.go
deleted file mode 100644
index 3684ee4..0000000
--- a/memoryWorld.go
+++ /dev/null
@@ -1,45 +0,0 @@
-package riscvemu
-
-type MemoryWorld struct {
-	Ram []byte
-}
-
-func (mw *MemoryWorld) ReadByte(addr uint32) (byte, error) {
-	if addr >= uint32(len(mw.Ram)) {
-		panic("out of bounds")
-	}
-
-	return mw.Ram[addr], nil
-}
-
-func (mw *MemoryWorld) Read32(addr uint32) (uint32, error) {
-	// n.b. will panic on overflow
-	return (uint32(mw.Ram[addr]) << 24) | (uint32(mw.Ram[addr+1]) << 16) | (uint32(mw.Ram[addr+2]) << 8) | uint32(mw.Ram[addr+3]), nil
-}
-
-func (mw *MemoryWorld) WriteByte(addr uint32, value byte) error {
-	if addr >= uint32(len(mw.Ram)) {
-		panic("out of bounds")
-	}
-
-	mw.Ram[addr] = value
-	return nil
-}
-
-func (mw *MemoryWorld) Write32(addr, value uint32) error {
-	// n.b. will panic on overflow
-	mw.Ram[addr] = byte((value >> 24) & 0b11111111)
-	mw.Ram[addr+1] = byte((value >> 16) & 0b11111111)
-	mw.Ram[addr+2] = byte((value >> 8) & 0b11111111)
-	mw.Ram[addr+3] = byte(value & 0b11111111)
-
-	return nil
-}
-
-func (mw *MemoryWorld) Syscall() {
-	panic("syscall")
-}
-
-func (mw *MemoryWorld) Trap() (bool, error) {
-	panic("trap")
-}
diff --git a/virtualEei.go b/virtualEei.go
new file mode 100644
index 0000000..1ace7ac
--- /dev/null
+++ b/virtualEei.go
@@ -0,0 +1,47 @@
+package riscvemu
+
+type VirtualEEI struct {
+	Ram []byte
+}
+
+func (ve *VirtualEEI) ReadByte(addr uint32) (byte, error) {
+	if addr >= uint32(len(ve.Ram)) {
+		panic("out of bounds")
+	}
+
+	return ve.Ram[addr], nil
+}
+
+func (ve *VirtualEEI) Read32(addr uint32) (uint32, error) {
+	// n.b. will panic on overflow
+	// RISC-V allows 32-bit load/stores to be implemented as either little-endian
+	// or big-endian. This is the little-endian version
+	return (uint32(ve.Ram[addr]) << 24) | (uint32(ve.Ram[addr+1]) << 16) | (uint32(ve.Ram[addr+2]) << 8) | uint32(ve.Ram[addr+3]), nil
+}
+
+func (ve *VirtualEEI) WriteByte(addr uint32, value byte) error {
+	if addr >= uint32(len(ve.Ram)) {
+		panic("out of bounds")
+	}
+
+	ve.Ram[addr] = value
+	return nil
+}
+
+func (ve *VirtualEEI) Write32(addr, value uint32) error {
+	// n.b. will panic on overflow
+	ve.Ram[addr] = byte((value >> 24) & 0b11111111)
+	ve.Ram[addr+1] = byte((value >> 16) & 0b11111111)
+	ve.Ram[addr+2] = byte((value >> 8) & 0b11111111)
+	ve.Ram[addr+3] = byte(value & 0b11111111)
+
+	return nil
+}
+
+func (ve *VirtualEEI) Syscall() {
+	panic("syscall")
+}
+
+func (ve *VirtualEEI) Trap() (bool, error) {
+	panic("trap")
+}
diff --git a/world.go b/world.go
index 4276a7b..31aa592 100644
--- a/world.go
+++ b/world.go
@@ -1,6 +1,8 @@
 package riscvemu
 
-type World interface {
+// EEI (Execution Environment Interface) is the enivronment in which RISC-V
+// code is run.
+type EEI interface {
 	ReadByte(addr uint32) (byte, error)
 	Read32(addr uint32) (uint32, error)
 	WriteByte(addr uint32, value byte) error