Load pages to and from drive

hal/paging.go

@@ -67,7 +67,7 @@ func (mmu *MMU) Load(page *Page) {
 		}
 	}
 
-	page.RegisterAddress = mmu.findEmptyRegisterAddress()
+	mmu.loadPageFromDrive(page)
 
 	mmu.LoadedPages = append(mmu.LoadedPages, page)
 }
@@ -89,8 +89,19 @@ func (mmu *MMU) findEmptyRegisterAddress() *uint16 {
 func (mmu *MMU) movePageToDrive(page *Page) {
 
 	for i := 0; i < PageSize-1; i++ {
-		mmu.drive[page.Address][i] = mmu.Registers[i+int(*page.RegisterAddress)*PageSize]
+		mmu.drive[page.Address][i] = mmu.Registers[i+page.RegisterOffset()]
 	}
 
 	page.RegisterAddress = nil
 }
+
+func (mmu *MMU) loadPageFromDrive(page *Page) {
+	for i := 0; i < PageSize-1; i++ {
+		mmu.Registers[i+page.RegisterOffset()] = mmu.drive[page.Address][i]
+	}
+	page.RegisterAddress = mmu.findEmptyRegisterAddress()
+}
+
+func (page *Page) RegisterOffset() int {
+	return int(*page.RegisterAddress) * PageSize
+}