initial commit

tridoraemu/mem.go

@@ -0,0 +1,117 @@
+// Copyright 2021-2024 Sebastian Lederer. See the file LICENSE.md for details
+package main
+import (
+	"fmt"
+	"log"
+	"os"
+	"io"
+	"bufio"
+	"encoding/binary"
+	)
+
+const IOStartAddr = 2048
+
+const RAMStartAddr = 4096
+
+const IOSlotSize = 128
+
+const IOSlotCount = 16
+
+type Mem struct {
+	ram [] word
+	iohandler [IOSlotCount] IOHandler
+}
+
+func (m *Mem) wordAddr(byteaddr word) (int, error) {
+	wordaddr := int(byteaddr / 4)
+	if wordaddr >= len(m.ram) {
+		return 0, fmt.Errorf("Invalid address %08X", byteaddr)
+	}
+	return wordaddr, nil
+}
+
+func (m *Mem) initialize(sizewords int) {
+	m.ram = make([] word, sizewords)
+	for i := 0; i < len(m.ram);  i++ {
+		m.ram[i] = 0
+	}
+}
+
+func (m *Mem) loadFromFile(path string, startAddr int) {
+	f, err := os.Open(path)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+
+	buf := make([]byte,4)
+
+	reader := bufio.NewReader(f)
+	count := 0
+	wordaddr := startAddr / 4
+	for {
+		n, e := reader.Read(buf)
+		if e != nil && e != io.EOF {
+			panic(e)
+		}
+		if n < 4 {
+			if n == 2 {
+				m.ram[wordaddr] = word(binary.BigEndian.Uint32(buf) & 0xFFFF0000)
+				count += 2
+			}
+
+			fmt.Printf("%v bytes read at %08X from %v\n", count, startAddr, path)
+			break
+		} else {
+			m.ram[wordaddr] = word(binary.BigEndian.Uint32(buf))
+			// fmt.Printf("%08X %08X\n", addr, m.ram[addr])
+			count += 4
+			wordaddr += 1
+		}
+	}
+}
+
+func (m *Mem) attachIO(h IOHandler, slot int) {
+	if m.iohandler[slot] != nil {
+		log.Panicf("I/O handler %d already attached", slot)
+	}
+
+	m.iohandler[slot] = h
+}
+
+func (m *Mem) read(byteaddr word) (word, error) {
+	if byteaddr >= IOStartAddr && byteaddr < RAMStartAddr {
+		ioslot := (byteaddr - IOStartAddr) / IOSlotSize
+		if m.iohandler[ioslot] != nil {
+			return m.iohandler[ioslot].read(byteaddr)
+		}
+		return 42, nil
+	}
+
+	wordaddr, err := m.wordAddr(byteaddr)
+	if err == nil {
+		return m.ram[wordaddr], err
+	} else {
+		return 0, err
+	}
+}
+
+func (m *Mem) write(value word, byteaddr word) error {
+	if byteaddr < IOStartAddr {
+		return fmt.Errorf("Write to ROM area at %08X value %08X", byteaddr, value)
+	}
+
+	if byteaddr >= IOStartAddr && byteaddr < RAMStartAddr {
+		ioslot := (byteaddr - IOStartAddr) / IOSlotSize
+		if m.iohandler[ioslot] != nil {
+			return m.iohandler[ioslot].write(value, byteaddr)
+		}
+		return nil
+	}
+
+	wordaddr, err := m.wordAddr(byteaddr)
+	if err == nil {
+		m.ram[wordaddr] = value
+	}
+	return err
+}