ph00524: add emulator

modules/ph00524/emu/arbiters.go

@@ -0,0 +1,98 @@
+package main
+
+import (
+	"log"
+
+	"github.com/koron-go/z80"
+)
+
+// ioPeripheral is a z80.IO device at a given address.
+type ioPeripheral struct {
+	start      uint8
+	length     uint8
+	peripheral z80.IO
+}
+
+// ioArbiter is a collection of I/O devices at addresses. It implements z80.IO
+// itself, dispatching to the appropriate device as needed.
+type ioArbiter struct {
+	peripherals []*ioPeripheral
+}
+
+func (i *ioArbiter) get(addr uint8) *ioPeripheral {
+	for _, periph := range i.peripherals {
+		if addr < periph.start {
+			continue
+		}
+		if addr > periph.start+periph.length {
+			continue
+		}
+		return periph
+	}
+	return nil
+}
+
+func (i *ioArbiter) In(addr uint8) uint8 {
+	p := i.get(addr)
+	if p == nil {
+		log.Fatalf("Unhandled I/O In at %02x", addr)
+		return 0
+	}
+	return p.peripheral.In(addr - p.start)
+}
+func (i *ioArbiter) Out(addr uint8, value uint8) {
+	p := i.get(addr)
+	if p == nil {
+		log.Fatalf("Unhandled I/O Out at %02x", addr)
+		return
+	}
+	p.peripheral.Out(addr-p.start, value)
+}
+
+// memory is a continuous memory region at a given address, optionally marked
+// read only.
+type memory struct {
+	start    uint16
+	data     []uint8
+	readonly bool
+}
+
+// memoryArbiter implements Z80.Memory and dispatches accesses to subordinate
+// memory instances.
+type memoryArbiter struct {
+	memories []memory
+}
+
+func (m *memoryArbiter) get(addr uint16) *memory {
+	for _, mem := range m.memories {
+		if addr < mem.start {
+			continue
+		}
+		if addr >= mem.start+uint16(len(mem.data)) {
+			continue
+		}
+		return &mem
+	}
+	return nil
+}
+
+func (m *memoryArbiter) Get(addr uint16) uint8 {
+	mem := m.get(addr)
+	if mem == nil {
+		log.Fatalf("Unhandled memory Get at %04x", addr)
+		return 0
+	}
+	return mem.data[addr-mem.start]
+}
+
+func (m *memoryArbiter) Set(addr uint16, value uint8) {
+	mem := m.get(addr)
+	if mem == nil {
+		log.Fatalf("Unhandled memory Set at %04x", addr)
+		return
+	}
+	if mem.readonly {
+		log.Fatalf("Read-only memory Set at %04x", addr)
+	}
+	mem.data[addr-mem.start] = value
+}