feature creep time!

.vscode/settings.json

@@ -2,6 +2,7 @@
     "cSpell.words": [
         "bdizc",
         "NMOS",
+        "NROM",
         "toggleable"
     ]
 }

mm/mmc.go

@@ -0,0 +1,8 @@
+package mm
+
+import "xubiod/6502-experiment/cpu"
+
+type MemMapper interface {
+	SwapCpu(on *cpu.Core) bool
+	StepCpu(along *cpu.Core) bool
+}

mm/nrom.go

@@ -0,0 +1,32 @@
+package mm
+
+import "xubiod/6502-experiment/cpu"
+
+// https://www.nesdev.org/wiki/NROM
+type MemMapperNROM128 struct {
+	PrgRam  []byte
+	PrgRom0 [0x4000]byte
+}
+
+func (m *MemMapperNROM128) SwapCpu(on *cpu.Core) bool {
+	copy(on.Memory[0x8000:0xC000], m.PrgRom0[:])
+	copy(on.Memory[0xC000:], m.PrgRom0[:])
+	return true
+}
+
+func (*MemMapperNROM128) StepCpu(along *cpu.Core) bool { return true }
+
+// https://www.nesdev.org/wiki/NROM
+type MemMapperNROM256 struct {
+	PrgRam  []byte
+	PrgRom0 [0x4000]byte
+	PrgRom1 [0x4000]byte
+}
+
+func (m *MemMapperNROM256) SwapCpu(on *cpu.Core) bool {
+	copy(on.Memory[0x8000:0xC000], m.PrgRom0[:])
+	copy(on.Memory[0xC000:], m.PrgRom1[:])
+	return true
+}
+
+func (*MemMapperNROM256) StepCpu(along *cpu.Core) bool { return true }

runner.go

@@ -1 +1,34 @@
 package experiment
+
+import (
+	"errors"
+	"xubiod/6502-experiment/cpu"
+	"xubiod/6502-experiment/mm"
+)
+
+// A Runner has a CPU Core (cpu.Core) and a memory mapper (an implementation of
+// mm.MemMapper) and runs them together in such a way to ensure they are synced
+// together.
+type Runner struct {
+	CPU       *cpu.Core     // The CPU core to use
+	MemMapper *mm.MemMapper // The memory manager implementation to use
+}
+
+func New(cpu *cpu.Core, mm *mm.MemMapper) (*Runner, error) {
+	if cpu == nil {
+		err := errors.New("core cannot be nil")
+		return nil, err
+	}
+	return &Runner{CPU: cpu, MemMapper: mm}, nil
+}
+
+func (r *Runner) StepOnce() (valid bool) {
+	if r.CPU != nil {
+		valid, _, _ = r.CPU.StepOnce()
+	}
+	if valid && r.MemMapper != nil {
+		valid = valid && (*r.MemMapper).StepCpu(r.CPU)
+		valid = valid && (*r.MemMapper).SwapCpu(r.CPU)
+	}
+	return
+}