From f373d547bbc2431e9e66fa352b494cf70d732d0e Mon Sep 17 00:00:00 2001
From: exuanbo <exuanbo@protonmail.com>
Date: Tue, 1 Oct 2024 20:44:24 +0100
Subject: [PATCH] feat(core): add basic bus, memory, and cpu impl

---
 src/core/bus/bus.ts       | 52 +++++++++++++++++++++++++++++++++
 src/core/cpu/cpu.ts       | 43 ++++++++++++++++++++++++++++
 src/core/memory/memory.ts | 60 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 155 insertions(+)
 create mode 100644 src/core/bus/bus.ts
 create mode 100644 src/core/cpu/cpu.ts
 create mode 100644 src/core/memory/memory.ts

diff --git a/src/core/bus/bus.ts b/src/core/bus/bus.ts
new file mode 100644
index 00000000..66876e19
--- /dev/null
+++ b/src/core/bus/bus.ts
@@ -0,0 +1,52 @@
+import { asapScheduler, BehaviorSubject, filter, observeOn, shareReplay, skipWhile } from 'rxjs'
+
+export const enum Control {
+  CLOCK_IDLE   = 0b0000,
+  MEMORY_READ  = 0b1000,
+  IO_READ      = 0b1001,
+  MEMORY_WRITE = 0b1010,
+  IO_WRITE     = 0b1011,
+  INTERRUPT    = 0b1100,
+}
+
+export interface Signals {
+  data: number
+  address: number
+  control: Control
+}
+
+const initialSignals: Signals = {
+  data: 0x00,
+  address: 0x00,
+  control: Control.CLOCK_IDLE,
+}
+
+export class Bus {
+  private readonly source$ = new BehaviorSubject(initialSignals)
+
+  private readonly shared$ = this.source$.pipe(
+    observeOn(asapScheduler),
+    shareReplay(1),
+  )
+
+  get signals$() {
+    return this.shared$
+  }
+
+  get idle$() {
+    return this.shared$.pipe(
+      filter((signals) => (signals.control === Control.CLOCK_IDLE)),
+    )
+  }
+
+  put(next: Partial<Signals>) {
+    const nextSignals = {
+      ...this.source$.getValue(),
+      ...next,
+    }
+    this.source$.next(nextSignals)
+    return this.shared$.pipe(
+      skipWhile((signals) => (signals !== nextSignals)),
+    )
+  }
+}
diff --git a/src/core/cpu/cpu.ts b/src/core/cpu/cpu.ts
new file mode 100644
index 00000000..cdc64b46
--- /dev/null
+++ b/src/core/cpu/cpu.ts
@@ -0,0 +1,43 @@
+import { filter, firstValueFrom, map, skipUntil } from 'rxjs'
+
+import { type Bus, Control, type Signals } from '../bus/bus'
+
+export class Cpu {
+  constructor(
+    private readonly bus: Bus,
+  ) {
+    this.bus.signals$.pipe(
+      filter((signals) => (signals.control === Control.INTERRUPT)),
+    ).subscribe(this.handleInterrupt)
+  }
+
+  async step() {
+    // TODO: implement step
+    // const opcode = await this.readMemory(...)
+  }
+
+  private readMemory(address: number) {
+    const data$ = this.bus.put({
+      address,
+      control: Control.MEMORY_READ,
+    }).pipe(
+      skipUntil(this.bus.idle$),
+      map((signals) => signals.data),
+    )
+    return firstValueFrom(data$)
+  }
+
+  private writeMemory(address: number, data: number) {
+    const complete$ = this.bus.put({
+      data,
+      address,
+      control: Control.MEMORY_WRITE,
+    })
+    return firstValueFrom(complete$)
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  private handleInterrupt = (_signals: Signals) => {
+    // TODO: implement interrupt handling
+  }
+}
diff --git a/src/core/memory/memory.ts b/src/core/memory/memory.ts
new file mode 100644
index 00000000..a5dc6f88
--- /dev/null
+++ b/src/core/memory/memory.ts
@@ -0,0 +1,60 @@
+import { filter, map, type Observable, share, tap } from 'rxjs'
+
+import { type Bus, Control, type Signals } from '../bus/bus'
+
+export class Memory {
+  // TODO: use shared constants
+  private readonly data = new Uint8Array(0x100)
+
+  private readonly read$: Observable<Signals>
+  private readonly write$: Observable<Signals>
+
+  constructor(
+    private readonly bus: Bus,
+  ) {
+    this.read$ = this.bus.signals$.pipe(
+      filter((signals) => signals.control === Control.MEMORY_READ),
+      tap(this.read),
+      share(),
+    )
+
+    this.write$ = this.bus.signals$.pipe(
+      filter((signals) => signals.control === Control.MEMORY_WRITE),
+      tap(this.write),
+      share(),
+    )
+
+    this.read$.subscribe()
+    this.write$.subscribe()
+  }
+
+  private read = (signals: Signals) => {
+    this.bus.put({
+      data: this.data[signals.address],
+      control: Control.CLOCK_IDLE,
+    })
+  }
+
+  private write = (signals: Signals) => {
+    this.data[signals.address] = signals.data
+    this.bus.put({
+      control: Control.CLOCK_IDLE,
+    })
+  }
+
+  get data$() {
+    return this.write$.pipe(map(() => this.getData()))
+  }
+
+  getData() {
+    return Array.from(this.data)
+  }
+
+  load(data: Uint8Array, offset: number) {
+    this.data.set(data, offset)
+  }
+
+  reset() {
+    this.data.fill(0)
+  }
+}