2 files changed, 19 insertions, 2 deletions
diff --git a/src/cpu.spec.ts b/src/cpu.spec.ts
new file mode 100644
index 0000000..92df7ee
--- /dev/null
+++ b/src/cpu.spec.ts
@@ -0,0 +1,8 @@
+import { CPU } from './cpu';
+
+describe('cpu', () => {
+  it('should set initial value of SP to the last address of internal SRAM', () => {
+    const cpu = new CPU(new Uint16Array(1024), 0x1000);
+    expect(cpu.SP).toEqual(0x10ff);
+  });
+});
diff --git a/src/cpu.ts b/src/cpu.ts
index 7fc3ba0..ccccdd1 100644
--- a/src/cpu.ts
+++ b/src/cpu.ts
@@ -7,6 +7,8 @@
 
 import { u16, u8 } from './types';
 
+const registerSpace = 0x100;
+
 export interface ICPU {
   readonly data: Uint8Array;
   readonly dataView: DataView;
@@ -25,7 +27,7 @@ export interface ICPUMemoryHooks {
 }
 
 export class CPU implements ICPU {
-  readonly data = new Uint8Array(16384);
+  readonly data: Uint8Array = new Uint8Array(this.sramBytes + registerSpace);
   readonly data16 = new Uint16Array(this.data.buffer);
   readonly dataView = new DataView(this.data.buffer);
   readonly progBytes = new Uint8Array(this.progMem.buffer);
@@ -34,7 +36,14 @@ export class CPU implements ICPU {
   pc = 0;
   cycles = 0;
 
-  constructor(public progMem: Uint16Array) {}
+  constructor(public progMem: Uint16Array, private sramBytes = 8192) {
+    this.reset();
+  }
+
+  reset() {
+    this.data.fill(0);
+    this.SP = this.data.length - 1;
+  }
 
   readData(addr: number) {
     return this.data[addr];