2 files changed, 43 insertions, 0 deletions
diff --git a/src/peripherals/gpio.spec.ts b/src/peripherals/gpio.spec.ts
index f3b1a0f..1dfaf7d 100644
--- a/src/peripherals/gpio.spec.ts
+++ b/src/peripherals/gpio.spec.ts
@@ -93,4 +93,27 @@ describe('GPIO', () => {
       expect(listener).toHaveBeenCalled();
     });
   });
+
+  describe('setPin', () => {
+    it('should set the value of the given pin', () => {
+      const cpu = new CPU(new Uint16Array(1024));
+      const port = new AVRIOPort(cpu, portBConfig);
+      cpu.writeData(0x24, 0); // DDRB <- 0
+      port.setPin(4, true);
+      expect(cpu.data[0x23]).toEqual(0x10);
+      port.setPin(4, false);
+      expect(cpu.data[0x23]).toEqual(0x0);
+    });
+
+    it('should only update PIN register when pin in Input mode', () => {
+      const cpu = new CPU(new Uint16Array(1024));
+      const port = new AVRIOPort(cpu, portBConfig);
+      cpu.writeData(0x24, 0x10); // DDRB <- 0x10
+      cpu.writeData(0x25, 0x0); // PORTB <- 0x0
+      port.setPin(4, true);
+      expect(cpu.data[0x23]).toEqual(0x0);
+      cpu.writeData(0x24, 0x0); // DDRB <- 0x0
+      expect(cpu.data[0x23]).toEqual(0x10);
+    });
+  });
 });
diff --git a/src/peripherals/gpio.ts b/src/peripherals/gpio.ts
index ba3217b..e3c8eaa 100644
--- a/src/peripherals/gpio.ts
+++ b/src/peripherals/gpio.ts
@@ -92,10 +92,12 @@ export enum PinState {
 
 export class AVRIOPort {
   private listeners: GPIOListener[] = [];
+  private pinValue: u8 = 0;
 
   constructor(private cpu: CPU, private portConfig: AVRPortConfig) {
     cpu.writeHooks[portConfig.DDR] = (value, oldValue) => {
       const portValue = cpu.data[portConfig.PORT];
+      this.updatePinRegister(portValue, value);
       this.writeGpio(value & portValue, oldValue & oldValue);
     };
     cpu.writeHooks[portConfig.PORT] = (value: u8, oldValue: u8) => {
@@ -103,6 +105,7 @@ export class AVRIOPort {
       cpu.data[portConfig.PORT] = value;
       value &= ddrMask;
       cpu.data[portConfig.PIN] = (cpu.data[portConfig.PIN] & ~ddrMask) | value;
+      this.updatePinRegister(value, ddrMask);
       this.writeGpio(value, oldValue & ddrMask);
       return true;
     };
@@ -145,6 +148,23 @@ export class AVRIOPort {
     }
   }
 
+  /**
+   * Sets the input value for the given pin. This is the value that
+   * will be returned when reading from the PIN register.
+   */
+  setPin(index: number, value: boolean) {
+    const bitMask = 1 << index;
+    this.pinValue &= ~bitMask;
+    if (value) {
+      this.pinValue |= bitMask;
+    }
+    this.updatePinRegister(this.cpu.data[this.portConfig.PORT], this.cpu.data[this.portConfig.DDR]);
+  }
+
+  private updatePinRegister(port: u8, ddr: u8) {
+    this.cpu.data[this.portConfig.PIN] = (this.pinValue & ~ddr) | (port & ddr);
+  }
+
   private writeGpio(value: u8, oldValue: u8) {
     for (const listener of this.listeners) {
       listener(value, oldValue);