3 files changed, 35 insertions, 5 deletions
diff --git a/src/cpu/cpu.ts b/src/cpu/cpu.ts
index 2675d1d..fe3bf63 100644
--- a/src/cpu/cpu.ts
+++ b/src/cpu/cpu.ts
@@ -141,9 +141,10 @@ export class CPU {
   }
 
   updateInterruptEnable(interrupt: AVRInterruptConfig, registerValue: u8) {
-    const { enableMask, flagRegister, flagMask } = interrupt;
+    const { enableMask, flagRegister, flagMask, inverseFlag } = interrupt;
     if (registerValue & enableMask) {
-      if (this.data[flagRegister] & flagMask) {
+      const bitSet = this.data[flagRegister] & flagMask;
+      if (inverseFlag ? !bitSet : bitSet) {
         this.queueInterrupt(interrupt);
       }
     } else {
diff --git a/src/peripherals/eeprom.spec.ts b/src/peripherals/eeprom.spec.ts
index 8f08e47..a90116f 100644
--- a/src/peripherals/eeprom.spec.ts
+++ b/src/peripherals/eeprom.spec.ts
@@ -99,7 +99,30 @@ describe('EEPROM', () => {
       cpu.writeData(EEDR, 0x55);
       cpu.writeData(EEARL, 15);
       cpu.writeData(EEARH, 0);
-      cpu.writeData(EECR, EEMPE | EERIE);
+      cpu.writeData(EECR, EEMPE);
+      cpu.data[SREG] = 0x80; // SREG: I-------
+      cpu.writeData(EECR, EEPE | EERIE);
+      cpu.cycles += 1000;
+      cpu.tick();
+      // At this point, write shouldn't be complete yet
+      expect(cpu.data[EECR] & EEPE).toEqual(EEPE);
+      expect(cpu.pc).toEqual(0);
+      cpu.cycles += 10000000;
+      // And now, 10 million cycles later, it should.
+      cpu.tick();
+      expect(eepromBackend.memory[15]).toEqual(0x55);
+      expect(cpu.data[EECR] & EEPE).toEqual(0);
+      expect(cpu.pc).toEqual(0x2c); // EEPROM Ready interrupt
+    });
+
+    it('should clear the fire an interrupt when there is a pending interrupt and the interrupt flag is enabled (issue #110)', () => {
+      const cpu = new CPU(new Uint16Array(0x1000));
+      const eepromBackend = new EEPROMMemoryBackend(1024);
+      new AVREEPROM(cpu, eepromBackend);
+      cpu.writeData(EEDR, 0x55);
+      cpu.writeData(EEARL, 15);
+      cpu.writeData(EEARH, 0);
+      cpu.writeData(EECR, EEMPE);
       cpu.data[SREG] = 0x80; // SREG: I-------
       cpu.writeData(EECR, EEPE);
       cpu.cycles += 1000;
@@ -112,6 +135,8 @@ describe('EEPROM', () => {
       cpu.tick();
       expect(eepromBackend.memory[15]).toEqual(0x55);
       expect(cpu.data[EECR] & EEPE).toEqual(0);
+      cpu.writeData(EECR, EERIE);
+      cpu.tick();
       expect(cpu.pc).toEqual(0x2c); // EEPROM Ready interrupt
     });
 
diff --git a/src/peripherals/eeprom.ts b/src/peripherals/eeprom.ts
index 8056847..045ffe8 100644
--- a/src/peripherals/eeprom.ts
+++ b/src/peripherals/eeprom.ts
@@ -58,6 +58,7 @@ const EEMPE = 1 << 2;
 const EERIE = 1 << 3;
 const EEPM0 = 1 << 4;
 const EEPM1 = 1 << 5;
+const EECR_WRITE_MASK = EEPE | EEMPE | EERIE | EEPM0 | EEPM1;
 
 export class AVREEPROM {
   /**
@@ -91,6 +92,9 @@ export class AVREEPROM {
 
       const addr = (this.cpu.data[EEARH] << 8) | this.cpu.data[EEARL];
 
+      this.cpu.data[EECR] = (this.cpu.data[EECR] & ~EECR_WRITE_MASK) | (eecr & EECR_WRITE_MASK);
+      this.cpu.updateInterruptEnable(this.EER, eecr);
+
       if (eecr & EERE) {
         this.cpu.clearInterrupt(this.EER);
       }
@@ -116,6 +120,7 @@ export class AVREEPROM {
       if (eecr & EEPE) {
         //  If EEMPE is zero, setting EEPE will have no effect.
         if (this.cpu.cycles >= this.writeEnabledCycles) {
+          this.cpu.data[EECR] &= ~EEPE;
           return true;
         }
         // Check for write-in-progress
@@ -147,10 +152,9 @@ export class AVREEPROM {
         // When EEPE has been set, the CPU is halted for two cycles before the
         // next instruction is executed.
         this.cpu.cycles += 2;
-        return true;
       }
 
-      return false;
+      return true;
     };
   }
 }