feat(twi): proper interrupt support #10

2 files changed, 20 insertions, 5 deletions

diff --git a/src/twi.spec.ts b/src/twi.spec.ts
index de7ceb8..369f22a 100644
--- a/src/twi.spec.ts
+++ b/src/twi.spec.ts
@@ -46,6 +46,17 @@ describe('TWI', () => {
     expect(twi.sclFrequency).toEqual(400000);
   });
 
+  it('should trigger data an interrupt if TWINT is set', () => {
+    const cpu = new CPU(new Uint16Array(1024));
+    const twi = new AVRTWI(cpu, twiConfig, FREQ_16MHZ);
+    cpu.writeData(0xbc, 0x81); // TWCR <- TWINT | TWIE
+    cpu.data[95] = 0x80; // SREG: I-------
+    twi.tick();
+    expect(cpu.pc).toEqual(0x30); // 2-wire Serial Interface Vector
+    expect(cpu.cycles).toEqual(2);
+    expect(cpu.data[0xbc] & 0x80).toEqual(0); // UCSR0A should clear TWINT
+  });
+
   describe('Master mode', () => {
     it('should call the startEvent handler when TWSTA bit is written 1', () => {
       const cpu = new CPU(new Uint16Array(1024));
diff --git a/src/twi.ts b/src/twi.ts
index 027061f..fd0645b 100644
--- a/src/twi.ts
+++ b/src/twi.ts
@@ -1,6 +1,6 @@
-import { u8 } from './types';
 import { CPU } from './cpu';
 import { avrInterrupt } from './interrupt';
+import { u8 } from './types';
 
 export interface TWIEventHandler {
   start(repeated: boolean): void;
@@ -133,6 +133,13 @@ export class AVRTWI {
       this.nextTick();
       this.nextTick = null;
     }
+    if (this.cpu.interruptsEnabled) {
+      const { TWCR, twiInterrupt } = this.config;
+      if (this.cpu.data[TWCR] & TWCR_TWIE && this.cpu.data[TWCR] & TWCR_TWINT) {
+        avrInterrupt(this.cpu, twiInterrupt);
+        this.cpu.data[TWCR] &= ~TWCR_TWINT;
+      }
+    }
   }
 
   get prescaler() {
@@ -186,11 +193,8 @@ export class AVRTWI {
   }
 
   private updateStatus(value: u8) {
-    const { TWCR, TWSR, twiInterrupt } = this.config;
+    const { TWCR, TWSR } = this.config;
     this.cpu.data[TWSR] = (this.cpu.data[TWSR] & ~TWSR_TWS_MASK) | value;
     this.cpu.data[TWCR] |= TWCR_TWINT;
-    if (this.cpu.interruptsEnabled && this.cpu.data[TWCR] & TWCR_TWIE) {
-      avrInterrupt(this.cpu, twiInterrupt);
-    }
   }
 }