Merge pull request #326 from widdly/master

fix slave i2s output on teensy 4

output_i2s.cpp

@@ -475,6 +475,7 @@ void AudioOutputI2Sslave::begin(void)
 	dma.TCD->DLASTSGA = 0;
 	dma.TCD->BITER_ELINKNO = sizeof(i2s_tx_buffer) / 2;
 	dma.TCD->DADDR = (void *)((uint32_t)&I2S1_TDR0 + 2);
+	dma.TCD->CSR = DMA_TCD_CSR_INTHALF | DMA_TCD_CSR_INTMAJOR;
 	dma.triggerAtHardwareEvent(DMAMUX_SOURCE_SAI1_TX);
 	dma.enable();