Fix PT8211 on Teensy 4.x

output_pt8211.cpp

 
 void AudioOutputPT8211::isr(void)
 {
-	int16_t *dest;
+	int16_t *dest, *dest_copy;
 	audio_block_t *blockL, *blockR;
 	uint32_t saddr, offsetL, offsetR;
 
 		// so we must fill the first half
 		dest = (int16_t *)i2s_tx_buffer;
 	}
+	dest_copy = dest;
 
 	blockL = AudioOutputPT8211::block_left_1st;
 	blockR = AudioOutputPT8211::block_right_1st;
 		return;
 	}
 
+	arm_dcache_flush_delete(dest_copy, sizeof(i2s_tx_buffer) / 2);
+
 	if (offsetL < AUDIO_BLOCK_SAMPLES) {
 		AudioOutputPT8211::block_left_offset = offsetL;
 	} else {

output_pt8211_2.cpp

 
 void AudioOutputPT8211_2::isr(void)
 {
-	int16_t *dest;
+	int16_t *dest, *dest_copy;
 	audio_block_t *blockL, *blockR;
 	uint32_t saddr, offsetL, offsetR;
 
 		// so we must fill the first half
 		dest = (int16_t *)i2s_tx_buffer;
 	}
+	dest_copy = dest;
 
 	blockL = AudioOutputPT8211_2::block_left_1st;
 	blockR = AudioOutputPT8211_2::block_right_1st;
 		return;
 	}
 
+	arm_dcache_flush_delete(dest_copy, sizeof(i2s_tx_buffer) / 2);
+
 	if (offsetL < AUDIO_BLOCK_SAMPLES) {
 		AudioOutputPT8211_2::block_left_offset = offsetL;
 	} else {