Update: doc about limit for doing capture & playback the same time

Author: turmary

README.md

@@ -193,7 +193,7 @@ plughw:CARD=seeed8micvoicec,DEV=0
 [![](https://user-images.githubusercontent.com/3901856/37194106-a0ccebce-23a7-11e8-88c5-ec611e44ec49.png)]()
 
 In contrast to 6-Mics Circular Array Kit for Raspberry Pi,
-the difference is only first 4 input channels are valid capturing data.
+the difference is only first 4 input channels are valid capture data.
 
 ### Usage:
 ```bash
@@ -217,9 +217,15 @@ arecord -Dac108 -f S32_LE -r 16000 -c 8 a.wav
 #It will play sound file a.wav on AC101
 aplay -D ac101 a.wav
 #Do not use -D plughw:1,0 directly except your wave file is single channel only.
+
+#Doing capture && playback the same time
+arecord -D hw:1,0 -f S32_LE -r 16000 -c 8 toberecord.wav &
+#mono_toplay.wav is a mono channel wave file to play
+aplay -D plughw:1,0 -r 16000 mono_toplay.wav
 ```
-**Note: for developer using 6-Mics Circular Array Kit(or 4-Mics Linear Array Kit) doing capturing & playback the same time,
-capturing must be start first, or else the capturing channels will miss order.**
+**Note: Limit for developer using 6-Mics Circular Array Kit(or 4-Mics Linear Array Kit) doing capture & playback the same time:  
+1. capture must be start first, or else the capture channels will miss order randomly.  
+2. playback output channels must fill with 8 same channels data or 4 same stero channels dat, or else the speaker or headphone will output nothing randomly.**
 
 ### Coherence
 

ac101.c

@@ -626,6 +626,9 @@ static int ac101_set_pll(struct snd_soc_dai *codec_dai, int pll_id, int source,
 
 	AC101_DBG("%s, line:%d, pll_id:%d\n", __func__, __LINE__, pll_id);
 
+	/* clear volatile reserved bits*/
+	ac101_update_bits(codec, SYSCLK_CTRL, 0xFF & ~(0x1 << SYSCLK_ENA), 0x0);
+
 	/* select aif1 clk srouce from mclk1 */
 	ac101_update_bits(codec, SYSCLK_CTRL, (0x3<<AIF1CLK_SRC), (0x0<<AIF1CLK_SRC));
 	/* disable pll */

ac108.c

@@ -191,7 +191,7 @@ int ac10x_update_bits(u8 reg, u8 mask, u8 val, struct regmap* i2cm) {
 	int r;
 
 	if ((r = regmap_update_bits(i2cm, reg, mask, val)) < 0) {
-		pr_err("ac10x_update error->[REG-0x%02x,val-0x%02x]\n", reg, val);
+		pr_err("%s() error->[REG-0x%02x,val-0x%02x]\n", __func__, reg, val);
 	}
 	return r;
 }
@@ -694,8 +694,6 @@ static int ac108_hw_params(struct snd_pcm_substream *substream, struct snd_pcm_h
 		return -EINVAL;
 	}
 
-	dev_dbg(dai->dev, "params rate: %d\n", params_rate(params));
-
 	for (i = 0; i < ARRAY_SIZE(ac108_sample_rate); i++) {
 		if (ac108_sample_rate[i].real_val == params_rate(params) / (ac10x->data_protocol + 1UL)) {
 			rate = i;