Merge pull request #51 from xhuw/feature/readme-note-on-clocks

Update with some fixes for 3B mclk phase issue

CHANGELOG.md

@@ -1,5 +1,9 @@
 # VocalFusion Raspberry Pi Setup Change Log
 
+## 5.4.0
+
+  * Fix and document MCLK phase issue found on raspberry pi 3b
+
 ## 5.3.0
 
   * Fix setup_dac.py script for XVF3615

README.md

@@ -104,3 +104,20 @@ For XVF3510-UA and XVF361x-UA devices these actions will be done as well:
    Wait for the script to complete the installation. This can take several minutes.
 
 5. Reboot the Raspberry Pi.
+
+## Important note on clocks
+
+The I2S/PCM driver that is provided with rasbian does not support an MCLK output. However the 
+driver does have full ability to set the BCLK and LRCLK correctly for a given sample rate. As 
+the driver does not know about the MCLK it is likely to choose dividers for the clocks generators
+which are not phase locked to the MCLK. The script in this repo gets around this problem by 
+configuring the i2s driver to a certain frequency and then overriding the clock registers to force
+a phase locked frequency.
+
+This will work until a different sample rate is chosen by an application, then the I2S driver will
+write it's own value to the clocks and the MCLK will no longer be phase locked. To solve this problem
+the following steps must be taken before connecting an XVF device with a different sample rate:
+
+1. Take a short recording at the new sample rate: `arecord -c2 -fS32_LE -r{sample_rate} -s1 -Dhw:sndrpisimplecar`
+2. For 48kHz `./resources/clk_dac_setup/setup_blk`, for 16kHz `./resources/clk_dac_setup/setup_blk`
+

setup.sh

@@ -225,6 +225,15 @@ if [[ -n "$I2S_MODE" ]]; then
   echo "# Run Alsa at startup so that alsamixer configures" >> $i2s_driver_script	
   echo "arecord -d 1 > /dev/null 2>&1"                      >> $i2s_driver_script	
   echo "aplay dummy > /dev/null 2>&1"                       >> $i2s_driver_script
+
+  if [[ "$I2S_MODE" = "master" ]]; then
+    echo "# Preconfigure i2s clocks to 48kHz"               >> $i2s_driver_script
+    # wait a bit as it doesn't work otherwise, this is probably caused
+    # by the same process that is deleting .asoundrc
+    echo "sleep 15"                                         >> $i2s_driver_script
+    echo "arecord -Dhw:sndrpisimplecar,0 -c2 -fS32_LE -r48000 -s1 /dev/null" >> $i2s_driver_script
+    echo "sudo $RPI_SETUP_DIR/resources/clk_dac_setup/setup_bclk" >> $i2s_driver_script
+  fi
 fi
 
 if [[ -n "$DAC_SETUP" ]]; then