From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Flax Subject: Re: [PATCH 2/2] ASoc: wm8731: add normal mode with 12MHz XTAL Date: Sun, 12 Jun 2016 13:22:26 +1000 Message-ID: <575CD572.2040700@flatmax.org> References: <1465517516-1917-1-git-send-email-flatmax@flatmax.org> <1465517516-1917-2-git-send-email-flatmax@flatmax.org> <575BD6F2.70600@flatmax.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from nskntmtas03p.mx.bigpond.com (nskntmtas03p.mx.bigpond.com [61.9.168.143]) by alsa0.perex.cz (Postfix) with ESMTP id 996B22604EB for ; Sun, 12 Jun 2016 05:22:32 +0200 (CEST) In-Reply-To: <575BD6F2.70600@flatmax.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: broonie@kernel.org, alsa-devel@alsa-project.org, patches@opensource.wolfsonmicro.com, ckeepax@opensource.wolfsonmicro.com List-Id: alsa-devel@alsa-project.org It appears that my logic here is flawed. From what I can tell, it isn't possible to get a suitable bit clock out of the codec when using a 12 MHz crystal. For that reason, in my hardware I will change crystals from 12 MHz. I just want to check ... are there any versions of this codec which output the bit clock when in USB mode on the BCLK pin ? thanks Matt On 11/06/16 19:16, Matt Flax wrote: > I have realised that this second patch may not be necessary. It is > also likely that it will skew the actual sample rate. > > Charles, can you please advise me on the following... > > I notice that I can probably get the correct sample rates by spoofing > the crystal frequencies in my machine driver. For example ... > The ratio between the USB and Normal mode fs multipliers with BOSR=0 is : > 250/256 = 0.97656 > Similarly, I can match this with the following crystal frequency ratio > (crystal f in MHz) : > 12/12.288 = 0.97656 > By induction, I assume that I can spoof a 12.288 clock with BOSR=0 for > sample rate = 48kHz, 96 kHz when using a 12 MHz crystal. > > Again, I can match ratios between the following crystal frequecies (in > MHz) : > 12/16.9344 = 0.70862 > With BOSR = 1, I assume that can get 44.1 kHz and 88.2 kHz because the > fs ratio between normal and usb mode is : > 272/384 = 0.70833 > > Now these two ratios are skew by 0.41% which is equvalent to the skew > in 12 MHz USB mode clocks of 44.1kHz to 44.118kHz as reported in the > wm8731 datasheet. > > Can you advise me whether my idea of spoofing clocks in the machine > driver is perhaps a better way of acquiring the correct sample rates, > rather then this patch ? > > thanks > Matt > > On 10/06/16 10:11, Matt Flax wrote: >> This patch allows a machine to set normal mode when using a >> 12 MHz crystal. In USB_MODE the 12 MHz crystal signal is output on >> the BCLK pin. In NORMAL_MODE the bit clock is output on the BCLK pin. >> The previously ignored direction variable input to the >> wm8731_set_dai_sysclk function is used to indicate whether crystal >> or bit clock is output on the BCLK codec pin. >> I have ensured that this does not effect the db1200.c machine driver >> (the only other driver to use a 12 MHz crystal in USB_MODE). It also >> does not effect the other machine drivers which use the wm8731 codec >> as they don't use USB_MODE nor 12 MHz crystals. >> >> When driving the wm8731 in normal mode with a 12 MHz crystal, the >> DSP filters are expected to be effected. If the filters are activated >> then it is expected that the filter cut offs are shifted by 2.3% at >> 250 fs and 29.1% at 272 fs. The assumption is that the filters are >> linear, which implies a linear shift in rate scaling effects the >> filter cut off frequencies linearly. If the filters are not active, >> there will be no effects. >> >> Signed-off-by: Matt Flax >> --- >> sound/soc/codecs/wm8731.c | 14 ++++++++++++-- >> 1 file changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/sound/soc/codecs/wm8731.c b/sound/soc/codecs/wm8731.c >> index d18261a..ec98d5a 100644 >> --- a/sound/soc/codecs/wm8731.c >> +++ b/sound/soc/codecs/wm8731.c >> @@ -5,6 +5,7 @@ >> * Copyright 2006-12 Wolfson Microelectronics, plc >> * >> * Author: Richard Purdie >> + * Author: Matt Flax 12Mhz XTAL normal mode >> and 32bit mode. >> * >> * Based on wm8753.c by Liam Girdwood >> * >> @@ -53,6 +54,7 @@ struct wm8731_priv { >> int sysclk_type; >> int playback_fs; >> bool deemph; >> + bool bclk_12_mhz; >> struct mutex lock; >> }; >> @@ -341,8 +343,11 @@ static int wm8731_hw_params(struct >> snd_pcm_substream *substream, >> struct wm8731_priv *wm8731 = snd_soc_codec_get_drvdata(codec); >> u16 iface = snd_soc_read(codec, WM8731_IFACE) & 0xfff3; >> int i = get_coeff(wm8731->sysclk, params_rate(params)); >> - u16 srate = (coeff_div[i].sr << 2) | >> - (coeff_div[i].bosr << 1) | coeff_div[i].usb; >> + u16 srate = (coeff_div[i].sr << 2) | (coeff_div[i].bosr << 1); >> + >> + /* this determines whether to output bit or crystal clk */ >> + if (wm8731->bclk_12_mhz) >> + srate |= coeff_div[i].usb; >> wm8731->playback_fs = params_rate(params); >> @@ -420,6 +425,11 @@ static int wm8731_set_dai_sysclk(struct >> snd_soc_dai *codec_dai, >> wm8731->sysclk = freq; >> + if (dir == SND_SOC_CLOCK_IN) /* output the 12 MHz clock */ >> + wm8731->bclk_12_mhz = 1; >> + else /* SND_SOC_CLOCK_OUT, output the bit clock */ >> + wm8731->bclk_12_mhz = 0; >> + >> snd_soc_dapm_sync(dapm); >> return 0; >