Hi Mark,
+static u16 wm8940_reg_defaults[] = {
- [WM8940_SOFTRESET] = 0x8940,
- [WM8940_POWER1] = 0x0000,
I'd really rather use the more standard ASoC style here with a simple table of values. The driver relies on the fact that the register cache is fully specified for suspend and resume and having a straight table makes sure that there aren't any missing values in the cache.
Ok, though I'd place the alternate argument that it lead to rather less readable code than this sort of syntax where it readily apparent exactly what is in each register.
Sure - if you do this using an alternative syntax that'd be fine. For example, several of the other drivers use comments to provide the register names.
Yup, that's what I've moved over to.
- SOC_SINGLE("Digital Loopback Switch adc to dac", WM8940_COMPANDINGCTL,
0, 1, 0),This should be called Digital Sidetone Switch and probably ought to be a DAPM control - there's an ADC to DAC route.
I'll take your word for it!
If you switch the ADC to the DAC then you've got an audio path between them.
Got that. It was the fact it was a Sidetone Switch that I was surprised by!
- SOC_SINGLE_TLV("Speaker Playback Volume", WM8940_SPKVOL,
0, 63, 0, wm8940_spk_vol_tlv),- SOC_SINGLE("Speaker Playback Mute", WM8940_SPKVOL, 6, 1, 0),
Speaker Playback Switch; this also means that the sense of the control needs to be inverted. Look at the control in alsamixer and you'll see that it figures out that these both control the same thing and displays them as a single Speaker Playback control in the UI.
I wish, alsamixer isn't exactly playing ball with busy box for some reason I haven't chased down. Looking at this lot using amixer isn't much fun!
amixer should show you the same information - yo'll get a simple mixer control with both switch and volume capabilites.
It does indeed, but there are so many controls it is a pain to find the one you want making checking this lot rather time consuming.
I'll try and work out how to do it right before next posting! Need to lure the board side of things into a configuration where this is relevant.
If you've got a scope you can use that to generate clocks with broken audio.
Yup, fun and games to come.
- case SND_SOC_BIAS_PREPARE:
/* ensure bufioen and biasen */pwr_reg |= (1 << 2) | (1 << 3);/* set vmid to 2.5k for fast start */wm8940_write(codec, WM8940_POWER1, pwr_reg | 0x3);break;This isn't what the low resistance VMID setting is for;
I admit I didn't really understand what was going on here, so I think I cribbed it from another driver. What should the setting be? (and what is that setting for?)
Sorry, didn't finish writing that bit. You should be setting the bias for normal operation in prepare - the fast startup is only for use during initial bringup of VMID since the lower resistrance allows the capacitor used to charge more quickly.
The resistance of the VMID resistor string allows you to trade the accuracy with which the VMID reference voltage is held (and therefore audio performance) for power consumption. Since it can take time to charge the capacitors and bring VMID up to the required voltage it's desirable to maintian VMID while the system is active in order to allow rapid startup of an audio stream but doing so consumes power so the higher resistance value is provided in order to allow that consumption to be reduced. The savings involved are very small but can produce a noticable benefit in small, power sensitive devices like MP3 players.
Ah, that makes sense now.
Thanks
Jonathan