Re: FIX: soundblaster rear channels (ens1371)

[Takashi Iwai <tiwai@suse.de>]

At Fri, 17 Jan 2003 01:04:40 +0100,
Pieter Palmers wrote:
> 
> Finally I figured out how to enable the rear channel separately from the front 
> on the creative labs CT5880 (= modified ens1371 as it seems).
 
great!  thanks for your work!

> I'll describe the settings to enable this, but I'm not going to submit a 
> patch, as I have noticed that I messed up my ens1370.c too much, and I can't 
> get a clean version because CVS doesn't work. It's a minor change, so I 
> assume it can be done by the maintainers.
> 
> The whole thing is in three bits in the BASE+0x04 register (ES_REG_STATUS in 
> the driver). These bits are bit27, bit26 and bit24
> There are three modes of operation:
> 1) No rear output: bit27=bit26=bit24=0
> 2) rear output is a mirror of the main output, but controlled by the 
> 'surround' slider of the mixer. I assume the ens1371 mixes the two 'devices' 
> and sends the mix to both MAIN and SURROUND DAC. This mode is selected by 
> setting  bit27=bit24=0 and bit26=1
> 3) independant rear (surround) and front output. Using the current driver, 
> this has the strange side-effect that HW:0,0 becomes the rear output and 
> HW:0,1 becomes the front. So HW:0,0 is controlled by the 'surround' mixer 
> control, and HW:1,0 is controlled by the PCM and Master mixer
> controls.

this is because we are using DAC2 for the hw:0,0 and DAC1 for hw:0,1.
i'm not sure why it is.

Jaroslav, is there any drawback to use DAC1 as default playback?
(i know that the OSS driver uses this order, too.)


> To 
> select this mode set bit27=bit24=1 and bit26=0. It seems that bit27=1 and 
> bit24=bit26=0 is identical, but the windows driver clearly does the first, so 
> why not? It works...
> 
> front only, no rear: 		bit27=0	bit26=0	bit24=0
> rear mirrors front:		bit27=0 	bit26=1 	bit24=0
> front & rear independant:	bit27=1 	bit26=0 	bit24=1 (x?)
> 
> 
> I patched my driver by inserting the following code around line 1947:
> (I included two lines of overlap to make the location easier to find)
> =============================================
> 	outb(ensoniq->uartc = 0x00, ES_REG(ensoniq, UART_CONTROL)); 
> 	outb(0x00, ES_REG(ensoniq, UART_RES));
> 
> #ifdef CHIP1371
> 	/* enable the rear outputs
> 	This seems to work
> 	ensoniq->cssr |= (0 << 27) | (1 << 24);
> 	but the windows driver does this, so let's
> 	also do it */
> 
> 	ensoniq->cssr |= (1 << 27) | (1 << 24);
> 
> 	/*
> 	Use this for mirror mode
> 	ensoniq->cssr |= (1 << 26);*/
> #endif
> 
> 	outl(ensoniq->cssr, ES_REG(ensoniq, STATUS));
> #if defined(CONFIG_GAMEPORT) || defined(CONFIG_GAMEPORT_MODULE)
> =============================================
> 
> Maybe there is a better place to put this? I don't know... I put it in the 
> snd_ensoniq_create() function because I always want 4ch output, and I don't 
> see the use of the other modes in an ALSA enviroment.
 
it would be better to create new controls, and changing the controls
via hook in the pcm configuration.


> Regards,
> 
> Pieter
> 
> PS: I'm also developing a driver for my Maxisound ISIS, where do I look for 
> information on ALSA/linux driver developement? Does anyone have a 'template' 
> ALSA driver?

there is a tutorial,
	http://www.alsa-project.org/~iwai/writing-an-alsa-driver/index.html

the docbook source is found in alsa-kernel/Documentation/DocBook.


> Does ALSA support non-DMA audio transfer? I believe the ISIS uses this kind of 
> transfers, but I don't know for sure yet. I know it's stupid design not to 
> use DMA, but there is nothing to do about it I guess.

yes, but the implementation depends on the driver.
you can use tasklet for transferring the data e.g. via io-port
read/write.

Uros has been working on the ALSA SAM9407 driver, and IIRC, maxi ISIS
uses a similar (same?) chip.  he might be able to help the development
of this driver.


ciao,

Takashi


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