Hello,
today is my birthday and I got a shiny new multimeter as a present.
Using this new toy, I was able to squeeze a bit more information out
of my M-Audio revolution 5.1 board.
1. Input channels:
The AK5365 ADC allows to select its input from 5 different channels.
Using the multimeter I can see that at least channels 1 and 2 are
used. I think 1 is the microphone and 2 is line-in, but this is
hard to say because the lines vanish under some bulky capacitors
where it is hard to follow them.
The input select lines SEL0, SEL1, SEL2 are all pulled to ground,
which means that the input channel can be selected via register
0x01.
It would be nice if the ALSA driver would get a control to select
the input channel (it just needs to allow to set the lower three
bits of register 0x01). This should be easy.
2. PT2258 Volume Controller:
The board contains a PT2258 Volume Controller chip, which is
currently, I think, not accessible using the ALSA driver.
Originally I hoped that this chip could be used to enable the
headphone output, but it does not seem to be the case. From
following the connections I think that this chip is used to enable
analog loopback of the input lines to some output channel. At least
input 1 leads very close to the CD-input line.
All six channels are connected to something.
I could find the following direct connections:
PT2258, pin 6 (SCL) <-> VT1722, pin 59 (GPIO 7)
PT2258, pin 7 (SDA) <-> VT1722, pin 58 (GPIO 6)
The address select lines CODE1 and CODE2 seem to be pulled to GND.
So we can control this volume controller by playing with GPIO 6 and
7. This project will be a bit more challenging. One has to shift
the data to the chip bit by bit, we have to use pin 6 as the clock
(max 100kbit/s), pin 7 is only allowed to change while 6 is low and
the chip read the data while 6 is high. After every byte the chips
sends back one acknoledge bit. And the chip wants a 200ms delay
after power up. The data sheet is at
http://www.princeton.com.tw/webSite/downloadprocess/downloadfile.asp?mydownload=PT2258_2.pdf
It would be nice if the ALSA driver would allow access to these
volume controls.
All things I found out about the card, including the information
above, is collected on my web page at
http://seehuhn.de/comp/hardware/revolution
Comments are very welcome.
I hope this helps,
Jochen
--
http://seehuhn.de/
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