本博客转载自台湾朋友的文章：http://3sec.kilab.tw/?p=260
在處理音訊相關的問題時，我通常會找個方法來讀寫codec中register的值。幸好linux上也有這樣的工具 – i2c tools。先到lm-sensors下載soure code，然後cross compile成arm的執行檔，就可以放到板子來試試看了。
i2c-tools中含有四個執行檔
i2cdetect – 用來列舉I2C bus和上面所有的裝置
i2cdump – 顯示裝置上所有register的值
i2cget – 讀取裝置上某個register的值
i2cset – 寫入裝置上某個register
以下是我用beagleboard得到的結果
root@android:/temp # ./i2cdetect -l
i2c-1 i2c OMAP I2C adapter I2C adapter
i2c-2 i2c OMAP I2C adapter I2C adapter
i2c-3 i2c OMAP I2C adapter I2C adapter
原來beagleboad上有三組I2C bus。
i2cdetect也可以用來看bus上有那些裝置
root@android:/temp # ./i2cdetect -y -r 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: – – – – – – – – – – – – –
10: – – – – – – – – – – – – – – – –
20: – – – – – – – – – – – – – – – –
30: – – – – – – – – – – – – – – – –
40: – – – – – – – – UU UU UU UU – – – –
50: – – – – – – – – – – – – – – – –
60: – – – – – – – – – – – – – – – –
70: – – – – – – – –
這表示bus上有四備裝置，位址分別是0×48, 0×49, 0x4a, 0x4b。
我們要找的是codec，beagleboard上的codec是TI的TPS65950，從technical reference manual可以得知codec在I2C上的位址是0×49。
然後用i2cdump來看codec中所有register的值
[
root@android:/temp # ./i2cdump -f -y 1 0x49
No size specified (using byte-data access)
0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
00: 00 00 00 00 00 00 00 00 00 00 0f 0f 0f 0f 00 00 ……….????..
10: 3f 3f 3f 3f 25 00 00 00 00 32 32 32 32 00 00 55 ????%….2222..U
20: 00 00 00 00 00 00 00 00 00 00 00 05 00 00 00 00 ………..?….
30: 13 00 00 00 00 79 11 00 00 00 06 00 44 69 02 00 ?….y?…?.Di?.
40: 00 00 00 00 32 00 00 00 00 00 00 00 00 00 00 1b ….2……….?
50: 00 00 03 f0 05 00 00 00 1a 1a 00 e1 93 00 00 00 ..???…??.??…
60: 14 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ?……………
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 …………….
80: 00 00 00 00 00 2f 00 09 10 ff ff ff ff ff ff ff …../.??…….
90: ff 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 ……..?…….
a0: 00 00 00 00 00 00 00 00 00 00 04 18 50 01 44 05 ……….??P?D?
b0: 00 00 00 00 fe ff 03 00 00 00 ff ff 03 00 00 00 ….?.?…..?…
c0: 03 00 00 00 00 04 00 00 00 00 00 00 00 00 00 00 ?….?……….
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 …………….
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 …………….
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 …………….
再來我用i2cset來改變headset gain看看會不會改變播放的音量。先用以下的指令來播放wav檔，我是用sample rate 44.1k的檔案，其它sample rate的wav可能無法播放。
root@android:/temp # ./tinymix 13 1
root@android:/temp # ./tinymix 45 1
root@android:/temp # ./tinymix 48 1
root@android:/temp # ./tinyplay 440.wav
Playing sample: 2 ch, 44100 hz, 16 bit
headset gain的register的位址是0×23，在播放的過程中打開另一個adb shell，用i2cset來增加gain
root@android:/temp # ./i2cset -f -y 1 0x49 0x23 5
音量果然變大了!
i2cget的用法類似i2cget，這裡就不多做說明了。
