Added de-emphasis filter functions and speaker protection.

[aic34-eq] / kernel-2.6.28 / Documentation / sound / alsa / soc / tlv320aic3x.txt

diff --git a/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt b/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt
index ec748f2..71dd24d 100644 (file)
--- a/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt
+++ b/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt
@@ -12,48 +12,67 @@ The rest of the controls are for the IIR filter:
 
 1- A control for setting the bass/treble gain, which sets the filter's
    coefficients to certain precalculated values.
-2- A control for 'off' / 'on' / 'external control'. 'On' means the 
-   bass/treble gain is used, while 'external control' means the 
+2- A control for 'off' / 'Bass/Treble' / 'Custom'. 'Bass/Treble' means
+   the bass/treble gain controls are used, while 'custom' means the 
    coefficients have been set through the hwdep device (see below).
+Note: bass/treble controls are not yet implemented
 
+Filters
+--------
+Note: Setting a filter's coeffs automatically turns it off, it needs to
+be turned on explicitly.
 
+The De-emphasis filter can only be controlled on the machine driver level.
+For example for the n900 (rx51.c) it is used as highpass filter for
+speaker protection. See tlv320aic3x.h, aic3x_deemph_set_* for details.
 
 The IIR Filter consists of 2 cascaded biquads. The formula is:
  /                                \  /                                \
 |    (N0 + 2*N1*z^-1 + N2*z^-2)    ||    (N3 + 2*N4*z^-1 + N5*z^-2)    |
 |  ------------------------------  ||  ------------------------------  |
- \ (32768 - 2*D1*z^-1 - D2*z^-2)  /  \ (32768 - 2*D4*z^-1 - D5*z^-2)  /
+|  (32768 - 2*D1*z^-1 - D2*z^-2)   ||   (32768 - 2*D4*z^-1 - D5*z^-2)  |
+ \                                /  \                                /
 
 The filter can be controlled through an alsa hwdep device, via 
-libalsa. A short example follows, note that the data struct must be
-passed *EXACTLY* as shown:
+libasound. A short example follows, note that the data struct must be
+passed *EXACTLY* as shown. Remember to link against libasound:
+gcc myapp.c -lasound -o myapp
 
+-------------------------------EXAMPLE----------------------------------
 #include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <alsa/asoundlib.h>
 #include <alsa/hwdep.h>
 
-struct _iirfilter_data {
+struct iirfilter_data {
     int16_t N0, N1, N2, D1, D2;
     int16_t N3, N4, N5, D4, D5;
-} iirfilter_data;
+};
 
-/* Initialize */
-snd_hwdep *hwdep;
+int main() {
+    int ret;
+    snd_hwdep_t *hwdep;
+    struct iirfilter_data data = {
+           .N0 = 27619, .N1 = -27034, .N2 = 26461, .D1 = 32131, .D2 = -31506,
+        .N3 = 27619, .N4 = -27034, .N5 = 26461, .D4 = 32131, .D5 = -31506
+    };
 
-snd_hwdep_open(&hwdep, "IIR Filter", "w");
+/* Initialize */
+    ret = snd_hwdep_open(&hwdep, "hw:0,0", SND_HWDEP_OPEN_DUPLEX);
+    if(ret != 0) exit(1);
 
 /* To write: */
-iirfilter_data = {
-       .N0 = 27619, .N1 = -27034, .N2 = 26461, .D1 = 32131, .D2 = -31506,
-    .N3 = 27619, .N4 = -27034, .N5 = 26461, .D4 = 32131, .D5 = -31506
-};
-
-snd_hwdep_write(hwdep, (void*)iirfilter_data, sizeof(iirfilter_data));
+    snd_hwdep_write(hwdep, (void*)&data, sizeof(data));
 
 /* To read: */
-snd_hwdep_read(hwdep, (void*)iirfilter_data, sizeof(iirfilter_data));
+    snd_hwdep_read(hwdep, (void*)&data, sizeof(data));
 
 /* To enable/disable filtering: */
-int arg = 1; /* 1 = enable, 0 = disable */
-snd_hwdep_ioctl(hwdep, 1, &arg);
-
+    int arg = 1; /* 1 = enable, 0 = disable */
+    snd_hwdep_ioctl(hwdep, 1, &arg);
+    return 0;
+}
+------------------------------------------------------------------------