Re: [Alsa-user] Get SPDIF-in sample rate

2017-07-18 Thread Denis Shulyaka
2017-07-18 8:47 GMT+02:00 Clemens Ladisch :

> In general, SPDIF inputs do not resample, and if you try to record with
> the wrong sample rate, the result has the original sample rate and is
> just labelled wrong.
>

That is a good news, but I would still prefer to know the sample rate
because if I want to output it, I would need to open the output device with
the correct sample rate, or I will still have a resampling.

> Does ALSA provide any general interface for the userspace applications
> > that indicates the SPDIF source sample rate?
>
> Yes, but the USB audio driver does not implement it because the USB
> audio specification does not define such an interface between the driver
> and the device.
>

What could I use if I had a non-USB sound card with SPDIF-in?


> At the moment, you have to write the code yourself.  But if you've
> tested it, we would be interested in integrating it into the kernel
> driver.
>

The below program outputs the current SPDIF-In sample rate of my card. The
only problem with it is that my sense of perfection hurts when I'm working
around the driver like that. All device-specific parts should be in kernel.

[root@speaker cm106spdif]# gcc cm106spdif.c -l hidapi-libusb
[root@speaker cm106spdif]# ./a.out
44.1K
[root@speaker cm106spdif]# cat cm106spdif.c
#include 
#include 
#include 
#include 
#include 

int cm106_read(hid_device *handle, char reg, uint16_t *data)
{
unsigned char buf[5] = {0x00,// report id for hidapi
0x30,// 0x20 to write, 0x30 to read
0x00,// DATAL
0x00,// DATAH
reg};// Register address

if (hid_write(handle, buf, 5) != 5)
return -1;

if (hid_read(handle, buf, 5) != 3)
return -2;

if (buf[0] & 0xe0 != 0x20)// No register data in the input report
return -3;

*data = (((uint16_t)buf[2]) << 8) + buf[1];
return 0;
}

int cm106_write(hid_device *handle, char reg, uint16_t data)
{
unsigned char buf[5] = {0x00,// report id for hidapi
0x20,// 0x20 to write, 0x30 to read
data & 0xff,// DATAL
(data >> 8),// DATAH
reg};// Register address

if (hid_write(handle, buf, 5) != 5)
return -1;

return 0;
}

int main(void)
{
hid_device *handle;
uint16_t data = 0;
unsigned char SPDFI_FREQ;

if ( !(handle = hid_open(0xd8c, 0x102, NULL)) )
err(1, "hid_open: %ls", hid_error(handle));

if (cm106_read(handle, 3, ) < 0)
err(2, "read: %ls", hid_error(handle));

//printf("data=%04X\n", data);

SPDFI_FREQ = (data & 0x0180) >> 7;

switch(SPDFI_FREQ)
{
case 0:
printf("44.1K\n");
break;

case 2:
printf("48K\n");
break;

case 3:
printf("32K\n");
break;
default:
printf("reserved\n");
}

hid_close(handle);
hid_exit();
return 0;
}


Best regards,
Denis Shulyaka
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Re: [Alsa-user] Get SPDIF-in sample rate

2017-07-18 Thread Clemens Ladisch
Denis Shulyaka wrote:
> I have a CM106-based usb sound card (0d8c:0102) with SPDIF-In. My aim
> is to decode the compressed audio formats that may come from this
> source. And the first task for this is to get the original sample rate
> of the source to avoid any resampling.

In general, SPDIF inputs do not resample, and if you try to record with
the wrong sample rate, the result has the original sample rate and is
just labelled wrong.

And in practice, everybody uses 48 kHz.

> According to the CM106 datasheet, one can read the SPDIF-In sample
> rate from SPDFI_FREQ bits (8~7 of register 03).
> What is the correct way to do so? Can ALSA read those register bits?

In theory, this would be possible.

> Does ALSA provide any general interface for the userspace applications
> that indicates the SPDIF source sample rate?

Yes, but the USB audio driver does not implement it because the USB
audio specification does not define such an interface between the driver
and the device.

> Should I attempt to communicate with the hardware with libusb, or can
> I do it with ALSA only?

At the moment, you have to write the code yourself.  But if you've
tested it, we would be interested in integrating it into the kernel
driver.


Regards,
Clemens

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