2017-07-18 8:47 GMT+02:00 Clemens Ladisch <clem...@ladisch.de>:
> 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 <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <err.h>
#include <hidapi/hidapi.h>
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, &data) < 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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