Re: [LAD] RME madi latency

From: Fokke de Jong <fokkedejong@email-addr-hidden>
Date: Sat Feb 06 2016 - 19:30:16 EET

Ok, just to be clear: I *am* able to get the expected latency using jack (around 3.5ms with a period=32 and nperiods=256).
but using my own alsa wrapper (and also using zita-alsa-pcmi) the latency is >170ms

here’s the output from hw_params:

Device: hw (type: HW)
Access types: MMAP_COMPLEX
Formats: S32_LE FLOAT_LE
Channels: 52 100 196
Sample rates: 32000 44100 48000 64000 88200 96000 176400 192000
Interrupt interval: 166-128000 us
Buffer size: 42666-256000 us

fokke

> On Feb 6, 2016, at 17:27 , Adrian Knoth <adi@drcomp.erfurt.thur.de> wrote:
>
> On Sat, Feb 06, 2016 at 04:12:39PM +0000, Fons Adriaensen wrote:
>
>>> That, helped thanks.
>>> Unfortunately I’m still getting the same huge latency as before..
>>
>> Looks like a driver problem then...
>
> Not impossible, but I fail to see how. Here is the relevant driver side:
>
> .channels_min = 1,
> .channels_max = 196,
> .buffer_bytes_max = OUTPUT_DMA_BUFFER_SIZE,
> .period_bytes_min = (32 * 4),
> .period_bytes_max = OUTPUT_DMA_BUFFER_SIZE,
> .periods_min = 2,
> .periods_max = 1024,
>
>
> and according to some doc on the internet:
>
>
> --- cut ---
> buffer_bytes_max defines the maximum buffer size in bytes. There is no
> buffer_bytes_min field, since it can be calculated from the minimum
> period size and the minimum number of periods. Meanwhile,
> period_bytes_min and define the minimum and maximum size of the period
> in bytes. periods_max and periods_min define the maximum and minimum
> number of periods in the buffer.
>
> The “period” is a term that corresponds to a fragment in the OSS world.
> The period defines the size at which a PCM interrupt is generated. This
> size strongly depends on the hardware. Generally, the smaller period
> size will give you more interrupts, that is, more controls. In the case
> of capture, this size defines the input latency. On the other hand, the
> whole buffer size defines the output latency for the playback direction.
> --- cut ---
>
> From my understanding, this allows userspace to request a buffer of
> 1ch*2periods*32samples.
>
> Fokke, do you mind running the attached program?
>
>
> Cheers
>
> --
> mail: adi@thur.de http://adi.thur.de PGP/GPG: key via keyserver
>
> <hw_params.c>

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Received on Sat Feb 6 20:15:02 2016

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