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From: "Gaëtan Carlier" <gcembed@gmail.com>
To: Jonathan Cameron <jic23@jic23.retrosnub.co.uk>
Cc: linux-iio@vger.kernel.org
Subject: Re: Buffer size for iio_push_to_buffers_with_timestamp()
Date: Sun, 12 May 2019 15:53:44 +0200	[thread overview]
Message-ID: <7d412499-a8d3-6074-6566-e4f99bd77f45@gmail.com> (raw)
In-Reply-To: <20190511094824.5f57f6fa@archlinux>

Hi Jonathan,

On 5/11/19 10:48 AM, Jonathan Cameron wrote:
> On Thu, 9 May 2019 12:54:34 +0200
> Gaëtan Carlier <gcembed@gmail.com> wrote:
> 
>> Dear,
>>
>> I have a question about the function iio_push_to_buffers_with_timestamp().
>>
>> How kernel knows the size of the buffer ? Should the buffer always be 128 bits (with last 64 bits for timestamp) ?
> Hi Gaëtan,
> 
> All fields in IIO buffers are 'naturally' aligned and must be power of 2 size
> (8, 16, 32, 64)
> 
> This function is a bit 'odd' in that it needs a buffer that has space to insert
> the 64 bit aligned, 64 bit timestamp.
> 
> So if your devices other channels fit in 64 bits then your conclusion is
> correct.  If you have more channels then it may well be that the buffer
> is already greater than 64 bits long before leaving space for the timestamp
> and hence your buffer may need to be 192, 256 etc..
> 
Thank you for your reply.

> Hope that answers your question,
So, I still have a question. How IIO functions knows how many space is available because it handles "void *". Is the size of allocated buffer stored somewhere ?

> 
> Jonathan
> 
>>
>> Best regards,
>> Gaëtan.
> 

Best regards,
Gaëtan.

  reply	other threads:[~2019-05-12 13:53 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-09 10:54 Buffer size for iio_push_to_buffers_with_timestamp() Gaëtan Carlier
2019-05-11  8:48 ` Jonathan Cameron
2019-05-12 13:53   ` Gaëtan Carlier [this message]
2019-05-18  8:54     ` Jonathan Cameron

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