linux-kernel - Re: FP in kernelspace

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Message-ID: <44CCC4CA.6000208@argo.co.il>
Date:	Sun, 30 Jul 2006 17:40:10 +0300
From:	Avi Kivity <avi@...o.co.il>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: FP in kernelspace

Jiri Slaby wrote:
>
> Hello,
>
> I have a driver written for 2.4 + RT patches with FP support. I want 
> it to work
> in 2.6. How to implement FP? Has anybody developped some "protocol" 
> between KS
> and US yet? If not, could somebody point me, how to do it the best -- 
> with low
> latency.
> The device doesn't generate irqs *), I need to quickly respond to 
> timer call,
> because interval between two posts of data to the device has to be 
> equal as much
> as possible (BTW is there any way how to gain up to 5000Hz).
> I've one idea: have a thread with RT priority and wake the app in US 
> waiting in
> read of character device when timer ticks, post a struct with 2 floats 
> and
> operation and wait in write for the result. App computes, writes the 
> result, we
> are woken and can post it to the device. But I'm afraid it would be 
> tooo slow.
>
> *) I don't know how to persuade it (standard PLX chip with unknown 
> piece of
> logic behind) to generate, because official driver is closed and _very_
> expensive. Old (2.4) driver was implemented with RT thread and timer, 
> where FP
> is implemented within RT and computed directly in KS.
>
> So 2 questions are:
> 1) howto FP in kernel
>
kernel_fpu_begin();
c = d * 3.14;
kernel_fpu_end();

-- 
error compiling committee.c: too many arguments to function

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