linux-kernel - Re: Toggling GPIO at 38Khz

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Message-ID: <Pine.LNX.4.61.0810091350430.9446@chaos.analogic.com>
Date:	Thu, 9 Oct 2008 13:53:22 -0400
From:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
To:	"Dave Hylands" <dhylands@...il.com>
Cc:	"Remy Bohmer" <linux@...mer.net>, "Jon Smirl" <jonsmirl@...il.com>,
	"ARM Linux Mailing List" <linux-arm-kernel@...ts.arm.linux.org.uk>,
	"lkml" <linux-kernel@...r.kernel.org>
Subject: Re: Toggling GPIO at 38Khz

On Wed, 8 Oct 2008, Dave Hylands wrote:

>>> So how do I reliably generate 38Khz without destroying latency in the
>>> system? I also don't want to measure the speed of the code I'm
>>> executing - same code has to run on 90Mhz ARM and 3Ghz Core2. If a do
>>> a loop with nanosleep() I need to know how fast my code is to subtract
>>> it's execution time form the sleep time. The existing LIRC code works
>>> this way and measures it's timing loop.
>>> hrtimers look promising, but hrtimers doesn't have a periodic API. Is
>
> The 38 kHz decoders will actually work across a range of frequencies
> usually about +/- 4 kHz.
>
> If you have a spare UART, you could configure it at 76800 baud and
> just send out an appropriate bit pattern (taking into consideration
> start bit, stop bit, parity, etc.
>
> 115200 baud might also work (3 bit times per 1/38400 of a second). It
> won't be a perfect square wave, butI think it would still work.
>
> You could also do something similar if you have a SPI interface. Just
> set the clock to the right frequency and use the bits sent out to
> generate your pulses.
>
> -- 
> Dave Hylands
> Shuswap, BC, Canada
> http://www.DaveHylands.com/

MIDI runs at 31.25 kBaud PC/AT machines do TX/RX through the
audio boards. Drivers for programming these boards are available
for Linux.

These might work fine.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.25.17 on an i686 machine (4786.81 BogoMips).
My book : http://www.AbominableFirebug.com/
_


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