From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Stalin Kenny" <stalinlinux@gmail.com>
Subject: Re: function read() isn't quick enough for reading in ttyS*
Date: Mon, 4 Aug 2008 00:44:13 -0500
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To: Federico Tula Rovaletti <fedetula@gmail.com>
Cc: linux-c-programming@vger.kernel.org

> In a program I'm writing in c, when I use the read() function for
> reading a byte in the serial port with a configuration: 115200 bps,
> 8N2
>
> takes from 2ms to 6ms (aleatory, even if read up to 10 bytes takes the
> same time), which is  too long.
> (ioctl(fd, FIONREAD, &bytes)  last the same)
>
> This is the time is suppose to last:
> 8 bits: data
> 2 bits: stop
> 1 bit: start
> time = ((8+2+1)bits/115200bps) = 0.095ms,
>
> then when I read the byte with the function inb_p() takes ~ 0.1ms
> which is perfect, what I'm needing for my project.
>

I guess the context switch that is taking place when you issue ioctl
is contributing to the extra time that you are noticing.

Stalin