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.\"  -*- nroff -*-
.\"  $Id: set_ftdi_lat.1 547 2013-12-29 13:10:07Z mueller $
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.\" Copyright 2010-2013 by Walter F.J. Mueller <W.F.J.Mueller@gsi.de>
.\" 
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.
.TH SET_FTDI_LAT 1 2013-12-26 "Retro Project" "Retro Project Manual"
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.SH NAME
set_ftdi_lat \- set latency timer in FTDI USB UART or FIFO
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.SH SYNOPSIS
.
.SY set_ftdi_lat
.RI [ dev ]
.RI [ time ]
.YS
.
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.SH DESCRIPTION
\fBNote:\fP command is obsolete when kernel 2.6.32 or newer is used.
See NOTES section.
.
.PP
FTDI USB UART or FIFO adapters of type FT232, FT245, and other similar
models have a latency timer which controls the maximal time between reception
of a byte by the UART or FIFO and the emission of a USB frame. The default
is 16 msec on kernels prior to 2.6.32 and can lead to unsatisfactory 
response times.
The 
.B set_ftdi_lat
script allows to set this latency timer via a node in the \fI/sys\fP
virtual file system, specifically
.IP "" 4
.I /sys/bus/usb-serial/devices/ttyUSBn/latency_timer
.
.PP
The first optional argument \fIdev\fP allows to specify the device name 
in the form \fIUSBn\fP with the default \fIUSB0\fP. The second optional
argument \fItime\fP allows to specify the new value of the latency timer,
given in msec. Default is 1 msec.
.
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.SH EXIT STATUS
If device tty\fIdev\fP is not found or the entry in \fI/sys\fP is not 
writable an exit status 1 is returned.

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.SH EXAMPLES
In general the command is given via \fBsudo\fP(8) like

.EX
    sudo set_ftdi_lat USB0 1
.EE
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.SH "SEE ALSO"
.BR sudo (8)
.
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.SH NOTES
For linux kernel 2.6.32 or newer the default is 1 ms already. On all 
up-to-date systems therefore no need to use this command.
.
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.SH AUTHOR
Walter F.J. Mueller <W.F.J.Mueller@gsi.de>