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.\" -*- nroff -*-
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.\" $Id: set_ftdi_lat.1 547 2013-12-29 13:10:07Z mueller $
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.\"
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.\" Copyright 2010-2013 by Walter F.J. Mueller
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.\"
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.\" ------------------------------------------------------------------
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.
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.TH SET_FTDI_LAT 1 2013-12-26 "Retro Project" "Retro Project Manual"
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.\" ------------------------------------------------------------------
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.SH NAME
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set_ftdi_lat \- set latency timer in FTDI USB UART or FIFO
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.\" ------------------------------------------------------------------
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.SH SYNOPSIS
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.
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.SY set_ftdi_lat
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.RI [ dev ]
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.RI [ time ]
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.YS
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.
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.\" ------------------------------------------------------------------
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.SH DESCRIPTION
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\fBNote:\fP command is obsolete when kernel 2.6.32 or newer is used.
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See NOTES section.
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.
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.PP
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FTDI USB UART or FIFO adapters of type FT232, FT245, and other similar
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models have a latency timer which controls the maximal time between reception
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of a byte by the UART or FIFO and the emission of a USB frame. The default
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is 16 msec on kernels prior to 2.6.32 and can lead to unsatisfactory
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response times.
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The
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.B set_ftdi_lat
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script allows to set this latency timer via a node in the \fI/sys\fP
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virtual file system, specifically
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.IP "" 4
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.I /sys/bus/usb-serial/devices/ttyUSBn/latency_timer
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.
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.PP
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The first optional argument \fIdev\fP allows to specify the device name
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in the form \fIUSBn\fP with the default \fIUSB0\fP. The second optional
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argument \fItime\fP allows to specify the new value of the latency timer,
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given in msec. Default is 1 msec.
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.
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.\" ------------------------------------------------------------------
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.SH EXIT STATUS
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If device tty\fIdev\fP is not found or the entry in \fI/sys\fP is not
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writable an exit status 1 is returned.
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.\" ------------------------------------------------------------------
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.SH EXAMPLES
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In general the command is given via \fBsudo\fP(8) like
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.EX
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sudo set_ftdi_lat USB0 1
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.EE
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.\" ------------------------------------------------------------------
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.SH "SEE ALSO"
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.BR sudo (8)
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.
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.\" ------------------------------------------------------------------
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.SH NOTES
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For linux kernel 2.6.32 or newer the default is 1 ms already. On all
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up-to-date systems therefore no need to use this command.
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.
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.\" ------------------------------------------------------------------
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.SH AUTHOR
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Walter F.J. Mueller
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