SYNCLOOP(8) Maintenance Commands and Procedures SYNCLOOP(8)

NAME

syncloop - synchronous serial loopback test program

SYNOPSIS

/usr/sbin/syncloop [-cdlstv] device

DESCRIPTION

The syncloop command performs several loopback tests that are useful
in exercising the various components of a serial communications link.


Before running a test, syncloop opens the designated port and
configures it according to command line options and the specified
test type. It announces the names of the devices being used to
control the hardware channel, the channel number (ppa) corresponding
to the device argument, and the parameters it has set for that
channel. It then runs the loopback test in three phases.


The first phase is to listen on the port for any activity. If no
activity is seen for at least four seconds, syncloop proceeds to the
next phase. Otherwise, the user is informed that the line is active
and that the test cannot proceed, and the program exits.


In the second phase, called the "first-packet" phase, syncloop
attempts to send and receive one packet. The program will wait for up
to four seconds for the returned packet. If no packets are seen after
five attempts, the test fails with an excoriating message. If a
packet is returned, the result is compared with the original. If the
length and content do not match exactly, the test fails.


The final phase, known as the "multiple-packet" phase, attempts to
send many packets through the loop. Because the program has verified
the integrity of the link in the first-packet phase, the test will
not fail after a particular number of timeouts. If a packet is not
seen after four seconds, a message is displayed. Otherwise, a count
of the number of packets received is updated on the display once per
second. If it becomes obvious that the test is not receiving packets
during this phase, the user may wish to stop the program manually.
The number and size of the packets sent during this phase is
determined by default values, or by command line options. Each
returned packet is compared with its original for length and content.
If a mismatch is detected, the test fails. The test completes when
the required number of packets have been sent, regardless of errors.


After the multiple-packet phase has completed, the program displays a
summary of the hardware event statistics for the channel that was
tested. The display takes the following form:

CRC errors Aborts Overruns Underruns In<-Drops-> Out
0 0 0 0 0 0


This is followed by an estimated line speed, which is an
approximation of the bit rate of the line, based on the number of
bytes sent and the actual time that it took to send them.

OPTIONS

The options for syncloop are described in the following table:


Option Parameter Default Description
-c packet_count 100 Specifies the number of
packets to be sent in the
multiple-packet phase.
-d hex_data_byte random Specifies that each packet
will be filled with bytes
with the value of
hex_data_byte.
-l packet_length 100 Specifies the length of each
packet in bytes.
-s line_speed 9600 Bit rate in bits per second.
-v Sets verbose mode. If data
errors occur, the expected
and received data is
displayed.
-t test_type none A number, from 1 to 4, that
specifies which test to
perform. The values for
test_type are as follows: 1:
Internal loopback test.
Port loopback is on.
Transmit and receive clock
sources are internal (baud
rate generator). 2: External
loopback test. Port
loopback is off. Transmit
and receive clock sources
are internal. Requires a
loopback plug suitable to
the port under test. 3:
External loopback test.
Port loopback is off.
Transmit and receive clock
sources are external
(modem). Requires that one
of the local modem, the
remote modem, or the remote
system be set in a loopback
configuration. 4: Test using
predefined parameters. User
defines hardware
configuration and may select
port parameters using the
syncinit(8) command.


All numeric options except -d are entered as decimal numbers (for
example, -s 19200). If you do not provide the -t test_type option,
syncloop prompts for it.

EXAMPLES

Example 1: A sample display of using the syncloop command.

In the following command syncloop uses a packet length of 512 bytes
over the first CPU port:


example# syncloop -l 512 zsh0


In response to the above command, syncloop prompts you for the test
option you want.


The following command performs an internal loopback test on the first
CPU port, using 5000 packets and a bit rate of 56Kbps:


example# syncloop -t 1 -s 56000 -c 5000 zsh0

SEE ALSO

attributes(7), syncinit(8), syncstat(8)

DIAGNOSTICS

device missing minor device number

The name device does not end in a decimal number that can be used
as a minor device number.


invalid packet length: nnn

The packet length was specified to be less than zero or greater
than 4096.


poll: nothing to read


poll: nothing to read or write.

The poll(2) system call indicates that there is no input pending
and/or that output would be blocked if attempted.


len xxx should be yyy

The packet that was sent had a length of yyy, but was received
with a length of xxx.


nnn packets lost in outbound queueing


nnn packets lost in inbound queueing

A discrepancy has been found between the number of packets sent
by syncloop and the number of packets the driver counted as
transmitted, or between the number counted as received and the
number read by the program.

WARNINGS

To allow its tests to run properly, as well as prevent disturbance of
normal operations, syncloop should only be run on a port that is not
being used for any other purpose at that time.

March 6, 2023 SYNCLOOP(8)