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>Serial testing with ser_filter</TITLE
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><DIV
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><H1
CLASS="SECTION"
><A
NAME="IO-SERIAL-TESTING-WITH-SERFILTER">Serial testing with ser_filter</H1
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="IO-SERFILTER-RATIONALE">Rationale</H2
><P
>Since some targets only have one serial connection, a serial testing harness
needs to be able to share the connection with <SPAN
CLASS="APPLICATION"
>GDB</SPAN
>
(however, the test and <SPAN
CLASS="APPLICATION"
>GDB</SPAN
> can also run on separate
lines).</P
><P
>The <I
CLASS="FIRSTTERM"
>serial filter</I
> (<SPAN
CLASS="APPLICATION"
>ser_filter</SPAN
>)
sits between the serial port and <SPAN
CLASS="APPLICATION"
>GDB</SPAN
> and monitors
the exchange of data between <SPAN
CLASS="APPLICATION"
>GDB</SPAN
> and the target.
Normally, no changes are made to the data.</P
><P
>When a test request packet is sent from the test on the target, it is
intercepted by the filter.</P
><P
>The filter and target then enter a loop, exchanging protocol data between
them which <SPAN
CLASS="APPLICATION"
>GDB</SPAN
> never sees.</P
><P
>In the event of a timeout, or a crash on the target, the filter falls
back into its pass-through mode. If this happens due to a crash it should be
possible to start regular debugging with <SPAN
CLASS="APPLICATION"
>GDB</SPAN
>. The
filter will stay in the pass-though mode until <SPAN
CLASS="APPLICATION"
>GDB</SPAN
>
disconnects.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="IO-SERFILTER-PROTOCOL">The Protocol</H2
><P
>The protocol commands are prefixed with an <TT
CLASS="LITERAL"
>"@"</TT
>
character which the serial filter is looking for. The protocol
commands include:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>PING</TT
></DT
><DD
><P
>Allows the test on the target to probe for the filter. The
filter responds with <TT
CLASS="LITERAL"
>OK</TT
>, while
<SPAN
CLASS="APPLICATION"
>GDB</SPAN
> would just ignore the
command. This allows the tests to do nothing if they require the
filter and it is not present.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CONFIG</TT
></DT
><DD
><P
>Requests a change of serial line configuration. Arguments
to the command specify baud rate, data bits, stop bits, and
parity. [This command is not fully implemented yet - there is no
attempt made to recover if the new configuration turns out to
cause loss of data.]</P
></DD
><DT
><TT
CLASS="LITERAL"
>BINARY</TT
></DT
><DD
><P
>Requests data to be sent from the filter to the
target. The data is checksummed, allowing errors in the transfer
to be detected. Sub-options of this command control how the
data transfer is made:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>NO_ECHO</TT
></DT
><DD
><P
>(serial driver receive test) Just send data from the
filter to the target. The test verifies the checksum and
PASS/FAIL depending on the result. </P
></DD
><DT
><TT
CLASS="LITERAL"
>EOP_ECHO</TT
></DT
><DD
><P
>(serial driver half-duplex receive and send test) As
<TT
CLASS="LITERAL"
>NO_ECHO</TT
> but the test echoes back the
data to the filter. The filter does a checksum on the
received data and sends the result to the target. The test
PASS/FAIL depending on the result of both checksum
verifications.</P
></DD
><DT
><TT
CLASS="LITERAL"
>DUPLEX_ECHO</TT
></DT
><DD
><P
>(serial driver duplex receive and send test) Smaller
packets of data are sent back and forth in a pattern that
ensures that the serial driver will be both sending and
receiving at the same time. Again, checksums are computed
and verified resulting in PASS/FAIL.
</P
></DD
></DL
></DIV
></DD
><DT
><TT
CLASS="LITERAL"
>TEXT</TT
></DT
><DD
><P
> This is a test of the text translations in the TTY layer.
Requests a transfer of text data from the target to the filter
and possibly back again. The filter treats this as a binary
transfer, while the target ma be doing translations on the
data. The target provides the filter with checksums for what it
should expect to see. This test is not implemented yet.
</P
></DD
></DL
></DIV
><P
>The above commands may be extended, and new commands added, as
required to test (new) parts of the serial drivers in
<SPAN
CLASS="PRODUCTNAME"
>eCos</SPAN
>.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="IO-SERFILTER-SERIAL-TESTS">The Serial Tests</H2
><P
>The serial tests are built as any other eCos test. After running the
<B
CLASS="COMMAND"
>make tests</B
> command, the tests can be found in
<TT
CLASS="FILENAME"
>install/tests/io_serial/</TT
></P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>serial1</TT
></DT
><DD
><P
>A simple API test.</P
></DD
><DT
><TT
CLASS="FILENAME"
>serial2</TT
></DT
><DD
><P
>A simple serial send test. It writes out two strings, one
raw and one encoded as a <SPAN
CLASS="APPLICATION"
>GDB</SPAN
>
O-packet</P
></DD
><DT
><TT
CLASS="FILENAME"
>serial3</TT
> [ requires the serial filter ]</DT
><DD
><P
>This tests the half-duplex send and receive capabilities
of the serial driver. </P
></DD
><DT
><TT
CLASS="FILENAME"
>serial4</TT
> [ requires the serial filter ]</DT
><DD
><P
>This test attempts to use a few different serial
configurations, testing the driver's configuration/setup
functionality. </P
></DD
><DT
><TT
CLASS="FILENAME"
>serial5</TT
> [ requires the serial filter ]</DT
><DD
><P
>This tests the duplex send and receive capabilities of the
serial driver. </P
></DD
></DL
></DIV
><P
>All tests should complete in less than 30 seconds.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="IO-SERFILTER-USAGE">Serial Filter Usage</H2
><P
>Running the ser_filter program with no (or wrong) arguments results in
the following output:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>Usage: ser_filter [-t -S] TcpIPport SerialPort BaudRate
or: ser_filter -n [-t -S] SerialPort BaudRate
-t: Enable tracing.
-S: Output data read from serial line.
-c: Output data on console instead of via GDB.
-n: No GDB. </PRE
></TD
></TR
></TABLE
><P
>The normal way to use it with GDB is to start the filter:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>$ <TT
CLASS="USERINPUT"
><B
>ser_filter -t 9000 com1 38400</B
></TT
></PRE
></TD
></TR
></TABLE
><P
>In this case, the filter will be listening on port 9000 and connect to the
target via the serial port <TT
CLASS="LITERAL"
>COM1</TT
> at 38400 baud. On a UNIX
host, replace "<TT
CLASS="LITERAL"
>COM1</TT
>" with a device such as
"<TT
CLASS="FILENAME"
>/dev/ttyS0</TT
>".</P
><P
>The <TT
CLASS="OPTION"
>-t</TT
> option enables tracing which will cause the
filter to describe its actions on the console.</P
><P
>Now start <SPAN
CLASS="APPLICATION"
>GDB</SPAN
> with one of the tests as an
argument:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>$ <TT
CLASS="USERINPUT"
><B
>mips-tx39-elf-gdb -nw install/tests/io_serial/serial3</B
></TT
></PRE
></TD
></TR
></TABLE
><P
>Then connect to the filter:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>(gdb) <TT
CLASS="USERINPUT"
><B
>target remote localhost:9000</B
></TT
></PRE
></TD
></TR
></TABLE
><P
>This should result in a connection in exactly the same way as if you
had connected directly to the target on the serial line.</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>(gdb) <TT
CLASS="USERINPUT"
><B
>c</B
></TT
></PRE
></TD
></TR
></TABLE
><P
>Which should result in output similar to the below:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>Continuing.
INFO: <BINARY:16:1!>
PASS: <Binary test completed>
INFO: <BINARY:128:1!>
PASS: <Binary test completed>
INFO: <BINARY:256:1!>
PASS: <Binary test completed>
INFO: <BINARY:1024:1!>
PASS: <Binary test completed>
INFO: <BINARY:512:0!>
PASS: <Binary test completed>
...
PASS: <Binary test completed>
INFO: <BINARY:16384:0!>
PASS: <Binary test completed>
PASS: <serial13 test OK>
EXIT: <done></PRE
></TD
></TR
></TABLE
><P
>If any of the individual tests fail the testing will terminate with a
<TT
CLASS="COMPUTEROUTPUT"
>FAIL</TT
>.</P
><P
>With tracing enabled, you would also see the filter's status output:</P
><P
>The <TT
CLASS="LITERAL"
>PING</TT
> command sent from the target to determine the
presence of the filter:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>[400 11:35:16] Dispatching command PING
[400 11:35:16] Responding with status OK</PRE
></TD
></TR
></TABLE
><P
>Each of the binary commands result in output similar to:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>[400 11:35:16] Dispatching command BINARY
[400 11:35:16] Binary data (Size:16, Flags:1).
[400 11:35:16] Sending CRC: '170231!', len: 7.
[400 11:35:16] Reading 16 bytes from target.
[400 11:35:16] Done. in_crc 170231, out_crc 170231.
[400 11:35:16] Responding with status OK
[400 11:35:16] Received DONE from target.</PRE
></TD
></TR
></TABLE
><P
>This tracing output is normally sent as O-packets to <SPAN
CLASS="APPLICATION"
>GDB</SPAN
> which will display the tracing text. By using the
<TT
CLASS="OPTION"
>-c </TT
> option, the tracing text can be redirected to the
console from which ser_filter was started.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="IO-SERFILTER-FAILURES">A Note on Failures</H2
><P
>A serial connection (especially when driven at a high baud rate) can garble the
transmitted data because of noise from the environment. It is not the job of
the serial driver to ensure data integrity - that is the job of protocols
layering on top of the serial driver. </P
><P
>In the current implementation the serial tests and the serial filter are
not resilient to such data errors. This means that the test may crash or hang
(possibly without reporting a <TT
CLASS="COMPUTEROUTPUT"
>FAIL</TT
>). It also
means that you should be aware of random errors - a <TT
CLASS="COMPUTEROUTPUT"
>FAIL</TT
> is not necessarily caused by a bug in the serial driver.</P
><P
>Ideally, the serial testing infrastructure should be able to distinguish
random errors from consistent errors - the former are most likely due to noise
in the transfer medium, while the latter are more likely to be caused by faulty
drivers. The current implementation of the infrastructure does not have this
capability.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="IO-SERFILTER-DEBUGGING">Debugging</H2
><P
>If a test fails, the serial filter's output may provide some hints about
what the problem is. If the option <TT
CLASS="OPTION"
>-S</TT
> is used when starting
the filter, data received from the target is printed out: </P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SCREEN"
>[400 11:35:16] 0000 50 41 53 53 3a 3c 42 69 'PASS:<Bi'
[400 11:35:16] 0008 6e 61 72 79 20 74 65 73 'nary.tes'
[400 11:35:16] 0010 74 20 63 6f 6d 70 6c 65 't.comple'
[400 11:35:16] 0018 74 65 64 3e 0d 0a 49 4e 'ted>..IN'
[400 11:35:16] 0020 46 4f 3a 3c 42 49 4e 41 'FO:<BINA'
[400 11:35:16] 0028 52 59 3a 31 32 38 3a 31 'RY:128:1'
[400 11:35:16] 0030 21 3e 0d 0a 40 42 49 4e '!..@BIN'
[400 11:35:16] 0038 41 52 59 3a 31 32 38 3a 'ARY:128:'
[400 11:35:16] 0040 31 21 .. .. .. .. .. .. '1!' </PRE
></TD
></TR
></TABLE
><P
>In the case of an error during a testing command the data received by the
filter will be printed out, as will the data that was expected. This allows
the two data sets to be compared which may give some idea of what the problem
is.</P
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