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                    Serial Testing with ser_filter

Rationale
~~~~~~~~~
 Since some targets only have one serial connection, a serial testing
 harness needs to be able to share the connection with GDB (however,
 the test and GDB can also run on separate lines).

 The serial filter (ser_filter) sits between the serial port and GDB
 and monitors the exchange of data between GDB and the
 target. Normally, no changes are made to the data.

 When a test request packet is sent from the test on the target, it is
 intercepted by the filter. The filter and target then enter a loop,
 exchanging protocol data between them which GDB never sees.

 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 GDB. The filter
 will then stay in the pass-though mode until GDB disconnects.


Adding A New Platform
~~~~~~~~~~~~~~~~~~~~~
 The file ser_test_protocol.inl contains information about how to run
 the serial tests on supported platforms. When adding a new serial
 driver to eCos, ser_test_protocol.inl should be updated accordingly
 so the driver can be tested.

 The definitions TEST_SER_DEV and TEST_TTY_DEV are set according to
 platform:

  TEST_SER_DEV is the name of the serial device over which the serial
  test protocol runs. The definition should be conditional on all
  required configuration options.

  TEST_TTY_DEV is the name of the TTY device over which the TTY test
  protocol runs. The definition should be conditional on all required
  configuration options. Note that this device is layered on top of a
  serial device and must be conditional on that device's config
  options as well as its own.

 Here's an example for the PowerPC/Cogent where GDB is connected via
 serial connector B:
 
#if defined(CYGPKG_HAL_POWERPC_COGENT)                          \
    && defined(CYGPKG_IO_SERIAL_POWERPC_COGENT)                 \
    && defined(CYGPKG_IO_SERIAL_POWERPC_COGENT_SERIAL_B)
# define TEST_SER_DEV CYGDAT_IO_SERIAL_POWERPC_COGENT_SERIAL_B_NAME
# if defined(CYGPKG_IO_SERIAL_TTY_TTY2)
#  define TEST_TTY_DEV CYGDAT_IO_SERIAL_TTY_TTY2_DEV
# endif
#endif

 
 On some targets it may also be necessary to intialize interrupt
 vectors which are otherwise used by CygMon or an eCos GDB stub to
 monitor characters from the host (looking for Control-C):

#  define SER_OVERRIDE_INT_1 CYGNUM_HAL_INTERRUPT_9
#  define SER_OVERRIDE_INT_2 CYGNUM_HAL_INTERRUPT_10

 These definitions cause the serial test to restore the eCos handler
 on the specified vectors before opening the serial device.


 The file ser_test_protocol.inl also contains an array of serial
 configurations (test_configs). It may be necessary to comment some of
 these out for the platform if the driver or hardware cannot handle
 all the given serial configurations.


The Protocol
~~~~~~~~~~~~
 The protocol commands are prefixed with an @-character which the
 serial filter is looking for. The protocol commands include:

  PING
   Allows the test on the target to probe for the filter. The filter
   responds with OK, while GDB would just ignore the command. This
   allows the tests to do nothing if they require the filter and it is
   not present.

  CONFIG
   Requests a change of serial line configuration. Arguments of the
   command specify baud rate, data bits, stop bits, and parity.

  OPT
   Requests changes in the filter's options. This allows various
   amounts of tracing to be recorded when running tests without
   requiring the filter to be restarted.

  BINARY
   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:

    NO_ECHO (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.

    EOP_ECHO (serial driver half-duplex receive and send test)
     As NO_ECHO 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.

    DUPLEX_ECHO (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.

  TEXT
   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 may 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]

 The above commands may be extended, and new commands added, as
 required to test (new) parts of the serial drivers in eCos. 

 See ser_test_protocol.inl for further details on the protocols.


The Serial Tests
~~~~~~~~~~~~~~~~
 The serial tests are built as any other eCos test. After running the
 'make tests' command, the tests can be found in:

 install/tests/io_serial/

 serial1
  A simple API test.

 serial2
  A simple serial send test. It writes out two strings, one raw and
  one encoded as a GDB O-packet.

 serial3 [requires the serial filter]
  This tests the half-duplex send and receive capabilities of the
  serial driver.
 
 serial4 [requires the serial filter]
  This test attempts to use a few different serial configurations,
  testing the driver's configuration/setup functionality.

 serial5 [requires the serial filter]
  This tests the duplex send and receive capabilities of the serial
  driver.

 All tests should complete in less than 30 seconds.


Serial Filter Usage
~~~~~~~~~~~~~~~~~~~
 Running the ser_filter program with no (or wrong) arguments results
 in the below output:

  Usage: ser_filter [-t -c -g -S] TcpIPport SerialPort BaudRate
   or:   ser_filter -n [-t -c -g -S] SerialPort BaudRate
   -t: Enable tracing.
   -f: Enable filter output tracing.
   -g: Enable GDB tracing.
   -S: Output data read from serial line.
   -c: Output data on console instead of via GDB.
   -n: No GDB.

 The normal way to use it with GDB is to start the filter:

  ser_filter -t 9000 com1 38400

 In this case, the filter will be listening on port 9000 and connect
 to the target via the serial port COM1 at 38400 baud. On a UNIX host,
 replace "com1" with a device such as "/dev/ttyS0".

 The '-t' option enables tracing which will cause the filter to
 describe its actions on the console.

 Now start GDB with one of the tests as an argument:

  $ mips-tx39-elf-gdb -nw install/tests/io_serial/serial3
 
 Then connect to the filter:

  (gdb) target remote localhost:9000

 This should result in a connection in exactly the same way as if you
 had connected directly to the target on the serial line.

  (gdb) load
  ...
  (gdb) cont

 Which should result in output similar to the below:

  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:<serial3 test OK>
  EXIT:<done>

 If any of the individual tests fail the testing will terminate with
 a FAIL.

 With tracing enabled, you would also see the filter's status output: 

 The PING command sent from the target to determine the presence of
 the filter:
  [400 11:35:16] Dispatching command PING
  [400 11:35:16] Responding with status OK

 Each of the binary commands result in output similar to:
  [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.

 This tracing output is normally sent as O-packets to GDB which will
 display the tracing text. By using the -c option, the tracing text
 can be redirected to the console from which ser_filter was started.


 The trace options -f, -g, and -S cause data sent from filter, GDB or
 target to be output in hexadecimal form.


A Note on Failures
~~~~~~~~~~~~~~~~~~
 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.

 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 FAIL). It also means that
 you should be aware of random errors - a FAIL is not necessarily
 caused by a bug in the serial driver.

 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.


Debugging
~~~~~~~~~
 If a test fails, the serial filter's output may provide some hints
 about what the problem is. If the option '-S' is used when starting
 the filter, data received from the target is printed out:

  [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!'

 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.