In preparation for production testing, I've written two new utilities: - atrf-proxy gives access to an ATBEN/ATUSB card via TCP
- atrf-path measures the difference between the nominal transmit power of one ATBEN/ATUSB card and the received signal strength of another such card atrf-path makes one card emit a constant signal and measures the strength of the signal received by the other. Then it switches both cards to the next channel and repeats the procedure. This is basically a poor man's spectrum analyzer with tracking generator. atrf-path can dump the results to a file or display them with SDL in a Ben-sized window. One can also specify a profile of acceptable values and then perform a pass/fail test. Here's a screenshot: http://downloads.qi-hardware.com/people/werner/wpan/tmp/atrf-path.png The white line shows the measured signal strength. Frequency is along the x axis, signal strength along the y axis. The red lines mark the upper and lower boundary. The green disc indicates that the white line is within the limits. Here is the profile I used in this example: http://projects.qi-hardware.com/index.php/p/ben-wpan/source/tree/master/tools/atrf-path/profile.example atrf-path needs to talk to two cards. The atrf-* utilities so far assumed that there was only one card: ATBEN if running on a Ben, ATUSB otherwise. Now, we have more choices: - all utilities (except atrf-path) accept an option to select the device: -d driver[:arguments] - on a PC, one can select which USB device to use with -d usb:bus/number, where "bus" is the bus number and "number" is the logical device number. When lsusb -d:1540 shows Bus 001 Device 015: ID 20b7:1540 Qi Hardware ben-wpan, AT86RF230-based the correct option would be -d usb:1/15 - similarly, one can select the USB device by bus and sequence of ports to cross. This is more difficult to use than the above approach, but has the advantage that the numbers stay constant as long as the cabling isn't changed. The syntax of the path is the same as in sysfs, -d usb:bus-port.port...port For example, I have a seven-port USB hub connected to my PC. USB hubs with more than four ports typically contain two cascaded hub chips with four ports each. I've connected an ATUSB card to a port that happens to be on the 2nd chip. The option to reach it is: -d usb:1-3.1.4 This means: bus 1, port 3 (on the PC), then the 1st port of the first chip in the hub, which leads to the second chip, and of this one the 4th port. The driver still checks the product/vendor ID and thus won't cause mayhem if the path leads to some other device. - to select the ATBEN card (which would be the default on a Ben anyway), use -d ben - and now the fun part: with -d net:address[,port] an ATBEN/ATUSB card on a different machine can be accessed. For this, the machine must be reachable via TCP/IPv4, and that machine must run atrf-proxy. To give access to the default card, simply run atrf-proxy without arguments. It will listen on port 5440 (0x1540, like the ATUSB product ID) for an incoming connection. atrf-proxy accepts the -d option as well. Example: if I have atrf-proxy running on my Ben with host name "ben", I can identify the card from the PC with atrf-id -d net:ben In this case, this would produce the same output as running ssh ben atrf-id Now, back to atrf-path. atrf-path needs to talk to two cards at the same time, so it can't just pick the system's default card. Instead, the two cards are specified on the command line, e.g., when we add another Ben called "jlime", with atrf-path net:ben net:jlime This will make it do one sweep at +/- 0.5 MHz in each channel, and print the result on standard output. The +/- 0.5 MHz comes from the limitation that the transceiver can only send a constant test signal at an offset of 0.5 MHz from a channel's center frequency, but not exactly at the channels center frequency. If we're only intrested in one transmit frequency per channel, we can tell atrf-path which one to pick with -T -0.5 or -T +0.5. This also makes the sweep run faster, which is useful with graphical output. The output of atrf-path can be visualized with the "plot" script in ben-wpan/tools/atrf-path/ or by running atrf-path in GUI mode, with the option -g. Our command line is now atrf-path -g -T -0.5 net:ben net:jlime The transceiver's signal strength mesurements have a granularity of 3 dB, which is rather coarse. We can use averaging to get more details: atrf-path -g -T -0.5 net:ben net:jlime 10 We may also want to set the transmit power with the option -p, which accepts a value between 0 (-17 dBm or 20 uW) and 15 (3 dBm or 2 mW). The default is currently to use maximum power, but I'll probably change this. Last but not least, we can set the profile with the option -P: atrf-path -g -T -0.5 -p 0 -P profile.example net:ben net:jlime 10 Next: pass/fail and a playful usage. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
