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Packet Shooter


What is it?

This is an alternate firmware load for the OpenTracker hardware that functions as a basic, general-purpose AX.25 packet sender. The system accepts frames in KISS format, one at a time, and transmits the queued data as soon as the channel is clear. With a buffer size of only 160 bytes and no receive capability, it's not going to take the place of a real TNC for most applications. But if you're just interested in sending packet radio data with a Basic Stamp or PIC, this is an easy and inexpensive way to do it.

Setup and Usage

An OpenTracker can be loaded with the Packet Shooter firmware using the otwincfg.exe configuration program. On startup, just check the 'erase and load' box, select the com port, and point it to the firmware image when it prompts for a file. It'll complain that the device type is not supported - that's fine, as there's nothing to configure. You can use the same procedure to reload the standard OpenTracker firmware later if you want to switch back.

The serial port baud rate is fixed at 4800 baud. The device implements very basic Xon/Xoff flow control - it'll send an Xon at startup, an Xoff after buffering a packet to be sent, and an Xon when the packet has been transmitted.

The Packet Shooter supports only KISS port #0, and accepts two KISS commands: TXDELAY and EXIT. The TXDELAY command (0x1) should be followed by a single byte indicating the desired delay between key-up and transmission, in roughly 10 ms increments. The EXIT command (0xff) causes the device to pass control to the bootloader program and reset itself.

Hardware Required

This firmware will run on the regular OpenTracker kit. If you're embedding it in something else, you can get by with just the microcontroller and oscillator.

What's with the name?

It was late, I was tired, and I had to name it something. I think it was probably inspired on some level by the Salad Shooter.