UsbJtagEmu

intro

this is a project that i've thought about for a while. i've upgraded it from an idea to a potential project since the ADI EZKITs have this built in. There is a USB header on the board that contains ADIs 'proprietary' USB-JTAG emulator. This emulator is most likely a bit-banged implementation of the jtag protocol which is embedded on the EZKIT (my guess is in the FPGA). The emu takes commands over USB and writes them to the JTAG bus.

This is the same thing that jtagtools, jtager... do expect it is 'embedded' in your computer and uses the lpt port for digital IO. The real simple ones don't even have buffered IO, the 'complex' ones are simply buffered IO. It then stands that the JTAG protocol could be stripped from the application logic pretty easily. rather than bit-bang the jtag pins (TDI, TDO, TCLK...) "jtag program" could send a command to a small embedded system that then uses it's IO to strobe the JTAG bus as needed.

the WIGGLER and other lpt jtag devices are pretty common but require a parallel port. it's not that big of a deal yet but they are getting rarer on motherboard. this would be a project to create a USB device that (with a simple patch) would still work with the openwince jtagtools (or the blackfin version) and hopefully jtager. the common WIGGLER is just a buffered bit-banged jtag interface so i should be simple enough to embed the bit banging and create a serial interface.

why rs232?

serial interface? i thought you said USB? the FTDI USB uarts simplify this project considerably and allow me to develop a RS232 device and then easily make it USB (rather than deal with that protocol). as of 2.4 or 2.6 this device is supported by linux (/dev/ttyUSBx) and there is a free driver for windows so i feel that it is a good solution.

progress

i've thought up the idea and am working on the implementation... i'm currently to busy with being newly married and the blackfin.

advantages

the embedded system will only contain the jtag protocol and not information about the chip it is controlling. That allows future upgrades and addition drivers to be added without having to reflash the JTAG dongle. The advantage of this system (say over ADIs built in one) is that it could be used for multiple chips. This saves you from buying a jtag device for every chip you target but eliminates the need for a parallel port on your development system.

-- ChristopherPepe - 29 Jul 2006