XTAG4 as a cheap devboard or add-on

[fabriceo]

Hello
the XTAG4 holds a powerful xu316 and is quite cheap.
I m thinking to different way of using it, either as a standalone board, for example
- a special IO extender or logic analyzer with an USB connection.
- a co-processor (dsp) for an existing XU216/XU316 board by using the xConnect protocol and XL0 wires.
in addition to the main J7 connector, 6 x 1 bit ports are available on a specific GPIO connector (footprint on solder side), including PLL (X1D11) but without level shifter (so at 1V8).

in this topic we could share with the community, findings, limitation or ideas to experiment this.

first thing is to connect its J5 or J6 connector and XL0 to another XTAG4 and try using XRUN... but maybe the embedded firmware or OTP is locking Jtag access ? let see
other possibility is to use the embedded usb firmware upload protocol by leveraging XTAG2 utilities available on the old xcore-github. but is it still compatible ? let see
or we could force it to boot from channel end 0 via XL0 by forcing its X0D06 pin to 1 with a thin wire to 1V8 ... and then just configuring it as an extra node of an existing board ? like an XU332 !

for XMOS team : any encouragement or feedbacks are welcome !

url on the XTAG4 datasheet : https://www.xmos.com/download/XTAG4-Datasheet(2).pdf
url on the XTAG4 design files : https://www.xmos.com/file/xtag-4-releas ... ion=latest
url on XTAG2 utilities : https://github.com/xcore/proj_xtag2 and https://github.com/xcore/sw_logic_analyzer

[CousinItt]

Good luck and keep us posted

[Joe]

Sure, why not. We have some cheaper dev boards in the pipeline that will be easier to use.

Nothing is locked down in the XTAG4 so beware as if you play around with it and erase the flash then it will cease to work as an XTAG4 any more ...

A multi chip application should work but you've got to have all xmos devices in the same JTAG chain so you'd need to connect in to the debug header J6 or TAG-Connect header J5.

Incidentally the XTAG4 has an unpopulated (master) header for using TAG-Connect (J3) which can be used with the following cable to connect to TAG-Connect footprints.

https://www.tag-connect.com/product/tc2030-idc-nl