This post originated from an RSS feed registered with Python Buzz by Phillip Pearson. Original Post: Still trying to get JTAG working with the ESP8266 Feed Title: Second p0st Feed URL: http://www.myelin.co.nz/post/rss.xml Feed Description: Tech notes and web hackery from the guy that brought you bzero, Python Community Server, the Blogging Ecosystem and the Internet Topic Exchange Latest Python Buzz Posts Latest Python Buzz Posts by Phillip Pearson Latest Posts From Second p0st

Good news -- my replacement J-Link is in the mail! Reliable hardware on the way.

In the meantime, I'm still working on my CMSIS-DAP adapter and my ESP8266 board. I'd mis-soldered a 10uF capacitor between TCK and ground (instead of 3V3 and ground), which was stopping anything from working, but after hooking my Saleae box up to the board, I debugged that fairly quickly. I fixed some bugs in the code, but OpenOCD still failed to do the initial chain scan, so something's still broken.

To debug this, I changed tack: OpenOCD also has a "remote_bitbang" driver, where it sends a series of ASCII characters to a TCP socket, to drive a very very simple JTAG adapter. This sounds like a recipe for the worst JTAG performance ever, except that the Teensy 3.2's serial-over-USB performance is very very good, and I saw some pulses as short as 2us in the logic capture, so this should be able to get me ~250 kbit/s, which is certainly good enough for now.

→ Here's the teensy-openocd-remote-bitbang code, on GitHub

It took a bit of messing around with socat on OS X to get it to bridge between a TCP socket and a serial port, but I found the magic set of arguments eventually:

Unfortunately OpenOCD *still* couldn't scan the JTAG chain, and it did get bits out TDO this time, so I still have some debugging to do.

Comment