Merry Christmas and Happy New Year. I hope your holidays are filled with friends and of course blinky things.
I posted on Espressif’s forum under bugs for a feature request. At the time that I write this post, there have been 26 views of the request. I hope it gets enough interest that Espressif considers my request.
I soldered a 2 pin header into pins 1 and 2 of the programming connector. I then connected 3.3 Volts to Pin1. I hooked up my Oscilloscope to pin 4 and immediately saw data on the line. Pin 4 is attached to MISO. This is great news, the data is getting through the level shifter. Unfortunately, the waveform shows a lot of noise. Then I switched to 5V and I saw data again, but the firmware crashed very quickly. I started out by assuming the 5 Volts was the problem. So I tried setting it back to 3.3 Volts and the system wouldn’t reboot. Then I disconnected the voltage supply and still not booting. Finally, I disconnected my oscilloscope probe and it would boot again.
The MISO line brings the code from flash into the processor. Any glitch on it could cause crashes/failures. It appears that the scope probe added to the output of the chip was enough to cause a glitch back on the MISO line. This is disappointing, scope probes are very minimal loads. Typically 10pF and 10MΩ on the circuit. That is less than most devices that I would want to program. This is going to take some more time to look at. I need to test with a larger load, and maybe some pullups/pulldowns. I am beginning to think a port expander might be a better choice. It’s still early to make that decision.
I started writing this post on Saturday before Christmas. I didn’t get much done then. I don’t expect to get back to it over new years weekend. So this is the only post for both weeks. I hope you get some value reading this blog.
I am considering the value of this design as it stands. The Raspberry Pi might be a better platform to achieve this goal. Put on a small board that does the level conversion, and generated the programming voltage might be a new direction for the design. The Raspberry Pi has a lot more IO available and more power and RAM. On the other hand, it could turn into a more expensive project because I would want to add an external ADC.
What do you think? Would I attract more software developers if I used the Pi? Is there a direction you would like this project to go?