This is an old topic but would like to add some comments that can be useful to someone having this kind of issues. I have an expansion board 3 with a Wipy, using the SD card and some sensors, and everything is working well being powered throu USB or battery. I had some issues that were fixed by following these steps: When powered by battery, P19 and P20 are affected by RTS and CTS respectively, and it was blocking one sensor I have connected to those pins. Removing those jumpers from Expansion Board resolved this issue. Don't use P8 with any sensor if you are using SD card. Looking at the Wipy3 pinout, I suppose the same is true for P3, P9 and P10. Even thou, P10 is also connected to the user button, then I configured it as an input pin with pull=PULL-UP, and avoid read/write SD operations and user button clicks at the same time. Also, this post helped me with a weird behavior of user button when using the battery: https://forum.pycom.io/topic/7364/exp-board-user-push-button/3?_=1648562954689 I connected the 10K pull-up resistor to P8 as indicated in the expansion board documentation, but honestly, I don't understand why it's needed. Most of these "tricks" are not clearly documented and I found them reading several posts and connecting ideas between them. In my opinion, Pycom boards are very good in general (with a very few details that could be improved), but as said in many places, its documentation should be reviewed to add many things like these that one has to chase reading somewhere else or by try/fail methods.

@robert-hh I just connected power drectly. That works, now I have to do some soldering in order to check if it works together with the level-shifter. Thx so far!

@dan Yep I have never put anything in boot.py, have always had main.py run without intervention.

@catalin I finally managed to perform tests of releases between 1.14.0.b1 and 1.18.0.b1. Otii ARK traces are available here: https://drive.google.com/open?id=1kIZL0HJHn_dEIPDM_jv6fEhDhb_Ukfqj Significant execution time increase occured between versions: 1.17.0.b1: MP: d0dc708a0197d2900a5620648725794a1fb5c8f3 IDF: 3b54cd7473aefdb8b75531a21ce340c4bd2221da and 1.17.2.b1: MP: 1bf377b08e2162e8534b6cbe78dcdeeb930f64b8 IDF: 4eab4e1b0e47c73b858c6b29d357f3d30a69c074

@jmarcelino The only thing connected during update is PyTrack module which I use to connect USB.

@jonasde For verification, you can use a different and dump terminal software like Putty (Windows), screen (mac, linux) or picocom (Linux). Just make sure that any kind of handshake is disabled. For fil etranfer you can use an ftp client like filezilla or fireftp.

@seb OK, I think you are right that it is a power supply issue. I've tried the same cable directly with a USB power supply and haven't seen the issue happen again. So it might be for some reason that the Macbook USB port (or adapter) cannot supply enough power. Will try it with a LiPo connected.

Hi Jardar, The docs for secure boot are published/duplicated here: https://docs.pycom.io/chapter/advance/encryption.html Encryption key can't be changed, nor re-generated (that's why they should be kept safe). The 3 times limitation is valid just in the following case: the firmware binaries are written not-encrypted using USB (uart), and the ESP32 encrypts all the partitions marked as encrypted (and an ESP32 efuse has to burned. In all the other cases, like OTA update, ftp transfer, the encryption/decryption is made transparently, without the encryption counter being increased.