significant moves towards new parts

Author: SpenceKonde

ChangeLog.md

@@ -29,7 +29,8 @@ These items are in addition to what was listed under changes already in release.
 * Correct version number to 1.6.0. Due to this confusion (it was 1.6.10 for a loong time, then 1.6.11, then corrected to 1.6.0 (but never released in that time), 1.7.0 will be the next version that brings tool updates (since I need to do a release to make testing work on new parts, which will occur under 1.6.x versions, and once I have the other things sorted out for the tooling issues, that's the signal to release 1.7.0; 1.6.0 in turn gets released when I think the EB and DU parts (less USB - I dont know USB) are close enough to working that they will benefit from automated testing. As of 9/9/2025, I can fail to compile blink on all EB parts, and I think I've got most of the work done to add support for failing to compile on DU parts as well as early as today. )
 * Fix variant files again.
 * Fix MAX38903 library (I was trying to use one of the damned boards!)
-
+* Remove the UPDI as GPIO pin option from non-optiboot parts because an analysis revealed that there was no configuration in which DxCore could be used in it's present form with the UPDI as GPIO option selected could be used with supported hardwae to prodice results other than bricked chips that core and supported hardware is unable to recover. Accordingly, these options should not be left as traps for the unwary.
+* Major documentation improvements focusing on main README.md.
 
 ### 1.5.11 (Emergency fix)
 * At some point in the recent past, I must have angered the gods of C, and suddenly millis disabled stopped working - the system would hang (actually, with in-depth investigation, it was shown to be bootlooping - before it called init(), it was calling 0x0000 (a dirty reset) instead of eliding a weakly defined function with nothing in the body except a return, or with an empty body. Why was it doing this? And why only when millis was disabled?). millis disabled is a key piece of core functionality, necessitating an urgent fix. Moving the definitions into main.cpp resolved this issue. (#485)