By the way, I am adapting said “core” to include also XIAO RP2040 (borads.txt and variant files) so … in the future I will use only the Earle F. Philhower “core and NOT the buggy Seeedstudio “core” 
Guglielmo
P.S.: Just compiled for XIAO RP2040, without errors, a test program with 3 serial, semaphores and “multi-core” control … 