COGSPIN seems to call for a cog number (first parameter).
How do I get the runtime to pick the next available cog?
If it works the same way as the coginit in PASM2 then use a cogid of 16
You can use the predefined constant: COGEXEC_NEW, which is defined as %01_0000 (= 16dec). See the Spin documentation (near the end where the constants are).