> Is it normal that I have to mod the pppd (and chat) program

Apparently so.  I've long wondered why the official pppd sources have never
made use of the half-hearted stub that's already present to make this
work right.

It should be possible to get by without modifying chat (though I guess
that assumes that one never uses chat by itself); I just have pppd set
O_NDELAY if both connector && modem are true, then it clears O_NDELAY
just before calling device_script().