恩,问题解决了。这篇文档有个例子是这么说的:
NET "X" TNM_NET = BRAMS_PORTB( dob* ) groupB;
The TNM group groupB contains each B port driven by net X, if at least one output on that B port drives a signal matching the pattern dob*.
它说的是 B port drives a signal 而不是driven by a signal,
所以还真是ffs(apa0/fd_sm0)等同于ffs(apa0/sm)
因为FF apa0/fd_sm0的Q端net 就是sm