When multiple synchronized schedulers are used, the master Frame Scheduler receives the interrupt, and allocates an interrupt group that is used to make the interrupt simultaneously available to the synchronized schedulers.
Note: External output signals can be generated by software using ioctl() to the external interrupt driver. An imaginative designer might think of connecting an external output jack to an external interrupt input jack on the same system, thus creating software-controlled external interrupts as an FRS time base. This would work in principle. However, if user process generating the interrupts are generated by a user process that makes any other system calls, there is a possibility of system deadlock.