A similiar way was also known as reti-calling.

If you handle an interrupt and reach a point, which need longer processing time, but without disabling interrupts, simple call a label, which was followed by a single RETI.
Then the CPU was marked as interrupt finished, but the program was continued after this call.
Then on the end do a simple RET to return to the main.
This piece of code has then a higher priority as the main, but lower as all 2 interrupt levels.
So it can be named as a software interrupt with a third interrupt level:

org 23h
ljmp int_sio
...

int_sio:

... do something on interrupt level

lcall do_reti

... do something on level above main

        ret
do_reti:
        reti

Peter