as for a genuine software interrupt I use them often. One example is to fetch incoming UART data at a high priority and process it at a priority between hardware interrupts and main.

This example uses timer 2 as a software interrupt, any/most interrupts can be used

In init set all interrupts except timer 2 to a priority other than lowest (0) (modern derivatives 1,2,3, oldies 1).

UART ISR:
; fetch byte to circular buffer, then
setb TF2
reti

then in the timer2 ISR process the byte(s)

OOPS, Sriharsha, your code

ljmp your_routine
reti
....
your_routine:
; your routine code goes here and finally
ret

should be either

1) lcall your_routine
reti
....
your_routine:
; your routine code goes here and finally
ret
or
2) ljmp your_routine
;something else
....
your_routine:
; your routine code goes here and finally
reti

Erik