.globl  main

main:   MOVE.L #20, -(SP)  | push parameter
        JSR c              | call sub
        ADD.L  #4, SP      | fix pointer
        RTS

| parameters have to be pushed onto the stack
| using stack pointer SP
| after the subroutine finishes, the parameters
| have to be taken off the stack by incrmenting SP
| +4 for each parameter (C uses always 4 bytes, even for char)
| multiple parameters: push in reverse order
| the function's return value is always passed in D0