Semaphores (INT 21h, C5h - Novell NetWare 4.6)

        Entry:
          AH = C5h
          AL = subfunction
               00h open semaphore
                    DS:DX -> semaphore name
                    CL = initial value
               01h examine semaphore
                   Return: CX = semaphore value (sign extended)
                           DL = open count
               02h wait on semaphore
                    BP = timeout in timer ticks (1/18 sec)
               03h signal semaphore
               04h close semaphore
          CX:DX = semaphore handle (except function 00h)
        Return:
          AL = error code
          if function 00h
             CX:DX = semaphore handle
             BL = open count