ISP(ID:7349/isp005)System for graphical communication with satellitesSYstem for graphical communication with satellites References: Systems for Configurable Programming All of the systems described in section 5.2 represent important advances in satellite graphics, but do lack ease of learning and convenient redistribution of processing between the host and satellite. Two on-going research projects have built on this earlier work to develop systems which eliminate these two problems. The projects are van Dam's at Brown University [ 26, 27, 28 ] , and Foley's at the University of North Carolina [ 9, 11, 12 ] . While there are important differences in technique, the similarity of purpose is more important. Both projects' goal is to allow an application programmer to write in a single language as though for two computers sharing a common memory and then assign programs and data to either the host or satellite. Further, this initial configuration (division of labor) can be later "reconfigured" with no reprogramming. The programmer never explicitly deals with in-processor communications. The Brown system (ICOPS, for Interconnected Processing system) allows interprocess communication by means of subroutine calls and passed parameters. It is currently used with a meta level language, and will be eventually used with LSD, Language for System Development [ 1 ] . The hardware is an IBM 360/67 r a 50K bps link, a 32K byte microprogrammed Digital Scientific Meta 4 satellite, with disk and a display processor consist) of a second Meta 4 driving a Vector General. The UNC system (CAGES, Configurable Applications for Graphics Employing Satellites), permits programs to be written a PL/1 subset called PLCD [ 6, 13 ] , and supports interprocess communications not only by calls and parameters, but also by signalled PL/1 conditions and references to variables known both host and satellite. Hardware is an IBM 360/75 host, a bps link, a 56K byte PDP-11/45 with disk, and a Vector General display processor. Both ICOPS and CAGES have resident run-time systems to access references to procedures or data on the other computer, and to apply needed representational conversions to procedure parameters or data, such as converting from ASCII to EBCDIC. This "configurable programming" approach to the use or programmable satellites has a number of desirable attributes as pointed out in [ 12 ] . First, a single programming language i used. The language processors can produce executable code f either the host or satellite. Second, the application programmer does not explicitly p gram inter-CPU communications. Such communications are automatically provided by the run-time system whenever a referee to a non-resident procedure or data element is made. The programmer continues to use the familiar subroutine call or data reference to implicitly initiate the communication. Third, performance data can be used to fine tune the division of labor to minimize response time, host usage charges, some other metric. Fourth, the programmer can conceive of and write the ent application program as a whole, as if it were going to be executed only on one computer, without knowing its eventual configuration. This should be helpful in conceiving of the application as a whole. For execution efficiency' however, he may want to be aware when designing the program structure that it will eventually be distributed. He may also want to optimize performance for what he considers to be likely configurations. Fifth, program configurability is a necessary (but not sufficient) condition for program portability among dissimilar host satellite systems. This is because, when moving to another satellite graphics system, the size of the host and satellite computers may change drastically. Some parts of the application program may have to be moved from the satellite to the host due to memory or other restrictions on the satellite. in Klinger, A.; Fu, K. S.; Kunii, T. L. "Data Structures, Computer Graphics, and Pattern Recognition" (Largely based on IEEE Computer Society conference held in Los Angeles, May 1975) Academic Press, NY 1977 view details |