Instruction format for ensuring safe execution of display list

Abstract

In a computer controlled graphics system, processes are provided for detecting errors incurred in a display list having variable length instruction/parameter (I/P) sets, the errors occurring during parameterization, transmission, branching, and storage of the display list. Each process includes generating a display list including I/P sets, each I/P set including n parameter words following an instruction word. In each embodiment, a display list is encoded, transmitted, stored in a memory unit, and verified. In one embodiment, the display list is encoded by storing into each instruction word of each I/P set a parity bit of a value representative of the parity of the whole I/P set. In another embodiment, the display list is encoded by storing within each instruction word of each I/P set an m-bit checksum value. The m-bit checksum value is generated by partitioning each I/P set into y m-bit partitions which are summed, ignoring overflow. In a third embodiment, a display list is encoded by appending each I/P set with a checksum word generated by summing the instruction word and each of the n parameter words of each I/P set, ignoring overflows. In each embodiment, the encoded display list is stored in a memory unit and later accessed for verification. In each embodiment, verification is performed by re-performing the respective encoding scheme for each I/P set. Upon detection of an error, corrective action, including a debug message can be taken.