CompuServe Messages

[Continued] Actually what is presented is the measurement of the interrupt processing without an operating system present. This is the time which would be subtracted from the interrupt processing time with an operating system. The result would be the latency introduced by the operating system. Even that might not fully measure the interrupt latency. Some real- time operating systems directly control the interrupt controller chip. In these cases the operating system receives the interrupt, determines the level, and then invokes the user supplied interrupt driver. This mode of operation would be necessary when additional hardware control was required to ensure the interrupt driver was available for usage. An example would be in a bank switched memory environment. The interrupt driver might be in a bank that was switched out at the time the interrupt occurred. This would require the operating system to switch in the interrupt driver. I cannot see how to measure the interrupt latency through software techniques. By its definition the interrupt latency can only occur when the operating system is executing. Invoking a software interrupt or even causing a hardware interrupt (such as raising a serial port control signal which is looped back into the serial port) from a task are invalid situations, by definition. Sincerely, Rudyard Merriam Consultant Compusult, Inc. Houston, Tx.