I want to know in my ISR whether the last signal was not received. os_send_signal() returns NOT_OK in this situation, however looking at the source for RTX166 full, it looks like the isr_send_signal() implementation returns OK in the same situation. (source code located in path ...\keil\c166\rtx166\source\common\rtxisig.c, line 84 - isr_send_signal(), and ...\keil\c166\rtx166\source\common\rtxsig.c, line 94 - os_send_signal().) Has anyone encountered this? What can be done about it? What does Keil say about this issue? It seems like this is a serious defect in the isr_send_signal() implementation!