Raspberry Pi3 / ARM SBC RTOS - Feasibility Study

I am interested in discussing ideas and recommendations about installing an ARM based Small Board Computer (SBC) on to an 8bit ISA bus. The end goal would be allow In Circuit Emulation (ICE) of ISA peripherals using code on the SBC. My target price is $100-150USD for a few hours of your time. The bus would have about 45 bits including control signals and clocks. Not all signals are necessary, but would be a goal to allow as many as possible. I understand that some clock signals are too fast for GPIOs, however I am open to ideas for testing. Current tested SBCs are Pi3, BeagleBone Black, and Pine54. Each has their own issues and advantages. The current issue with all however seems to be with Linux and the scheduler. I can emulate a ROM on the 8bit bus for example, however the GPIO timing is inconsistent in most cases. I have about 850ns to latch address bits. And about 450ns at most to latch the control signals and output data bits. Sometimes my code works fine, then about 5% of the time it seems the scheduler doesn't start to notice GPIO changes for about 1000ns and then starts to process which misses the clock cycle and causes an error/crash. I believe I have two choices. Pause the CPU on each access to allow the SBC time to process requests - which is complex and has its own set of issues. Or possibly the more simple solution would be a RTOS or more real time kernel. NOTE: There has been reports of crosstalk on the Pi3 GPIOs when being pushed too quickly. QUESTION: How can we tell the difference between the scheduler causing a slowness issue or crosstalk on the GPIOs from being pushed too quickly? This could be a critical test to confirm things are stable. I want to discuss ideas and options to allow a more real time processing and sampling of the GPIOs. Once discussed and all my questions answered you will be paid in full. We can also discuss other related work (RTOS / edit kernel) which would be paid separately under a separate project. Things I have found that could help: [login to view URL] Force Linux to be more RTOS. Might not be 100% RTOS but if it makes things stable, that is all I care about.