My current project seems just complicated enough that I've been looking at a few simple RTOSes. Since the 8051 architecture is a bit peculiar, I was curious if anyone had any experience they'd like to share. In particular, I'm interested in how the RTOS interacts with Keil features to cope with 8051 limitations. Each task will have to be a new root for overlay analysis, and it's more likely that routines will have to be declared reentrant. And in that case, the RTOS has to deal with the compiler-specific simulated stacks, as well as the 8051 SP. So, I'm interested in how much havoc using an RTOS wreaks on the code size and space, as well as how smoothly the RTOS integrates with Keil conventions. I've looked at four options so far. I presume Keil's RTX51 works well with their own compiler :) The third-party libraries are a bit more of a concern. CMX has a number of recommendations on the board for their TCP/IP stack, but I didn't see any discussion of the RTOS kernel (RTX) itself. Their documentation is less than encouraging, but the answers to my pre-sales questions seemed to indicate they did understand the problems. u/COS has some advantages, but generic, and seems a bit more "traditional" in its expectations from the processor. (Not to mention some unfortunate choices for variable names like "pdata", making it a bit more of a chore to port.) Salvo looks like a good option for simple systems, especially ones that you might not consider for an RTOS, but the fact that many of the functions can only be called from the top level of a task (instead of inside a function) seemed to me like it would be a problem in more complex systems. Anyone have some thoughts they'd like to share?