And to Erik I will say I have developed applications in very small micros most of my working life. Never once did I use an off the shelf RTOS so I do understand his point of view. Off hand I cannot think of a current specific application in a 4K ROM 128 byte RAM 8051 that would use the RTOS I am developing. However I can give an example of one I did before CMOS versions of the 8051 were available. It used an RCA 1802, the first CMOS micro and 8K ROM and 128 bytes RAM. This was in the early 1980s when that was a lot of ROM and RAM. The product was a predecessor of today's mobile phones and was essentially a cordless phone box. It could handle four handsets making calls and 16 more in a queue. The radio system used a 2mS period TDM system. The micro handled four displays and keypads simultaneously, checked numbers against a fraud file, collected call charge information and tranmitted this over a serial link every hour. I did not realise it at the time but I wrote a time triggered cooperative scheduler and it, plus all the application code, fitted into 6K of code.

Ian