Research Of Embedded Realtime Operating System Based On 8051

8051 family of microcontrollers is a leading choice for embedded control, which makes it widely used in the embedded system. Traditionally, the task running on the 8051 platform is single threaded, but this concept can't meet the needs of realtime in multi-tasks development. With the ever lasting development of both software and hardware technology, it becomes more than a possibility to apply realtime multi-tasks in the 8051 family. One simple solution is to employ an operating system to link the software applications and hardware together. It is the operating sytem that schedules the tasks, makes them running parallely, thus it speeds up the response.To be different from all the transplanting researches of general purpose 8051 operating system, this paper mainly focuses on the improvement of realtime performance while keeping the operating system's generality and readability. Our study can be divided into two aspects, namely the research and improvement in current reentrance method and interrupt system.To enhance 8051's reentrancy performance, here we present a new method, the page-based reentrant function. Based on the detailed examining of the PDATA's properties, we find the PDATA is a new theoretical solution for C51's reentrant function and can be employed in the multi-tasks. In this paper, we also make a quantitative analysis on the run-time performance of page-based reentrant functions. It shows that our model's bandwidth is 3.75 times of the reentrant stack's, thus the new method makes the executing performance nearly the same as classical compact mode. By taking full advantage of this theory, we carry out a page-based operating system which is suitable for time critical systems. This paper also summarizes the key techniques, main problems and solutions that we meet in the process of building up the page-based operating system.We also improve the system's realtime performance by interrupt handling. On one hand, we use the interrupt-delay-queue to separate the simultaneous writing of key data, thus avoid the operation of disabling interrupt. On the other hand, we use the delta list to improve the tick management of soft timers, which enhances the predictability of ISR. In this paper, we give proof on the time complexity of the delta list with the running features of 8051 platform. The proof demonstrates that the total time complexity of delta list is not better than current algorithm, sometimes even worse. But due to the main load of operation is done outside TICK, it makes the rest load of soft timers management maintain a constant time complexity O(1) in the TICK. Therefor, the enhanced ISR is predictable and grants better real time performance.This paper gives an outlook to the future research in the end.