Saturday, May 29, 2010

Adding Interrupts to uCOS-II Running on Microsoft Windows

How to Simulate Interrupts?

In the past few days, I was asked that question many times. So, I decided to make a small software example to show how uCOS-II interrupts can be simulated under Windows.

I modified the uCOS-II port to support 8 interrupts at the same level of priority. Moreover, these interrupts can occur simultaneously but their ISR execution order depends on the implementation. I followed the uCOS-II tasks's priority schema with interrupts (i.e. the smaller the interrupt number, the faster it will be executed).

The implementation core is done by creating a Win32 thread as a generic IRQ handler in os_cpu.c. In addition, 2 utilities were added in the file pc.c. They are used to register and unregister user ISRs. ISRs will be written only in C.

Testing the Interrupts Implementation

My test code is based on the 1st example in uCOS-II book. I modified this code to have 5 tasks with the highest priority to be interrupt-driven. Each task of the 5 will wait for a semaphore before printing its number on the screen. ISRs will trigger these tasks by signaling the semaphores. The test code can be found here.

To automate this test, I wrote a utility that generates these 5 interrupts randomly every 2 milliseconds. The code for this utility can be found here. I just run my test code then run the interrupt generation utility. To distinguish the interrupt-driven tasks from others, I modified their code to print their IDs in a new color scheme. The interrupt generation utility code is found here.

Fig 1 shows the application running with interrupts. Numbers with blue background are those printed by tasks driven by interrupts.

Figure 1: Example 1 Modified to Run with Interrupts