1. LPC2148 ARM7 myKernel Details
- Bhavin Kamdar

2. Keil’s RTX Kernel Features
Active Tasks
250
Scheduling
Round-Robin,Premeptive
Task Priorities
1-250
Kernel RAM space
< 300 bytes
RAM space for task
TotalStackSize+52 bytes
Task Stack space
On-demand
Semaphores/Mutex
Yes
User timers
Unlimited

3. TotalStackSize+RAM variables
MyKernel Features
Active Task 8
Scheduling
Round-Robin
Kernel RAM space
256 bytes
RAM space per task
TotalStackSize+RAM variables
Stack Size
512 bytes per task
Semaphores/Mutex
Yes
User Timers
Yes (Limited)
Hardware RTC

4. myKernel Memory map
The first bytes of RAM space is reserved for the kernel and task stack
Each task is assigned 512 bytes of stack (512 * 8=4096 bytes)
The kernel requires 256 bytes of memory to store task stack pointers, task return addresses and other scheduler variables

5. myKernel Scheduler
The scheduler for myKernel is written completely in assembly to have full control over task stack and context switching.
Scheduler executes in privilged mode of ARM whereas all task are executed in user mode only.
Two complementary functions are provided in scheduler to add and remove tasks.

6. myKernel Scheduler (cntd)
Each task is given a time slice of 10ms
The task context during a task switch is saved and retrieved from the task stack only
Scheduler identifies task by a 8 bit process ID (PID).

7. Mutex / Task lists
Each peripheral (UART0, GLCD, MMC and BT module) has its own binary semaphore
Semaphore checking is implemented in assembly to provide true Read-while-write access
Also each peripheral has an optional task list which allows access to peripheral in turn.