(BELOW WRITTEN BY DANIEL FREAD)
This project includes two schedulers based on the Arm® Cortex®-M0+ processor architecture. They function very similarly:
- Each schedules 3 tasks
- Task 1 flashes the green LED at ~5Hz
- Task 2 flashes the blue LED at ~5Hz
- Task 3 flashes the red LED at ~5Hz
- Each schedules round robin by default
- Each scheduler can let the programmer set default priority levels for each task, which correlate directly to the amount of time slices allocated to each task
- Tasks are scheduled using context switching in assembly
Both schedulers have their own custom feature that differentiates them:
- multitask_prio: Each task can request a priority level change from their default value from the processor. This is always granted as of the current version of the scheduler.
- multitask_sleep: Each task can put itself to sleep and therefore relinquish their time slices to a different task that is awake. Still scheduled round robin, but when the scheduler detects the task is asleep, it immediately swaps to the next task. If all tasks are asleep, the scheduler 'times out' and swaps to a NO_OP state. The scheduler will continuously search for a task that has awaken while in NO_OP, and switch to the latest task found to be awake on next SysTick.
These custom features were made utilizing the SVC function (SuperVisor Call) in ARM assembly. As such, the arguments for these functions are limited from 0-255. The units for the arguments are time slices (about 1/3 of a second).
(BELOW WRITTEN BY DOUGLAS SUMMERVILLE)
Bare Metal Development Environment for FRDM-KL25z Board
This is the bare metal development environment used in the course Embedded Systems Design at Binghamton University. As such, it is intentionally meant to be "empty" in the sense that there are no drivers or example code for the board, other than a simple driver for the red LED (of the RGBLED). It comprises a generic Makefile that will build a project, a linker script, startup code, and some Freescale header files.
The Makefile has a configuration define to disable the reset functionality of the single pushbutton (so it can be used as I/O since there are no other switches or buttons). Because of this, it is possible for someone to "brick" the board by configuring the pin as output and driving the reset value, holding the processor in reset. Because of this, PE[1] can be grounded on start-up to halt the start-up sequence, allowing the board to be reprogrammed. If you want to use PE[1] in an application this code needs to be removed from _startup.c. The Makefile also includes a define to enable/disable the WDT.
The target compiler is arm-none-eabi-gcc. To build a project, create driver(s) for the desired hardware device(s) in the directory drivers and place application code in the src subdirectory. For example, a program test_rgbled.c in src that uses the driver files rgbled.c and rgbled.h in drivers use the command
LIBS="redled.o" make testredled.srec
Multiple driver .o files are space-separated within the quotes.
Note that the startup code is squeezed into flash memory before the flash configuration block at 0x0400. If the startup code is modified, it may no longer fit and could over-write the configuration block. There is no check for this. Therfore, if the _startup.c is modified this should be verified (it may fail to link but this has not been tested).