There are currently four FreeRTOS ports for Luminary Micro Stellaris Cortex based embedded microcontrollers - one that uses the Sourcery G++ (GCC) tools,
one that uses the ARM Keil tools, another for the IAR tools, and the port presented on this page which uses
Rowley CrossWorks.
Three demo applications are provided for the CrossWorks port, two targeted for the DK-LMS102 development board from Luminary Micro, and one targeted at
the low cost CrossFire LM3S102 board from Rowley Associates. The CrossFire LM3S102 connects
directly to the host computer via the built in USB connector and does not require the use of a separate JTAG interface.
Stellaris is a new range of microcontrollers - the first to be commercially available with a Cortex-M3 core. The LM3S102 is a low cost, low pin count device. It has
2KBytes of RAM and 8KBytes of ROM on chip. An ideal candidate to demonstrate the new co-routine functionality included with FreeRTOS V4.0.0.
The CrossWorks Cortex-M3 demos rely on a driver library and makefile which is licensed separately from FreeRTOS. The license conditions are included within the comments at the
top of the library header files located in the Demo/CORTEX_LM3S102_ROWLEY/hw_include directory. A full copy of the license is available in the same directory.
Upgrading to FreeRTOS V5.0.3: FreeRTOS V5.0.3 introduced the configMAX_SYSCALL_INTERRUPT_PRIORITY configuration option to the Cortex-M3 port. See
the RTOS kernel configuration documentation for full information on this feature.
Upgrading to FreeRTOS V4.8.0: Prior to V4.8.0 the FreeRTOS kernel did not make use of the SVCall interrupt. From V4.8.0 onwards it does.
Therefore, to upgrade an older project to the V4.8.0 standard, a small edit to the startup code is required. To do this, simply install
vPortSVCHandler() in the SVCall position within the interrupt vector table (contained in the startup source file). The demo projects included in the
FreeRTOS download have already been updated so these can be used as an example.
The CrossWorks solution (workspace) for the Luminary Micro port is located in the FreeRTOS/Demo/CORTEX_LM3S102_ROWLEY directory.
The demo application includes an interrupt driven UART test where a co-routine transmits characters that are then received by a task. For correct operation
of this functionality a loopback connector must be fitted to the SER0 connector of the DK-LMS102 prototyping board (pins 2 and 3
must be connected together on the 9Way connector).
The demo application uses the LEDs built into the prototyping board so no other hardware setup is required.
A CrossConnect JTAG interface is used to interface the host PC with the target board.
The Demo-2 application has similar functionality but tests different features of the RTOS port.
To build the application.
Also note configKERNEL_INTERRUPT_PRIORITY and configMAX_SYSCALL_INTERRUPT_PRIORITY.
See the RTOS kernel configuration documentation for full information on these configuration constants.
Attention please!: Remember that Cortex-M3 cores use numerically low priority numbers to represent HIGH
priority interrupts, which can seem counter-intuitive and is easy to forget! If you wish to assign an interrupt a low priority do NOT assign it a
priority of 0 (or other low numeric value) as this can result in the interrupt actually having the highest priority in the system - and therefore potentially make your system crash if this
priority is above configMAX_SYSCALL_INTERRUPT_PRIORITY.
The lowest priority on a Cortex-M3 core is in fact 255 - however different Cortex-M3 vendors implement a different number of priority bits and supply library
functions that expect priorities to be specified in different ways. Use the supplied examples as a reference.
Each port #defines 'BaseType_t' to equal the most efficient data type for that processor. This port defines
BaseType_t to be of type long.
Note that vPortEndScheduler() has not been implemented.
Unlike most ports, interrupt service routines that cause a context switch have no special requirements and can be written as per the compiler documentation.
The macro portEND_SWITCHING_ISR() can be used to request a context switch from within an ISR. This mechanism is demonstrated by the UART ISR defined within
main.c (see the function vUART_ISR()). Note that portEND_SWITCHING_ISR() will leave interrupts enabled.
Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.
|
Latest News
NXP tweet showing LPC5500 (ARMv8-M Cortex-M33) running FreeRTOS. Meet Richard Barry and learn about running FreeRTOS on RISC-V at FOSDEM 2019 Version 10.1.1 of the FreeRTOS kernel is available for immediate download. MIT licensed. View a recording of the "OTA Update Security and Reliability" webinar, presented by TI and AWS. Careers
FreeRTOS and other embedded software careers at AWS. FreeRTOS Partners
|