FreeRTOS Demo for the NEORV32 Processor

This example shows how to run FreeRTOS on the NEORV32 processor. It features the default "blinky_demo" and the more sophisticated "full_demo" demo applications. See the comments in main.c and the according source files for more information.

The chip-specific extensions folder (chip_specific_extensions/neorv32) should be in $(FREERTOS_HOME)/Source/portable/GCC/RISC-V/chip_specific_extensions, but is placed in this source directory for simplicity.

ℹ️ Tested with FreeRTOS version V10.4.4+

Requirements

Hardware
- DMEM/IMEM requirements depend on the actual application (for example: 16kB DMEM and 16kB IMEM for "blinky_demo")
- peripherals: MTIME (machine timer), UART0, GPIO
- CPU ISA extensions: Zicsr
Software
- NEORV32 software framework
- RISC-V gcc
- FreeRTOS
- application-specific configuration of FreeRTOSConfig.h (especially configCPU_CLOCK_HZ)
- application-specific configuration of the NEORV32 linker script when using non-default IMEM or DMEM configurations (size!)

Instructions

Download FreeRTOS from the official GitHub repository or from the its official homepage.

$ git clone https://github.com/FreeRTOS/FreeRTOS.git

Open the makefile from this example folder and configure the FREERTOS_HOME variable to point to your FreeRTOS home folder.

FREERTOS_HOME ?= /mnt/n/Projects/FreeRTOSv10.4.1

Compile the NEORV32 executable. Do not forget the RUN_FREERTOS_DEMO switch.

$ make USER_FLAGS+=-DRUN_FREERTOS_DEMO clean_all exe

Note: The *.c sources and the FreeRTOS-specific part of the makefile have (include) guards that test if RUN_FREERTOS_DEMO is defined. This has no practical usage for the user - it is just a work-around for the NEORV32 CI environment.

Upload the executable (neorv32_exe.bin) to the processor via the bootloader and execute it.

CMD:> u
Awaiting neorv32_exe.bin... OK
CMD:> e
Booting...

FreeRTOS V10.4.4+ on NEORV32 Demo

Blink
Blink
Blink
Blink

FreeRTOS Plus

To automatically add source and include files from FreeRTOS plus extensions add one (or more) of the following arguments when invoking make:

FreeRTOS-Plus-CLI: USER_FLAGS+=-FREERTOS_PLUS_CLI
FreeRTOS-Plus-TCP: USER_FLAGS+=-FREERTOS_PLUS_TCP

Example:

$ make USER_FLAGS+=-DRUN_FREERTOS_DEMO USER_FLAGS+=-FREERTOS_PLUS_TCP clean_all exe

NEORV32-Specific Interrupts and Exceptions

The main.c file provides two "trampolines" for NEORV32-specific interrupts/exceptions:

/* Handle NEORV32-specific interrupts */
void freertos_risc_v_application_interrupt_handler(void) {

  // acknowledge/clear ALL pending interrupt sources
  neorv32_cpu_csr_write(CSR_MIP, 0);

  // debug output
  neorv32_uart0_printf("\n<NEORV32-IRQ> mcause = 0x%x </NEORV32-IRQ>\n", neorv32_cpu_csr_read(CSR_MCAUSE));
}

/* Handle NEORV32-specific exceptions */
void freertos_risc_v_application_exception_handler(void) {

  // debug output
  neorv32_uart0_printf("\n<NEORV32-EXC> mcause = 0x%x </NEORV32-EXC>\n", neorv32_cpu_csr_read(CSR_MCAUSE));
}

This functions can be used to call specific handlers based on the value from the mcause CSR, which indicates the actual cause of the interrupt or exception (for example FIRQ channel or illegal instruction).

Notes

The onfiguration of the FreeRTOS home folder (via FREERTOS_HOME) is corrupted if the compiler shows the following error:

main.c:36:10: fatal error: FreeRTOS.h: No such file or directory
   36 | #include <FreeRTOS.h>
      |          ^~~~~~~~~~~~
compilation terminated.
make: *** [makefile:203: main.c.o] Error 1

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