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Configuration of Chibios, HAL and MCU

For a successful build the following changes are required:

In halconf.g (in both nanoBooter and nanoCLR folders), when compared with a default file:

  • HAL_USE_SERIAL to TRUE
  • SERIAL_DEFAULT_BITRATE to 921600
  • SERIAL_BUFFERS_SIZE has to be at least 64 (2x the Wire Protocol packet size) otherwise the transmission will be garbled as the packets overrun each other

In mcuconf.h (in both nanoBooter and nanoCLR folders), when compared with a default file:

  • STM32_SERIAL_USE_USART2 to TRUE

Definitions for each image

Any defines specific to an image (nanoBooter or nanoCLR) that are to be made available throughout the code should be added to the target_board.h.in. There is one in nanoBooter and another in nanoCLR directories, allowing different defines for each one. Defines that are common to a target board should be added to the target_common.h.in. The content of these files is parsed by CMake. It can include CMake variables. Check the documentation of CMake config files here.

nanoCLR image start address

The start address of nanoCLR (it's vector table) is defined in the linker file (STM32F091xC.ld)[nanoCLR/STM32F091xC.ld] by setting the initial address of the flash region. The total size has to be the flash region size less the space reserved for nanoBooter.

Vector table copy to RAM

Because the STM32F0 series don't have the SCB->VTOR register that allows offsetting the vector table another approach as to be taken: copy the vector table to a RAM location and remap the memory mode using SYSCFG->CFGR1. This is accomplished by reserving in RAM0 region the required space (in the linker file) and by performing the copy of the vector table right after the nanoCLR starts. This code block is located in main() right after the call to halInit().

If porting this reference board to another STM32F0 (or L0) series make sure this piece of code is kept there.

NOTE: this configuration was successfully tested in a NUCLEO_F091RC board using the virtual COM port through the ST Link USB connection.

Floating point

The current build is set to add support for single-precision floating point. Meaning that System.Math API supports only the float overloads. The double ones will throw a NotImplementedException. There is no FPU available, so floating point is provided through software implementation.