Table of Contents

CLR Managed heap definition

About this document

This document describes how the CLR manged heap is defined as a ChibiOS target.

For STM32 based devices: The configurations are chained by linker files:

  • the target linker file provided for the nanoCLR in the target board folder, e.g. STM32F091xC.ld and from within calls rules.ld except the F7 series which calls rules_clr.ld, rules_code.ld, rules_data.ld and rules_stacks.ld directly.
  • rules.ld (which is common to all STM32 based ChibiOS targets and calls the next set of linker files)
  • rules_clr.ld, rules_code.ld, rules_data.ld and rules_stacks.ld

Managed heap location and size

The CLR managed heap can be located on the target board at any RAM address where space available. Either internal or external.

It will be placed (considering the RAM region defined) after the region containing the CRT heap (if it's assigned to that same RAM region) and right before the Vector table copy in RAM (if it is assigned to the same RAM region).

This empowers developers to create new target boards with maximum flexibility of where to locate the CLR managed heap and its respective size.

Definition the CLR managed heap location

The location of the CLR managed heap is set in in target linker file provided for nanoCLR in the target boards folder, e.g. STM32F091xC_CLR.ld

For example the line (usually toward the end of the file) will contain something similar to REGION_ALIAS("CLR_MANAGED_HEAP_RAM", ram0);. The example stated here defines CLR manged heap location as being set in the ram0 region. The RAM regions and respective sizes are defined in the same file. For further information, please check the ChibiOS documentation for details on how to define further RAM regions.

Size of the CLR managed heap

The size of the CLR managed heap is automatically adjusted to take all the available RAM space after the CRT heap (if it's assigned to that same RAM region).

It maybe be required to adjust the size of the CRT heap. This is set in the CMake file of the target board, e.g. CMakeLists.txt. Look for the __crt_heap_size__ definition in a line that contain something similar to --defsym=__crt_heap_size__=0x800. In the example stated here the size of CRT heap is being set to 0x800.

When defining the size you need to take into account several factors:

  • the total available size of the region where it's being placed
  • if there are initialized variables assigned to this region how much space they are taking
  • if the CRT heap is located in this region and the size left for it is enough

The linker is only able to determine whether there is enough room for all of these factors and it will only complain if there isn't. However it can not determine if the CRT heap (just like the CRT heap) is large enough for the running requirements. That is up to the target board developer. For a detailed overview on the final memory map you may want to check the nanoCLR.map that will be located in the build folder after a successful build. Look for the regions called .heap and .clr_managed_heap to see the final addresses where those were placed.

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