davids5 commented on a change in pull request #459: stm32h7: support SDRAM via
FMC peripherial
URL: https://github.com/apache/incubator-nuttx/pull/459#discussion_r397833561
##########
File path: arch/arm/src/stm32h7/stm32_allocateheap.c
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@@ -60,33 +60,57 @@
#include "hardware/stm32_memorymap.h"
#include "stm32_mpuinit.h"
#include "stm32_dtcm.h"
+#include "stm32_fmc.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
-/* Internal SRAM is available in all members of the STM32 family. The
- * following definitions must be provided to specify the size and
- * location of internal(system) SRAM:
+/* At startup the kernel will invoke up_addregion() so that platform code
+ * may register available memories for use as part of system heap.
+ * The global configuration option CONFIG_MM_REGIONS defines the maximal
+ * number of non-contiguous memory ranges that may be registered with the
+ * system heap. You must make sure it is large enough to hold all memory
+ * regions you intend to use.
*
- * In addition to internal SRAM, external RAM may also be available through
- * the FMC. In order to use FMC RAM, the following additional things need
- * to be present in the NuttX configuration file:
+ * The following memory types can be used for heap on STM32H7 platform:
*
- * CONFIG_STM32H7_FMC=y : Enables the FMC
- * CONFIG_STM32H7_FMC_S[D]RAM=y : SRAM and/or SDRAM is available via the FMC.
- * Either of these autoselects
- * CONFIG_ARCH_HAVE_HEAP2 which is what we
- * are interested in here.
- * CONFIG_HEAP2_BASE : The base address of the external RAM in
- * the FMC address space
- * CONFIG_HEAP2_SIZE : The size of the external RAM in the FMC
- * address space
- * CONFIG_MM_REGIONS : Must be set to a large enough value to
- * include the FMC external RAM (as determined
- * by the rules provided below)
+ * - AXI SRAM is a 512kb memory area. This will be automatically registered
+ * with the system heap in up_allocate_heap, all the other memory
+ * regions will be registered in up_addregion().
+ * So, CONFIG_MM_REGIONS must be at least 1 to use AXI SRAM.
*
- * CONFIG_STM32H7_DTCMEXCLUDE : Set to exclude the DTCM from heap
+ * - Internal SRAM is available in all members of the STM32 family.
+ * This is always registered with system heap.
+ * There are two contiguous regions of internal SRAM:
+ * SRAM1+SRAM2+SRAM3 and SRAM4 at a separate address.
+ * So, add 2 more to CONFIG_MM_REGIONS.
+ *
+ * - Tightly Coupled Memory (TCM RAM), we can use Data TCM (DTCM) for system
+ * heap. Note that DTCM has a number of limitations, for example DMA
+ * transfers to/from DTCM are impossible.
Review comment:
```suggestion
* transfers to/from DTCM are limited.
```
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