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Normally, statically allocated data goes in .bss, followed by the
initial stack, followed by HEAP. However, any data that is statically
allocated in SRAM4 with __attribute__ ((section (".sram4"))) will
clobber, and be clobbered by, the HEAP.
On STM32H7, BDMA can only access SRAM4. Therefore any BDMA buffers (or
any other data) placed in SRAM4 will expose this problem. In one case,
this manifested as a failure of NSH to start, because the SPI6 BDMA
buffers clobbered the /dev/console inode structs, which the OS
allocated earlier.
This PR ensures that only the rest of SRAM4, after any static data, is
added to the heap. This PR also allows SRAM4 to be completely excluded
from the heap by a new Kconfig, CONFIG_STM32H7_SRAM4EXCLUDE, similar
to what CONFIG_STM32H7_DTCMEXCLUDE does for the DTCM region.
Change required in linker scripts:
Every STM32H7 linker script must replace this:
.sram4 :
{
} > sram4
with this:
.sram4_reserve (NOLOAD) :
{
*(.sram4)
. = ALIGN(4);
_sram4_heap_start = ABSOLUTE(.);
} > sram4
or link will fail with: undefined reference to '_sram4_heap_start'.
The Release Notes should document this for users with out-of-tree
boards.
arch/arm/src/stm32h7/Kconfig:
* Add config STM32H7_SRAM4EXCLUDE to allow excluding all of SRAM4
from the HEAP.
arch/arm/src/stm32h7/stm32_allocateheap.c:
* Only when including SRAM4 in the heap, define HAVE_SRAM4,
SRAM4_START, SRAM4_END, and SRAM4_HEAP_START.
* Add "Private Data" section.
* Add extern for_sram4_heap_start, which must be defined in the
board's linker script.
* arm_addregion(): Only add SRAM4 to the heap when configured to
do so, i.e., unless CONFIG_STM32H7_SRAM4EXCLUDE is defined, and
only add the portion of SRAM4 that is past any static data.
boards/arm/stm32h7/nucleo-h743zi/scripts/flash.ld:
boards/arm/stm32h7/nucleo-h743zi/scripts/kernel.space.ld:
boards/arm/stm32h7/nucleo-h743zi2/scripts/flash.ld:
boards/arm/stm32h7/stm32h747i-disco/scripts/flash.ld:
boards/arm/stm32h7/stm32h747i-disco/scripts/kernel.space.ld:
* Update all in-tree STM32H7 board linker scripts as described in
"Change required in linker scripts" above.
Testing:
* Successfully built all of the following configurations:
nucleo-h743zi2:jumbo
nucleo-h743zi2:nsh
nucleo-h743zi:nxlines_oled
nucleo-h743zi:elf
nucleo-h743zi:otg_fs_host
nucleo-h743zi:nsh
nucleo-h743zi:netnsh
nucleo-h743zi:pwm
stm32h747i-disco:nsh
* Tested with custom board.
* nxstyle.
References:
[1] See the dev@nuttx.a.o mailing list discussion started 2021/03/25:
"How to ensure HEAP will not overlap static DMA buffer?"
https://lists.apache.org/thread.html/recf2bb9043f8c9f53c10917e2adb2ec64fe35dc5e6f9a695a7ac6ecc%40%3Cdev.nuttx.apache.org%3E
[2] See arm_addregion() in arch/arm/src/stm32h7/stm32_allocateheap.c
Thanks to Gregory Nutt and David Sidrane for suggestions and reviews.
The maximum number of samples which can be handled without overrun depends on various factors.
This is the user's responsibility to correctly select this value.
Since the interfece to update the sampling time is available for all supported devices,
the user can change the default vaules in the board initialization logic and avoid ADC overrun.
