tmedicci opened a new pull request, #15825:
URL: https://github.com/apache/nuttx/pull/15825
## Summary
<!-- This field should contain a summary of the changes. It will be
pre-filled with the commit's message and descriptions. Adjust it accordingly -->
* xtensa/esp32s3: allow moving .bss data to the external PSRAM
This commit allows placing .bss data into the external PSRAM. Previously,
the PSRAM was fully allocated to the heap memory only
and now part of it can be used to allocate .bss data freeing the internal
memory.
## Impact
<!-- Please fill the following sections with YES/NO and provide a brief
explanation -->
Impact on user: YES. User's application that set `__attribute__ ((section
(".ext_ram.bss")))` for a static variable will allocate it to the external
PSRAM (freeing the internal memory).
Impact on build: NO. It doesn't break any existing build
Impact on hardware: YES. This allows non-initialized data (`.bss`) to be
allocated in the external PSRAM of ESP32-S3, freeing the internal memory.
Impact on documentation: NO.
Impact on security: NO.
Impact on compatibility: NO.
## Testing
It can be simply tested by setting the `__attribute__ ((section
(".ext_ram.bss")))` attribute to a static variable. Please consider the
following patch that adds it to the hello world app of `nuttx-apps`:
```
diff --git a/examples/hello/hello_main.c b/examples/hello/hello_main.c
index fd194a623a..4f9b6f6a28 100644
--- a/examples/hello/hello_main.c
+++ b/examples/hello/hello_main.c
@@ -27,6 +27,9 @@
#include <nuttx/config.h>
#include <stdio.h>
+static int data_bss[1024];
+__attribute__ ((section (".ext_ram.bss"))) static int data_bss_ext[1024];
+
/****************************************************************************
* Public Functions
****************************************************************************/
@@ -38,5 +41,7 @@
int main(int argc, FAR char *argv[])
{
printf("Hello, World!!\n");
+ printf("data_bss: %p\n", (void *)data_bss);
+ printf("data_bss_ext: %p\n", (void *)data_bss_ext);
return 0;
}
```
### Building
After applying the patch, one can build and flash it on ESP32-S3:
```
$ make -j distclean && ./tools/configure.sh esp32s3-devkit:nsh &&
kconfig-tweak -e EXAMPLES_HELLO && make olddefconfig && make flash
EXTRAFLAGS="-Wno-cpp -Werror" ESPTOOL_PORT=/dev/ttyUSB0 -s -j$(nproc) && minicom
```
### Running
On NSH:
```
nsh> hello
Hello, World!!
data_bss: 0x3fc8a758
data_bss_ext: 0x3c050000
nsh>
```
### Results
The memory address is consistent with ESP32-S3's
[TRM](https://www.espressif.com/sites/default/files/documentation/esp32-s3_technical_reference_manual_en.pdf)
(figure 4.2-1):
The variable that had the attribute set (`data_bss_ext`) is allocated to the
external memory (PSRAM) while the `data_bss` refers to the internal memory.
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