DRAM segment data does not fit?

[Greg Corson]

Hi,
I have some fairly simple Arduino code that is allocating a couple of buffer structures like this:

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typedef struct
{
  int len;
  uint8_t buff[INTERRUPT_BUFFER_SIZE];
} Buffer, *Buffer_ptr;

Buffer
  bufferA,
  bufferB;

When INTERRUPT_BUFFER_SIZE is 42000 I get the following info from the compile which seems to be saying I have a lot of memory left.

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Sketch uses 700270 bytes (53%) of program storage space. Maximum is 1310720 bytes.
Global variables use 123436 bytes (37%) of dynamic memory, leaving 204244 bytes for local variables. Maximum is 327680 bytes.

When INTERRUPT_BUFFER_SIZE is 43000 I get this error.

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c:/users/gcorson/appdata/local/arduino15/packages/esp32/tools/xtensa-esp32-elf-gcc/1.22.0-80-g6c4433a-5.2.0/bin/../lib/gcc/xtensa-esp32-elf/5.2.0/../../../../xtensa-esp32-elf/bin/ld.exe: C:\Users\gcorson\AppData\Local\Temp\1\arduino_build_508386/SPI_IMU_Test_Telemetry.ino.elf section `.dram0.bss' will not fit in region `dram0_0_seg'

c:/users/gcorson/appdata/local/arduino15/packages/esp32/tools/xtensa-esp32-elf-gcc/1.22.0-80-g6c4433a-5.2.0/bin/../lib/gcc/xtensa-esp32-elf/5.2.0/../../../../xtensa-esp32-elf/bin/ld.exe: DRAM segment data does not fit.

c:/users/gcorson/appdata/local/arduino15/packages/esp32/tools/xtensa-esp32-elf-gcc/1.22.0-80-g6c4433a-5.2.0/bin/../lib/gcc/xtensa-esp32-elf/5.2.0/../../../../xtensa-esp32-elf/bin/ld.exe: region `dram0_0_seg' overflowed by 864 bytes

collect2.exe: error: ld returned 1 exit status

I don't understand this, at 42000 it says I have 204244 bytes free, why does adding another 20k bytes make it too big? Is there a way to let me use more memory?

[ESP_Angus]

ESP-IDF currently has a statically allocated memory limit of 160KB. The remaining DRAM has to be allocated dynamically.

You can modify your code to allocate this large buffer dynamically at runtime, and it should work:

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Buffer *bufferA;
Buffer *bufferB;

void setup() {
  bufferA = new Buffer();
  bufferB = new Buffer();
}

... and then use "bufferA->field" anywhere you previously had "bufferA.field".

A GitHub issue was recently opened about the same underlying problem. If you have a GitHub account you can subscribe to receive an update when it's fixed: https://github.com/espressif/esp-idf/issues/3497

[Greg Corson]

Thanks! I'll give this a try.

It's an easy change because these were ping-pong buffers and are already referenced through pointers everywhere else in the code.