Arduino GIGA SDRAM as shared memory

Official Hardware Mega GIGA R1 WiFi
1

Hi,
I am struggling for few days to find solution and explanation for weird beahviour (so, posted code is trying basic stuff). When I malloc memory in SDRAM for string in CM7, which I want to modify in CM4 core, data which CM4 see are different. I've added cache clearing and invalidating, but no luck with solving this - does anyone have any ideas?

Thanks :slight_smile:

Code CM7:

#include <SDRAM.h>
#include <RPC.h>

#define BUFF_SIZE 128
#define BUFF_TEXT "Toto je nouzove volani o pomoc lodi Jupiterske dulni spolecnosti Cerveny trpaslik"
char *sdram_text;

void setup()
{
  Serial.begin(115200);
  while (!Serial);

  RPC.begin();
  SDRAM.begin();

  sdram_text = (char*)SDRAM.malloc(BUFF_SIZE);
  Serial.println((uint32_t)sdram_text, HEX);
  memset(sdram_text, '\0', BUFF_SIZE);
  strcpy(sdram_text, BUFF_TEXT);

  SCB_CleanDCache();

  Serial.print("Text: |");
  Serial.print(sdram_text);
  Serial.println("|");

  delay(1000); //delay 
  RPC.call("modify_buffer", (uint32_t)sdram_text, 32);
  delay(1000); //delay 
  
  SCB_InvalidateDCache_by_Addr(sdram_text, 4);
  Serial.print("Text po zpracovani: |");
  Serial.print(sdram_text);
  Serial.println("|");

  Serial.println("==========================");
}

String b = "";

void loop()
{
  while (RPC.available())
    b += (char)RPC.read();

  if (b[b.length()-1] == '\n')
  {
    Serial.println(b);
    b = "";
  }
}

Code CM4:

#include <SDRAM.h>
#include <RPC.h>

void setup() {
  RPC.begin();
  RPC.bind("modify_buffer", modify_buffer);
}

void modify_buffer(uint32_t pointer, uint32_t len)
{
  char *p = (char*)pointer;

  RPC.println(p);

}

void loop() {}

Data being received in CM4 (I've used RPC.println to get them back):
Totj je nouvove volini o pococ lodiuJupitereke dulns spolecsosti Ceeveny trsaslik

Is there a M4 and M7 Usage for dummies document :D
2

No ideas? :open_mouth:

3

have you tried using a fixed memory location such as the beginning of SDRAM4 space at 0X38000000?

4

As a try:

Before the RPC.call() add:

SCB_CleanInvalidateDCache_by_Addr(sdram_text, BUFF_SIZE);

Or change SCB_CleanDCache() to SCB_CleanInvalidateDCache()

5

Trying to use SDRAM as shared memory between M7 and M4, I get the same problem : chars can be wrong when exchanged between M7 and M4 through read/write.

The problem is even worse : M4 can't read correctly what it writes in the SDRAM !

This excludes a cache managment problem.

To understand and localize the dysfunction (and try to find a solution) I searched in the files around SDRAM and in SDRAM.cpp (yes, it was easy) found a "beautiful" test checking if the SDRAM is working fine or not :

bool __attribute__((optimize("O0"))) SDRAMClass::test(bool fast, Stream& _serial)

When executed on the M7 core, no problemo !

On the M7 :

#include <Wire.h>
#include <RPC.h>
#include <SDRAM.h>

void setup()
{
  int i;

// Ouverture de la liaison série via USB-C
  Serial.begin(115200);

  delay(1000);

//  Initialisation SDRAM
  SDRAM.begin();

  Serial.println("M7: test SDRAM...");
  SDRAM.test(false,Serial);
  Serial.println("M7: test SDRAM done");

// M4 launch
  RPC.begin();
}

// Main loop

void loop()
{
  while(RPC.available())
    Serial.write(RPC.read());
}

On the M4 :

#include <RPC.h>
#include <SDRAM.h>

//
// Initialisation
//

void setup()
{
//  Initialisation des RPC
    RPC.begin();

//  Initialisation SDRAM
    SDRAM.begin();

    RPC.println("M4: test SDRAM...");
    SDRAM.test(false,RPC);
    RPC.println("M4: test SDRAM done");
}

// Main loop

void loop()
{
}

And the output is :

M7: test SDRAM...
M7: test SDRAM done
M4: test SDRAM...
address bus test failed! address (60000007)

and the GIGA R1 is stopped ( __asm__ volatile ("BKPT"); called in the test method).

I don't know if it 's only my card who has a hardware bug between the M4 and the SDRAM or if it's always the case, but the only solution for me is to use regular RAM between the cores.

In a nutshell : Only the M7 core can use the 8MB of SDRAM.