I am trying to store and retrieve a TensorflowMicro buffer array as an Arduino MBED SDRAM pointer - tensorflow

Question

The Arduino core is on github as ArduinoCore-mbed
I have had some success storing a camera buffer into Arduino MBED SDRAM, but that was fairly easy as the code was expecting a pointer when working with the camera. See code below:
SDRAMClass mySDRAM;
uint8_t *sdram_frame_buffer;
//uint8_t frame_buffer[320*320];
void setup() {
mySDRAM.begin();
sdram_frame_buffer = (uint8_t *)mySDRAM.malloc(320 * 320 * sizeof(uint8_t));
then in the main loop I did
if (cam.grab(sdram_frame_buffer) == 0){...
Note: I also do some frame alignment on the above code, but it still kind of works fine.
But now I want to store the entire TensorflowMicro c++ array
const unsigned char model_tflite[] = { 0x74, 0x69, 0x74, ...};
unsigned int model_tflite_len = 2640;
//which is later called as an array
model = tflite::GetModel(model_tflite); // name from the tflite converter model.h file
The problem here is that the Portenta has a max array size <= 1MB which is much less than the SDRAM max array size 8MB. What would be best would be to put the data for the Machine Learning model directly into SDRAM without using an array at all. Not sure if there is an easy way to do that.
Anyone have any suggestions?
Here is an example that runs on the Arduino Portenta
// Needed for SDRAM assignment on Arduino Portenta
#include <SDRAM.h>
#define ALIGN_PTR(p,a) ((p & (a-1)) ?(((uintptr_t)p + a) & ~(uintptr_t)(a-1)) : p)
SDRAMClass mySDRAM;
// assign values to a regular array
unsigned char model_tflite[] = {0x54, 0x46, 0x4c, 0x33};
unsigned int model_tflite_len = 4;
// define SDRAM pointer
unsigned char *sdram_mem;
unsigned char *sdram_tflite; // 32-byte aligned
void setup() {
Serial.begin(115200);
mySDRAM.begin(SDRAM_START_ADDRESS);
// setup SDRAM memory block
sdram_mem = (unsigned char *) SDRAM.malloc(4 + 32 /*alignment*/);
sdram_tflite = (unsigned char *)ALIGN_PTR((uintptr_t)sdram_mem, 32);
// THE PROBLEM
// How to assign the data directly to the allocated pointer memory
// without having to make an array as well
// The following traditional line works
// sdram_tflite = model_tflite;
// This line doesn't work
// sdram_tflite = {0x54, 0x46, 0x4c, 0x33};
// The following works, but is very clumsy
*(sdram_tflite + 0) = 0x54;
*(sdram_tflite + 1) = 0x46;
*(sdram_tflite + 2) = 0x4c;
*(sdram_tflite + 3) = 0x33;
}
void myShowArray( unsigned char b[], int sizeOfArray ) {
for ( int k = 0 ; k < sizeOfArray ; k++ ){
Serial.println(b[k], HEX);
}
Serial.println();
}
void myShowPointer( unsigned char *b, int sizeOfArray ) {
for ( int k = 0 ; k < sizeOfArray ; k++ ){
Serial.println(*(b + k), HEX);
}
Serial.println();
}
void loop() {
Serial.println("Regular array");
for (int i=0; i < model_tflite_len; i++){
Serial.println(model_tflite[i], HEX);
}
Serial.println();
Serial.println("SDRAM pointer as an array");
for (int i=0; i < model_tflite_len; i++){
Serial.println( *(sdram_tflite + i), HEX );
}
Serial.println();
Serial.println("Regular array passed as an array to the receiving function");
myShowArray(model_tflite, model_tflite_len);
Serial.println("Pointer passed as a pointer to the receiving function");
myShowPointer(sdram_tflite, model_tflite_len);
Serial.println("Pointer passed as an array to the receiving function");
myShowArray(*&sdram_tflite, model_tflite_len);
Serial.println("--------------------");
Serial.println();
delay(4000);
}
with output :
Regular array
54
46
4C
33
SDRAM pointer as an array
54
46
4C
33
Regular array passed as an array to the receiving function
54
46
4C
33
Pointer passed as a pointer to the receiving function
54
46
4C
33
Pointer passed as an array to the receiving function
54
46
4C
33
--------------------

Answer 1

// Needed for SDRAM assignment on Arduino Portenta
#include <SDRAM.h>
#define ALIGN_PTR(p,a) ((p & (a-1)) ?(((uintptr_t)p + a) & ~(uintptr_t)(a-1)) : p)
SDRAMClass mySDRAM;
// assign values to a regular array
unsigned char model_tflite[] = {0x54, 0x46, 0x4c, 0x33};
unsigned int model_tflite_len = 4;
// define SDRAM pointer
unsigned char *sdram_mem;
unsigned char *sdram_tflite; // 32-byte aligned
void setup() {
Serial.begin(115200);
mySDRAM.begin(SDRAM_START_ADDRESS);
// setup SDRAM memory block
sdram_mem = (unsigned char *) SDRAM.malloc(4 + 32 /*alignment*/);
sdram_tflite = (unsigned char *)ALIGN_PTR((uintptr_t)sdram_mem, 32);
// THE PROBLEM
// How to assign the data directly to the allocated pointer memory
// without having to make an array as well
// The following traditional line works
// sdram_tflite = model_tflite;
// This line doesn't work
// sdram_tflite = {0x54, 0x46, 0x4c, 0x33};
// The following works, but is very clumsy
// *(sdram_tflite + 0) = 0x54;
// *(sdram_tflite + 1) = 0x46;
// *(sdram_tflite + 2) = 0x4c;
// *(sdram_tflite + 3) = 0x33;
// Try this
// unsigned char buffer[8];
// memcpy(buffer,"\x20\x38\x00\x00\x0E\x82\x00\x06",8);
// yes this works fine!
memcpy(sdram_tflite, "\x54\x46\x4c\x33", model_tflite_len);
}
void myShowArray( unsigned char b[], int sizeOfArray ) {
for ( int k = 0 ; k < sizeOfArray ; k++ ){
Serial.println(b[k], HEX);
}
Serial.println();
}
void myShowPointer( unsigned char *b, int sizeOfArray ) {
for ( int k = 0 ; k < sizeOfArray ; k++ ){
Serial.println(*(b + k), HEX);
}
Serial.println();
}
void loop() {
Serial.println("Regular array");
for (int i=0; i < model_tflite_len; i++){
Serial.println(model_tflite[i], HEX);
}
Serial.println();
Serial.println("SDRAM pointer as an array");
for (int i=0; i < model_tflite_len; i++){
Serial.println( *(sdram_tflite + i), HEX );
}
Serial.println();
Serial.println("Regular array passed as an array to the receiving function");
myShowArray(model_tflite, model_tflite_len);
Serial.println("Pointer passed as a pointer to the receiving function");
myShowPointer(sdram_tflite, model_tflite_len);
Serial.println("Pointer passed as an array to the receiving function");
// myShowArray(*&sdram_tflite, model_tflite_len);
myShowArray(sdram_tflite, model_tflite_len);
Serial.println("--------------------");
Serial.println();
delay(4000);
}