Compiler optimizations and memcpy - c++

Question

I have an Arduino Pro Mini and an ESP32 connected by SPI. Arduino should make packets and send them to the ESP32 and vice versa.
Here are sketch for Arduino:
#include <stdint.h>
#include <time.h>
#include "SPI.h"
#define ChipSelect 10
#define Handshake 14
#define FF_PACKET_FIXED_LENGTH 5
#define SPI_BUFFER_SIZE 128
static const uint16_t crc16_table[256] = {
0x0000,0xC0C1,0xC181,0x0140,0xC301,0x03C0,0x0280,0xC241,
0xC601,0x06C0,0x0780,0xC741,0x0500,0xC5C1,0xC481,0x0440,
0xCC01,0x0CC0,0x0D80,0xCD41,0x0F00,0xCFC1,0xCE81,0x0E40,
0x0A00,0xCAC1,0xCB81,0x0B40,0xC901,0x09C0,0x0880,0xC841,
0xD801,0x18C0,0x1980,0xD941,0x1B00,0xDBC1,0xDA81,0x1A40,
0x1E00,0xDEC1,0xDF81,0x1F40,0xDD01,0x1DC0,0x1C80,0xDC41,
0x1400,0xD4C1,0xD581,0x1540,0xD701,0x17C0,0x1680,0xD641,
0xD201,0x12C0,0x1380,0xD341,0x1100,0xD1C1,0xD081,0x1040,
0xF001,0x30C0,0x3180,0xF141,0x3300,0xF3C1,0xF281,0x3240,
0x3600,0xF6C1,0xF781,0x3740,0xF501,0x35C0,0x3480,0xF441,
0x3C00,0xFCC1,0xFD81,0x3D40,0xFF01,0x3FC0,0x3E80,0xFE41,
0xFA01,0x3AC0,0x3B80,0xFB41,0x3900,0xF9C1,0xF881,0x3840,
0x2800,0xE8C1,0xE981,0x2940,0xEB01,0x2BC0,0x2A80,0xEA41,
0xEE01,0x2EC0,0x2F80,0xEF41,0x2D00,0xEDC1,0xEC81,0x2C40,
0xE401,0x24C0,0x2580,0xE541,0x2700,0xE7C1,0xE681,0x2640,
0x2200,0xE2C1,0xE381,0x2340,0xE101,0x21C0,0x2080,0xE041,
0xA001,0x60C0,0x6180,0xA141,0x6300,0xA3C1,0xA281,0x6240,
0x6600,0xA6C1,0xA781,0x6740,0xA501,0x65C0,0x6480,0xA441,
0x6C00,0xACC1,0xAD81,0x6D40,0xAF01,0x6FC0,0x6E80,0xAE41,
0xAA01,0x6AC0,0x6B80,0xAB41,0x6900,0xA9C1,0xA881,0x6840,
0x7800,0xB8C1,0xB981,0x7940,0xBB01,0x7BC0,0x7A80,0xBA41,
0xBE01,0x7EC0,0x7F80,0xBF41,0x7D00,0xBDC1,0xBC81,0x7C40,
0xB401,0x74C0,0x7580,0xB541,0x7700,0xB7C1,0xB681,0x7640,
0x7200,0xB2C1,0xB381,0x7340,0xB101,0x71C0,0x7080,0xB041,
0x5000,0x90C1,0x9181,0x5140,0x9301,0x53C0,0x5280,0x9241,
0x9601,0x56C0,0x5780,0x9741,0x5500,0x95C1,0x9481,0x5440,
0x9C01,0x5CC0,0x5D80,0x9D41,0x5F00,0x9FC1,0x9E81,0x5E40,
0x5A00,0x9AC1,0x9B81,0x5B40,0x9901,0x59C0,0x5880,0x9841,
0x8801,0x48C0,0x4980,0x8941,0x4B00,0x8BC1,0x8A81,0x4A40,
0x4E00,0x8EC1,0x8F81,0x4F40,0x8D01,0x4DC0,0x4C80,0x8C41,
0x4400,0x84C1,0x8581,0x4540,0x8701,0x47C0,0x4680,0x8641,
0x8201,0x42C0,0x4380,0x8341,0x4100,0x81C1,0x8081,0x4040};
// Вычисление контрольной суммы
uint16_t ffCrc16(const uint8_t *data, uint16_t data_size) {
if (!data || !data_size) {
return 0;
}
uint16_t crc = 0;
uint8_t *buf = (uint8_t *) data;
while (data_size--) {
crc = (crc >> 8) ^ crc16_table[(uint8_t)crc ^ *buf++];
}
return crc;
}
// the setup function runs once when you press reset or power the board
void setup() {
Serial.begin(9600);
// set the CipSelectPin & LED as an output:
pinMode(ChipSelect, OUTPUT);
pinMode(LED_BUILTIN, OUTPUT);
// initialize digital pin Handsake as an input.
pinMode(Handshake, INPUT);
Serial.println("Test ESP-32");
// initialize SPI:
SPI.begin();
Serial.println("SPI Init");
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
delay(1000); // wait for a second
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
delay(1000); // wait for a second
}
void loop() {
Serial.println("===== Loop iter start =====");
uint8_t data[50] = {0};
uint8_t *dataPtr = data;
Serial.print("sizeof(data) = ");
Serial.println(sizeof(data));
Serial.print("sizeof(dataPtr) = ");
Serial.println(sizeof(dataPtr));
uint32_t val = 1;
Serial.print("sizeof(val) = ");
Serial.println(sizeof(val));
memcpy(dataPtr, &val, 4);
dataPtr += 4;
val = (uint32_t) time(NULL);
memcpy(dataPtr, &val, 4);
dataPtr += 4;
val = 1;
memcpy(dataPtr, &val, 1);
dataPtr += 1;
val = 15;
memcpy(dataPtr, &val, 4);
dataPtr += 4;
Serial.print("data: ");
printPacket(data, 13);
uint8_t packet[50] = {0};
uint16_t packetSize = 50;
Serial.print("sizeof(packet) = ");
Serial.println(sizeof(packet));
Serial.print("sizeof(packetSize) = ");
Serial.println(sizeof(packetSize));
ffCreateCustomPacket(0xA0, data, 13, packet, &packetSize);
if (packetSize > 0) {
ffSendPacket(packet, packetSize);
}
Serial.println("===== Loop iter end =====");
delay(20000);
}
void printPacket(uint8_t *packet, uint16_t packetSize) {
uint32_t dumpSize = packetSize * 2;
char hexDump[dumpSize];
char *p = hexDump;
memset(hexDump, 0, dumpSize);
for (uint16_t i = 0; i < packetSize; ++i) {
sprintf(p, "%02x", packet[i]);
p += 2;
}
Serial.println(hexDump);
}
void ffCreateCustomPacket(uint8_t signature, uint8_t *data, uint16_t dataSize, uint8_t *buf, uint16_t *bufSize) {
uint16_t packetSize = FF_PACKET_FIXED_LENGTH + dataSize;
if (*bufSize < packetSize) {
Serial.println("Not enough buffer size!");
*bufSize = 0;
return;
}
Serial.print("data2: ");
printPacket(data, dataSize);
uint8_t *packetStart = buf;
// signature
*buf = signature;
buf++;
Serial.print("signature: ");
printPacket(packetStart, 50);
// dataSize
memcpy(buf, &dataSize, 2);
buf += 2;
Serial.print("size: ");
printPacket(packetStart, 50);
Serial.print("dataSize = ");
Serial.println(dataSize);
// data
memcpy(buf, data, dataSize);
buf += dataSize;
Serial.print("data: ");
printPacket(packetStart, 50);
// CRC
uint16_t crc = ffCrc16(packetStart, packetSize - 2);
memcpy(buf, &crc, 2);
buf += 2;
*bufSize = packetSize;
Serial.print("packet: ");
printPacket(packetStart, 50);
}
void ffSendPacket(uint8_t *packet, uint16_t packetSize) {
Serial.print("Send packet: ");
printPacket(packet, packetSize);
uint8_t spiBuffer[SPI_BUFFER_SIZE] = {0};
memcpy(spiBuffer, packet, packetSize);
SPI.transfer(spiBuffer, SPI_BUFFER_SIZE);
Serial.print("Received: ");
printPacket(spiBuffer, SPI_BUFFER_SIZE);
}
Here's the log output:
sizeof(data) = 50
sizeof(dataPtr) = 2
sizeof(val) = 4
data: 0100000000000000010f000000
sizeof(packet) = 50
sizeof(packetSize) = 2
data2: 0100000000000000010f000000
signature: a0000000000000000000000000...
size: a00d0000000000000000000000...
dataSize = 13
data: a00d0000000000000000000000...
packet: a00d0000000000000000000000000000b57d...
Send packet: a00d0000000000000000000000000000b57d
Received: 000...
Loop iter end
Actual packet should be a00d000100000000000000010f000000xxxx (xxxx - crc), but I get a00d0000000000000000000000000000b57d.
If I switch compiler flags from Os to O0 everything works fine. Are there some optimizations that cut off data memcpy and how to tell compiler not to do that?
Additional info: if I make packet array as static or allocate it on heap all works as expected too.