RPi Wiringpi fails to read i2c correctly - raspberry-pi

Question

I have an AHT21 that communicates over i2c: I send 3 bytes and get back 6. The arduino sketch works but the RPi does not. What is wrong with WiringPi i2c syntax?
I want to convert this arduino sketch to RPi c++ program using WiringPi.
This works:
#include <Wire.h>
#define AHT21 0x38
void setup() {
// put your setup code here, to run once:
Wire.begin(); // the SDA and SCL
Serial.begin(9600);
uint8_t rawData[7] = {0,0,0,0,0,0,0};
Wire.beginTransmission(AHT21);
Wire.write(0xAC); //send measurement command, start measurement
Wire.write(0x33); //send measurement control
Wire.write(0x00); //send measurement NOP control
Wire.endTransmission();
delay(100);
Wire.requestFrom(AHT21, 6);
for (uint8_t i = 0; i < 6; i++)
{
rawData[i] = Wire.read();
Serial.print(i);Serial.print(": ");
Serial.println(rawData[i]);
}
}
void loop() {}
Gives:
0: 28
1: 106
2: 90
3: 117
4: 126
5: 70
This RPI code fails giving the status byte over and over:
#include <wiringPi.h>
#include <wiringPiI2C.h>
#include <stdio.h>
#include <stdint.h>
#include <math.h>
#define Address 0x38
int main (int argc, char **argv)
{
int fd = wiringPiI2CSetup(Address);
uint8_t rawData[7] = {0,0,0,0,0,0,0};
wiringPiI2CWrite(fd,0xAC); //send measurement command, start measurement
wiringPiI2CWrite(fd,0x33); //send measurement control
wiringPiI2CWrite(fd,0x00); //send measurement NOP control
delay(100);
for (uint8_t i = 0; i < 6; i++)
{
rawData[i] = wiringPiI2CRead(fd);
printf("%d: %d\n",i,rawData[i]);
}
}
Gives:
./aht21
0: 28
1: 28
2: 28
3: 28
4: 28
5: 28

Answer 1

I abandoned WiringPi and went with ioctl and i2c-dev.h. Works fine:
//gcc -g -Wall -Wextra -pedantic -std=c11 -D_DEFAULT_SOURCE -D_BSD_SOURCE -o aht21 aht21.c
#include <stdio.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h> // read/write usleep
#include <stdlib.h> // exit function
#include <inttypes.h> // uint8_t, etc
#include <linux/i2c-dev.h> // I2C bus definitions
int main (int argc, char **argv)
{
float ahtTemp, ahtHum;
uint8_t rawData[7] = {0, 0, 0, 0, 0, 0, 0};
// Create I2C bus
int fd;
char *bus = "/dev/i2c-1";
if ((fd = open(bus, O_RDWR)) < 0)
{
printf("Failed to open the bus. \n");
exit(1);
}
// Get I2C device,
ioctl(fd, I2C_SLAVE, 0x38);
char TriggerCMD[3] = {0};
TriggerCMD[0] = 0xAC;
TriggerCMD[1] = 0x33;
TriggerCMD[2] = 0x00;
write(fd, TriggerCMD, 3);
sleep(1);
if (read(fd, rawData, 7) != 7)
{
printf("Error : Input/Output Error \n");
}
else
{
uint32_t humidity = rawData[1]; //20-bit raw humidity data
humidity <<= 8;
humidity |= rawData[2];
humidity <<= 4;
humidity |= rawData[3] >> 4;
uint32_t temperature = rawData[3] & 0x0F; //20-bit raw temperature data
temperature <<= 8;
temperature |= rawData[4];
temperature <<= 8;
temperature |= rawData[5];
ahtHum = ((float)humidity / 0x100000) * 100.0;
ahtTemp = (((float)temperature / 0x100000) * 200.0 - 50.0) * 1.8 + 32.0;
printf("%.2f,%.2f\n", ahtHum, ahtTemp);
}
close(fd);
}