How do I send multiple 32 byte strings to I2C master? - arduino

Question

I have multiple variable length strings which do not exceed 32 bytes each which need to be sent via I2C between 2 Arduino Nanos. I use # to terminate each string. I can successfully send and receive the first string, but for the life of me I can't figure out how to send the succeeding strings. The samples I am testing with look like this:
String answer = "12345,123.4,50.6,12345#";
String answerV = "4.10,4.15,4.13,4.05,4.18,0#";
Master Code
#include <Wire.h>
int esc = 0;
int throttle = 80;
void setup() {
Wire.begin();
Serial.begin(115200);
Serial.println("I2C Master ready!");
esc = throttle * 100 / 180;
}
void loop() {
delay(500);
Serial.println("Receive data");
Wire.requestFrom(9,32);
String response = "";
Serial.println(Wire.available());
while (Wire.available())
{
char b = Wire.read();
response += b;
}
String dataString = response;
int hashIndex = dataString.indexOf('#');
String SportData = dataString.substring(0, hashIndex);
Serial.println(SportData);
String SDdata = String (esc) + "," + String(SportData);
Serial.println(SDdata);
}
Slave Code
#include <Wire.h>
byte ANSWERSIZE= 22;
String answer = "12345,123.4,50.6,12345#";
String answerV = "4.10,4.15,4.13,4.05,4.18,0#";
void setup() {
Wire.begin(9);
Wire.onRequest(requestEvent); // data request from Master
Serial.begin(115200);
Serial.println("I2C Slave ready!");
ANSWERSIZE = answer.length();
}
void requestEvent() {
byte response[ANSWERSIZE];
for (byte i=0;i<ANSWERSIZE;i++)
{
response[i] = (byte)answer.charAt(i);
}
Wire.write(response,sizeof(response));
}
void loop() {
delay(50);
}
Can someone please show me how this can be done?

Answer 1

A simple idea is to keep track of the number of times requestEvent() is called, and use that to decide what to send back to the master.
Here is the code (n.b. I took the liberty to optimise it a bit):
Master:
#include <Wire.h>
/**
* globals
*/
int esc = 0;
int throttle = 80;
char i2c_buffer[33];
/**
* setup & loop
*/
void setup()
{
Serial.begin(115200);
Wire.begin();
esc = throttle * 100 / 180;
i2c_buffer[32] = '\0';
Serial.println("I2C Master ready!");
}
void loop()
{
delay(500);
Wire.requestFrom(9, 32);
for (byte i = 0; i < 32 && Wire.available(); ++i)
{
i2c_buffer[i] = Wire.read();
if (i2c_buffer[i] == '#') {
i2c_buffer[i] = '\0';
break;
}
}
Serial.print(esc);
Serial.print(',');
Serial.println(i2c_buffer);
}
Slave:
#include <Wire.h>
/**
* globals
*/
const byte DATA_SIZE = 2;
String data[DATA_SIZE] = {
"12345,123.4,50.6,12345#",
"4.10,4.15,4.13,4.05,4.18,0#"
};
/**
* setup & loop
*/
void setup()
{
Serial.begin(115200);
Wire.begin(9);
Wire.onRequest(requestEvent); // data request from Master
Serial.println("I2C Slave ready!");
}
void loop()
{
delay(50);
}
/**
* help functions
*/
void requestEvent()
{
static byte req_number = 0;
Wire.write(reinterpret_cast<const unsigned char*>(data[req_number].c_str()),
data[req_number].length());
req_number = (req_number + 1) % DATA_SIZE;
}
Note: I don't have two Arduino devices, so I could not test this code. If you spot some bugs, report back and I'll fix them.