Waiting for character in string - c

Question

I am currently working on a project that will be used to test whether an instrument is within tolerance or not. My test equipment will put the DUT (Device Under Test) into a "Test Mode" where it will repeatedly send a string of data every 200ms. I want to receive that data, check is is within tolerance and give it a pass or fail.
My code so far (I've edited a few things out like .h files and some work related bits!):
void GetData();
void CheckData();
char Data[100];
int deviceId;
float a;
float b;
float c;
void ParseString(const char* stringValue)
{
char* token = NULL;
int tokenPlace = 0;
token = strtok((char *) stringValue, ",");
while (token != NULL) {
switch (tokenPlace) {
case 0:
deviceId = atoi(token);
break;
case 1:
a= ((float)atoi(token)) / 10.0f;
break;
case 2:
b= ((float)atoi(token)) / 100.0f;
break;
case 3:
c= ((float)atoi(token)) / 10.0f;
break;
}
tokenPlace++;
token = strtok(NULL, ",");
}
}
void GetData()
{
int x = UART.scanf("%s,",Data);
ParseString(Data);
if (x !=0) {
UART.printf("Device ID = %i\n\r", deviceId);
UART.printf("a= %.1f\n\r", a);
UART.printf("s= %.2f\n\r", b);
UART.printf("c= %.1f\n\n\r", c);
}
if (deviceId <= 2) {
CheckData();
} else {
pc.printf("Device ID not recognised\n\n\r");
}
}
void CheckData()
{
if (a >= 49.9f && a< = 50.1f) {
pc.printf("a Pass\n\r");
} else {
pc.printf("a Fail\n\r");
}
if (b >= 2.08f && b <= 2.12f) {
pc.printf("b Pass\n\r");
} else {
pc.printf("b Fail\n\r");
}
if (c >= 20.0f && c <= 25.0f) {
pc.printf("c Pass\n\n\r");
} else {
pc.printf("c Fail\n\n\r");
}
if (deviceId == 0) {
(routine1);
} else if (deviceId == 1) {
(routine2);
} else if (deviceId == 2) {
(Routine3);
}
}
int main()
{
while(1) {
if(START == 0) {
wait(0.1);
GetData();
}
}
}
And this works absolutely fine. I am only printing the results to a serial terminal so I can check the data is correct to make sure it is passing and failing correctly.
My issue is every now and then the START button happens to be pressed during the time the string is sent and the data can be corrupt, so the deviceId fails and it will say not recognised. This means I then have to press the start button again and have another go. A the moment, it's a rare occurrence but I'd like to get rid of it if possible. I have tried adding a special character at the beginning of the string but this again gets missed sometimes.
Ideally, when the start button is pressed, I would like it to wait for this special character so it knows it is at the beginning of the string, then the data would be read correctly, but I am unsure how to go about it.
I have been unsuccessful in my attempts so far but I have a feeling I am overthinking it and there is a nice easy way to do it. Probably been staring at it too long now!
My microcontroller is STM32F103RB and I am using the STM Nucleo with the mBed IDE as it's easy and convenient to test the code while I work on it.

Answer 1

You can use ParseString to return a status indicating whether a complete string is read or not.
int ParseString(const char* stringValue)
{
/* ... your original code ... */
/* String is complete if 4 tokens are read */
return (tokenPlace == 4);
}
Then in GetData use the ParseString return value to determine whether to skip the string or not.
void GetData()
{
int x = UART.scanf("%s,",Data);
int result = ParseString(Data);
if (!result) {
/* Did not get complete string - just skip processing */
return;
}
/* ... the rest of your original code ... */
}