CC2541: How to configure Negative values in SimpleBLEPeripheral example code

Hi Vishnu,

Sorry I'm not able to give you sample code that does what you want in the project you want.

Are you aware of how memory works in C? Basically whatever variable you have, what type it is and what size it is, it is addressable as an array of bytes.

Let's say there's a function that expects a "buffer", which in the API is normalized to uint8_t* or sometimes void*;
void MyBufferEatingFunction(uint8_t *buf, uint16_t bufLen);

Now it happens that what you have is an array of signed integers;
int32_t myNegativeNumbers[5] = { -1, -2, -400, -33, -50 };

You use this array as you normally use an array of this type. Everything is nice and everyone is happy.

Now, someone has given you a transmit function that requires an array of consecutive bytes like above. Luckily that is just another way of looking at the array of negative numbers because everything after all is just byte-addressable memory.

If you want to be explicit, you then declare a pointer that has this way of looking at your array;
uint8_t *myCharBuf = (uint8_t *)myNegativeNumbers;

These two (myCharBuf and myNegativeNumbers) now point to the same memory, but "looks" at it differently.

Let's call the function;
MyBufferEatingFunction(myCharBuf, sizeof(myNegativeNumbers));

Notice that this gives no warnings because we explicitly cast the memory that we give to the function. The following would produce a warning;
MyBufferEatingFunction(myNegativeNumbers, sizeof(myNegativeNumbers));

Because you have in fact given it an unexpected type (int32_t[] instead of uint8_t*). It would work however, but the type-checking gives a warning. However since you know what you are doing, you cast the memory explicitly to tell the compiler that you do in fact know what you are doing.

In your case, the stack APIs are expecting uint8_t pointers, but you are giving it something else.

I would direct your attention to SimpleLink Academy, and the tutorial on custom profiles. The functionality is very similar to CC2541 although the guide is for CC2640R2. dev.ti.com/.../

If you have other questions about C programming I would suggest a forum targeting programming questions.

Best regards,
Aslak