Question

I have 8 bit samples with random values (called headers) and I have commands with hexadecimal values, see bellow:

[8 bit][command]
 \      |
  \     \------------------ [01 30 00 00 = hex start the machine]
   \
   +-------------------+
   | 00001111 = hi     |
   | 00000000 = hello  |
   | 00000101 = wassup |
   +-------------------+

How do you translate the 8 bit samples to 1 byte and join it with the above hex value ?

Answer 1

In both languages, you can use bitwise operations.

So in C, if you have:

uint32_t command;
uint8_t  sample;

You can concatenate these into e.g. a 64-bit data type as follows:

uint64_t output = (uint64_t)command << 32
                | (uint64_t)sample;

If you instead want an array of output bytes (for serializing over RS-232 or whatever), then you can do something like:

uint8_t output[5];
output[0] = sample;
output[1] = (uint8_t)(command >>  0);
output[2] = (uint8_t)(command >>  8);
output[3] = (uint8_t)(command >> 16);
output[4] = (uint8_t)(command >> 32);