I'm looking at ways to minimize my ram usage and increase performance.
Based on your past experience - please comment on an opinion I have. I'm looking for confirmation or - "Your Head is up your Ass on that one" reply.
I'm using an RTOS, so each task associated with the RTOS has a while loop - so you never exit from the function (standard RTOS implementation). Local stack variables are always consumed and never reused.
I'm using Kinetis ARM micros - so they are all 32 bit cpus.
Local variables used within the RTOS task function always utilize the space of a 32 bit word (I'll call it a DWORD), whether ii's a BYTE (8 bits), or a WORD (16 bits).
So a local BYTE consumes 4 bytes from the stack. The compiler also has to add additional code to make sure the outcome of operations stay within the BYTE range.
SO .. local BYTEs and WORDs - consume more space than required and adds a small performance hit due to the additional processing required to make sure the operations are within range.
My opinion -- NOW ....
To save memory (actually stack space which could then be reduced) - move local BYTE and WORD variable out into global space.
When a BYTE is declare global -- you only consume 1 byte of memory instead of 4 on the stack and the additional range operations are not required.
I looked at a task where I had 6 byte variables defined - that's 24 bytes of stack consumed. By making them global -- I only consume 6.
Your thoughts based on your experience.