Pic memeory code space overheads for bit varables

[longpole001]

hI CHARLES


i have a lot of code which has defined a byte with sub bit variable names



i am desperate for more code space , is there any code space advantage by not defining each bit variable , and just addressing each byte.0 directly

cheers

Sheldon

[DavidP]

Sheldon, I usually write my bit variables like this:

'******************** 'VARIABLES USED FOR CLOCK *********************
TIMEBITS VAR WORD BANK0
ROLLOVER VAR TIMEBITS.0 '1 SECOND TIMING FLAG
TX_EMPTY VAR TIMEBITS.1 'TRANSMIT BUFFER EMPTY FLAG
PARITYTYPE VAR TIMEBITS.2 'PARITY TYPE (1=ODD/0=EVEN)
RX_BUFFULL VAR TIMEBITS.3 'RECEIVER BUFFER FULL FLAG
CLEARINPT VAR TIMEBITS.4 'CLEAR INPUT BUFFER FLAG
COWSCOMHOME VAR TIMEBITS.5 'LOOP FLAG
RX_MESSAGE VAR TIMEBITS.6 'MESSAGE AVAILABLE FLAG
PATDOG VAR TIMEBITS.7 'WATCHDOG FLAG (BONE)
ONETICK VAR TIMEBITS.8 '10 MILLISECOND A/D PACING FLAG
TENTICK VAR TIMEBITS.9 '100 MILLISECOND PACING FLAG
SECTICK VAR TIMEBITS.10 '1 SECOND PACING FLAG
LZB VAR TIMEBITS.11 'LEAST SIGNIFICANT BIT FLAG
DISPFLAG VAR TIMEBITS.12 '1 SECOND ANALOG DISPLAY UPDATE FLAG
PASSENABLE VAR TIMEBITS.13 'PASSWORD ENABLE FLAG
QUE VAR TIMEBITS.14
FIVETENTICK VAR TIMEBITS.15

[Charles Leo]

You're asking about Code Space, correct? Not RAM where the variables reside.

The biggest effect that variables have on code space relates to the bank where they are located. If PBP doesn't have to change banks to access a variable, it saves one location of code space for the operation. I've worked on some code in the past where I experimented with BANK modifiers when declaring variables in order to reduce code space usage. The results were there, but I don't know if I would call them significant. This happened before the code space was increased on newer PICs, so the concern has diminished.

I would guess there are other techniques that would yield much more savings than variable manipulation.

In answer to your specific question about a bit-alias vs a byte.bit name, they are the same. Aliases in PBP are just text substitutions. They don't affect the compiled code.

[longpole001]

ok thanks , yes i thought there be little to be gained in just changing this item ,