Much ROM memory used when declaring RAM

[Ivar Boer]

Dear all,

Iam using an PIC16F877 for a fan controller project with a 16 bits RAM pointer.
At this moment my ROM usage is 89\%.

When iam declaring 3 bytes (3 * int8) my ROM usage is increased from 89\% to 92\%.

Can someone tell why this is happening and how i can resolve this problem?
(I need a quick answer to be in time for my finishing date)

Thanks!

Ivar
___________________________
This message was ported from CCS's old forum
Original Post ID: 10493

[Tomi]

<font face="Courier New" size=-1>Try to declare your new variables as close as possible to the other variables used in the same functions. Place your frequently used variables onto the first page.
Handling variables involves page handling and if you are not really lucky then you can write a program where the every second lines contain page swapping. Here is a piece of code for example (check your code for page bit handling):
0000 00630 .................... for (bytecnt=0;bytecnt<4;bytecnt++) {
014E 1703 00631 BSF 03,6
014F 01AA 00632 CLRF 2A
0150 1303 00633 BCF 03,6
0151 3004 00634 MOVLW 04
0152 1703 00635 BSF 03,6
0153 022A 00636 SUBWF 2A,W
0154 1C03 00637 BTFSS 03,0
0155 2958 00638 GOTO 158
0156 1303 00639 BCF 03,6
0157 2BA8 00640 GOTO 3A8
0158 1303 00641 BCF 03,6
0000 00642 .................... if (buff & bits[bytecnt]) {
0159 1703 00643 BSF 03,6
015A 082A 00644 MOVF 2A,W
015B 1303 00645 BCF 03,6
___________________________
This message was ported from CCS's old forum
Original Post ID: 10498

[Ivar Boer]

Thank you very much for your answer.

I think this could help a bit for general programming, but the problem is that a lot of ROM is used without using the RAM members in my code, so this is not the reason.


:=<font face="Courier New" size=-1>Try to declare your new variables as close as possible to the other variables used in the same functions. Place your frequently used variables onto the first page.
:=Handling variables involves page handling and if you are not really lucky then you can write a program where the every second lines contain page swapping. Here is a piece of code for example (check your code for page bit handling):
:=0000 00630 .................... for (bytecnt=0;bytecnt<4;bytecnt++) {
:=014E 1703 00631 BSF 03,6
:=014F 01AA 00632 CLRF 2A
:=0150 1303 00633 BCF 03,6
:=0151 3004 00634 MOVLW 04
:=0152 1703 00635 BSF 03,6
:=0153 022A 00636 SUBWF 2A,W
:=0154 1C03 00637 BTFSS 03,0
:=0155 2958 00638 GOTO 158
:=0156 1303 00639 BCF 03,6
:=0157 2BA8 00640 GOTO 3A8
:=0158 1303 00641 BCF 03,6
:=0000 00642 .................... if (buff & bits[bytecnt]) {
:=0159 1703 00643 BSF 03,6
:=015A 082A 00644 MOVF 2A,W
:=015B 1303 00645 BCF 03,6
:= ___________________________
This message was ported from CCS's old forum
Original Post ID: 10502

[R.J.Hamlett]

:=Dear all,
:=
:=Iam using an PIC16F877 for a fan controller project with a 16 bits RAM pointer.
:=At this moment my ROM usage is 89\%.
:=
:=When iam declaring 3 bytes (3 * int8) my ROM usage is increased from 89\% to 92\%.
:=
:=Can someone tell why this is happening and how i can resolve this problem?
:=(I need a quick answer to be in time for my finishing date)
:=
:=Thanks!
:=
:=Ivar
Firstly, if you are using '#zero_ram', in the code, then adding new variables, will correspond to other addresses to be cleared. Secondly, if you declare a variable with a statement like:
int fred=8;
Then the code to initialise the variable will be added.
A simple declaration like:
int fred;
will normally add nothing to the code involved, _but_ if the system has to move another variable into a different memory bank to make way for this, then extra bank switching code will be added, even if the new variable is not used. It is allways worth declaring commonly used variables together, since this tends to result in these being placed together in RAM.

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 10505