Data memory is a problem

F

fourtytwo

Active Member

• Jan 3, 2023

• #2

What toolchain is that ?
Some sort of C ?
I use MPASM and UDATA_ACS works perfectly.

 

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Peet19

Member

• Jan 4, 2023

• #3

I do not understand what you mean. in Assembly
(CBLOCK) with
I reserved 100 registers from the memory for the sake of the example.
Everything is fine with this, because I can see in the file registers window that it is indeed reserved and can be used, but I don't get feedback about the data memory usage. Why is this?
I cannot use UDAT_ACS because I use an 18F24K22 microcontroller. As far as I know, UDATA_ACS can only be used with PIC18Cxxx controllers.

 

Last edited: Jan 4, 2023

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Peet19

Member

• Jan 4, 2023

• #4

Look. I reserve 2 registers named CNT1 and CNT2 at addresses 0x008 and 0x009 using CBLOCK. So two 8-bit registers are reserved, i.e. 2 bytes of reserved data memory. But there is no feedback about data memory usage. I do not understand this.

 

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Nigel Goodwin

Super Moderator

Most Helpful Member

• Jan 4, 2023

• #5

Are those registers referenced in the program?, and have you assembled the program?.

 

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Ian Rogers

User Extraordinaire

Forum Supporter

Most Helpful Member

• Jan 4, 2023

• #6

Nigel Goodwin said:

Are those registers referenced in the program?, and have you assembled the program?.

Click to expand...

Just what I was gonna say..

 

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W

Wp100

Well-Known Member

• Jan 4, 2023

• #7

Just run up an old program, pic18F45K22 in mplab8.92 and that does use the registers specified and also get nothing showing in the Gauge.
Looking on the web, seems its a common problem but not seen any actual answer ?

 

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rjenkinsgb

Well-Known Member

Most Helpful Member

• Jan 4, 2023

• #8

In the present version of MPLab X, memory use is only shown after compiling the program.

Also, if the program is not being built in "debug" mode, it relies on the option

"Load symbols when programming or building for production"

being ticked in the project properties -> Loading section.
(I don't know if anything of that applies to MPLab 8, I've not used that in many years)

 

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T

tumbleweed

Well-Known Member

Most Helpful Member

• Jan 4, 2023

• #9

CBLOCK does not allocate ram... what CBLOCK does is assign constant values to the symbols declared inside it. It's basically the same as a sequence of EQUs.

The way to actually allocate ram is to use RES, and that's only available in relocatable mode.
I think you'll only see the 'Data Memory' in the usage gauge is if you use one of the UDATA directives and RES

 

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Peet19

Member

• Jan 5, 2023

• #10

You are right, thank you. I just don't understand why it doesn't allow addresses below 0x060 to be reserved. Maybe that's why ACCESS RAM uses it?

DA1: UDATA 0x060
DAT1 RES 1
DAT2 RES 1
DAT3 RES 2
DAT4 RES 1

that's how it worked

 

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T

tumbleweed

Well-Known Member

Most Helpful Member

• Jan 5, 2023

• #11

for PIC18 devices locations in the access ram are declared using UDATA_ACS.

I just double-checked, and what I said before about RES isn't correct... according to the mpasm users guide you can use RES with both absolute and relocatable code.

 

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Peet19

Member

• Jan 5, 2023

• #12

I did it, thanks.
So which one should I use now? CBLOCK or UDATA_ACS?
I don't understand the difference. Can you help me?

DATAS: UDATA_ACS 0x010
DAT1 RES 1
DAT2 RES 1
DAT3 RES 1
DAT4 RES 1

 

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T

tumbleweed

Well-Known Member

Most Helpful Member

• Jan 5, 2023

• #13

If you don't care about that data memory usage gauge and you're using absolute mode then you can use CBLOCK and manage everything yourself like before.

 

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Peet19

Member

• Jan 5, 2023

• #14

OK thank you. The absolute mode is more sympathetic because then I can see my reserved registers in the watch window.

 

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Peet19

Member

• Jan 6, 2023

• #15

I have one more quick question. What do absolute and relocatable codes mean?

 

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rjenkinsgb

Well-Known Member

Most Helpful Member

• Jan 6, 2023

• #16

In general terms:
Absolute means data memory and program addresses are given explicitly in the program.

Relocatable means addresses are given as relative offsets to the program counter or another register, so the program does not need to be loaded to any specific address in the CPU memory space, it can run equally well at any location.

There are variations & different IDEs or compilers may use different terminology; ie. if you are building a program that uses multiple separate source files, they may all apparently use the same addressing, but the compiler "loader" program patches all the additional file addresses as it builds the complete machine code program & sequences them after the main module, to give each part a different address range.

Plus things such as Windows .exe files, which are absolute but include a patch table the operating system uses to adjust all the values in absolute address instructions, so the program can run from any location once the OS has finished patching it.

 

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Peet19

Member

• Jan 7, 2023

• #17

I understand, thank you. If I understand correctly, the relocatable is a better solution?
Why don't my own registers appear in relocatable mode in the Watch window?

 

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T

tumbleweed

Well-Known Member

Most Helpful Member

• Jan 7, 2023

• #18

In relocatable mode you have to use the linker (MPLINK) to generate a .cof file with symbolic info.
There should be a copy of the "MPASM_MPLINK_User_Guide.pdf" in your mpasm install folder.

 

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