C51/LX51: Place some variables in a specific page apart

 C51/LX51: Place some variables in a specific page apart

Hello,

I am working on a project based on a C8051F353 from Silabs.
This project needs some non-volatile variables to be stored, using internal Flash.
I manage to read, write, and erase data to flash BUT:
-a write needs an erase, and erase can't be performed on less than a page
All data can be kept, by reading the concerned page, modify the requested data, erasing the page, and write the modified copy.

Since I have declared my non-volatile data into the main program as global variables with "code" prefix, this data is located into program in Flash. When I want to write to this data, I am so erasing and rewriting page of running program, which results in reset of device.

I would like to be able to place non-volatile data into a specific page appart from code, into flash. So that I won't affect program when updating data.
I think the use of SEGMENTS would be the best for me, but I can't manage to place a specific segment in a specific page, but just at the end of code.

I somebody have a solution, or can give me a direction to fix this problem.

Thank you in advance.

 have you read the datasheet ...

... re the scratchpad?

Erik

 RE: have you read the datasheet ...

Thank you for the answer,

Yes I read Device, C51, and LX51 datasheets but didn't find what I expect to do.
The only time I find something related to scratch pad is in 11.2 Data memory part of the 8051F353 datasheet, which deal of RAM. I can't see how this feature is related to my wishes to store variables to Flash.

If there is a use of this scratch pad in my case, please explain me briefly how.

Thank you,
Simon.

 sorry

did not know that SILabs had chips with no scratchpad

Erik

 what I would do ...

... would be to make a small assembler routine that defines the location and does erase and write (read is in C). This also avoids the chance that the C code decides to write some variable other than the "configurations data" to memory, which when directed to flash would be disastrous.

In assembler you have it "by the balls" and can locate to your hearts delight. Declare the "flash storege start" in the assembler fil and meke it public.

Erik

 RE: what I would do ...

No problem.

I was thinking about a dynamic way to allocate a page, in relation to the compiled code.
Isn't it possible with SEGMENTS? The PAGE Alignment Type would be perfect for that (cf http://www.keil.com/support/man/docs/lx51/lx51_in_cmb_segments.htm) but I can't find a way to set this setting by myself instead the linker.

The LX51 documentation for Raisonance explain how to perform an Alignment relocation, and I was expected it was possible with the Keil version.
If there is no solution with that, I will place manually my variables at specific adresses, out of code (but I am not able to know before compiling the adresses used for porgram).

Am I right?

 you do not want to do that because

I was thinking about a dynamic way to allocate a page, in relation to the compiled code.
you do not want to do that because that may lead to losing the config data when upgrading the code, put it in the lsat page.

The LX51 documentation for Raisonance explain how to perform an Alignment relocation, and I was expected it was possible with the Keil version.
it is, but I am, for the '51 "IDE dumb" because I have done all my '51 stuff by commandlime

Erik

 RE: you do not want to do that because

you do not want to do that because that may lead to losing the config data when upgrading the code
It is not a problem for me since the device should be programmed just one time, and we have parameters in a database. The non-volatile parameters are modified by code via UART communication, and without updating the code.

Placing them to the last page (I think about using absolute location using ^0x1dFF as adress to specify the last adress of the last page) seems to be the best idea.

How am I sure that the code won't overwrite this dataspace? Will the linker inform me about that?

Thank you Erik.

 famous last words

the device should be programmed just one time
famous last words

Placing them to the last page (I think about using absolute location using ^0x1dFF as adress to specify the last adress of the last page) seems to be the best idea.
beware of the special bits in the last page, refer to the flash map in the datasheet. Look up page size vs. start of config area.

How am I sure that the code won't overwrite this dataspace? Will the linker inform me about that?
the linker has a parameter "size of CODE memory" again, I do not know how to initialize it in the IDE. This, will keep the code out of the last bit of memory.

Erik

 RE: famous last words

beware of the special bits in the last page
You're right. I noticed few time after my post that my flash was write protected. The last byte of the last page is a security byte and any erase request on this page generates a reset. So I mustn't use the last page for my non volatile variables.

I'm going to look for the size of code parameters.

Thnak you.