topic Re: Why .bss section is placed in Flash? in LPC Microcontrollers

Why .bss section is placed in Flash?

jtro — Mon, 02 Sep 2019 10:14:22 GMT

I observed that when I'm increase or decrease variable array size, flash size is also change.

I have seen in Flash Memory contents it shows .bss section which occupy considerable amount of Flash why .bss section comes in Flash?? It should be there in RAM section only.

I have even check linker setting in project setting but no option available?

I wonder why .bss section is mapped in SRAM and how to change it?

Re: Why .bss section is placed in Flash?

BlackNight — Mon, 02 Sep 2019 16:52:34 GMT

Maybe you could share some details about what you see?

Maybe you see the problem described here: GNU Linker, can you NOT Initialize my Variable? | MCU on Eclipse

I hope this helps,

Erich

Re: Why .bss section is placed in Flash?

jtro — Tue, 03 Sep 2019 06:01:07 GMT

No this is not like that.. I know basic concept of .data, .bss,..etc. If any data is initialized with any value then it considered as .data not .bss.

In my case

1) suppose array size is 256

uint8_t variable[256];

I got below memory usage in MXUXpresso

In Image Info -> Memory Usage

Program Flash - 13.47 KB

SRAM - 4.52 KB

In console window after compilation

text data bss dec hex filename
9311 64 4560 13935 366f test.axf

2) Changed array size to 1024

uint8_t variable[1024];

I got below memory usage in MXUXpresso

In Image Info -> Memory Usage

Program Flash - 14.23 KB (increased by 768)

SRAM - 5.27 KB

In console window after compilation

text data bss dec hex filename
9315 64 5328 14707 3973 test.axf

After compare above result i thought there may have some error in memory usage calculation in Image Info or something I'm missing not sure..

Result in console window is ok.

Why image Info show wrong memory usage??

Re: Why .bss section is placed in Flash?

BlackNight — Tue, 03 Sep 2019 08:48:51 GMT

I tried the same, but I have to say it is correct for me (using a K22 device):

With this

uint8_t var[256];

I get

Region   Start address       End address       Free   Used   Usage (%)
PROGRAM_FLASH   0x0       0x40000       262144   254436   7708   2.94%
SRAM_UPPER   0x20000000   0x20004000   16384   13880   2504   15.28%
SRAM_LOWER   0x1fffc000   0x20000000   16384   16384   0   0.00%
FLEX_RAM   0x14000000   0x14001000   4096   4096   0   0.00%

and with this

uint8_t var[256+1024];

I get

Region       Start address   End address       Free   Used   Usage (%)
PROGRAM_FLASH   0x0       0x40000       262144   254436   7708   2.94%
SRAM_UPPER   0x20000000   0x20004000   16384   12856   3528   21.53%
SRAM_LOWER   0x1fffc000   0x20000000   16384   16384   0   0.00%
FLEX_RAM   0x14000000   0x14001000   4096   4096   0   0.00%

which is what I expect.

Can you share your project here so the engineers could have a look?

Re: Why .bss section is placed in Flash?

jtro — Tue, 03 Sep 2019 09:55:42 GMT

Please check workspace..

Go to UART.h file and change buffer value.

Re: Why .bss section is placed in Flash?

FelipeGarcia — Wed, 04 Sep 2019 15:27:29 GMT

Hello,

I checked your project and did the following:

Build the project and got the following results

Memory region         Used Size Region Size %age Used
   PROGRAM_FLASH:        4612 B      24560 B     18.78%
    PRODUCT_INFO:          0 GB         16 B      0.00%
            SRAM:        4288 B        16 KB     26.17%
Finished building target: bss.axf

make --no-print-directory post-build
Performing post-build steps
arm-none-eabi-size "bss.axf" ; arm-none-eabi-objcopy -v -O binary "bss.axf" "bss.bin" ; # checksum -p LPC845 -d "bss.bin"
   text           data            bss            dec            hex        filename
   4608              4           4284           8896           22c0        bss.axf

Then, I increased txBuffer as you suggested:

And I got the results below:

Memory region         Used Size Region Size %age Used
   PROGRAM_FLASH:        4612 B      24560 B     18.78%
    PRODUCT_INFO:          0 GB         16 B      0.00%
            SRAM:        5312 B        16 KB     32.42%
Finished building target: bss.axf

make --no-print-directory post-build
Performing post-build steps
arm-none-eabi-size "bss.axf" ; arm-none-eabi-objcopy -v -O binary "bss.axf" "bss.bin" ; # checksum -p LPC845 -d "bss.bin"
   text           data            bss            dec            hex        filename
   4608              4           5308           9920           26c0        bss.axf

It seems the bss is increased correctly, could you please clarify if you are doing something differently or if I missed something?

Best regards,

Felipe

Re: Why .bss section is placed in Flash?

1234567890 — Wed, 04 Sep 2019 20:35:06 GMT

Well, if you increase the array from 256 to 1024 the difference is 768. I can't see a fault neither in Image Info nor in console. Image Info has a very small difference because of the unit in kB (not really, but it looks like).

Obviously I don't understand the problem; please describe again more clearly.

Re: Why .bss section is placed in Flash?

jtro — Thu, 05 Sep 2019 03:57:01 GMT

As i told in earlier post, Console shows correct value but Image Info shows wrong value. Please compare below images with different buffer size.

With 256:

with 4096:

Hope above image is enough to describe my issue.

Re: Why .bss section is placed in Flash?

converse — Thu, 05 Sep 2019 19:39:35 GMT

May be worth trying v11.0.1. The release notes include the comment:

Fixed various issues with Image Info view

Re: Why .bss section is placed in Flash?

jtro — Fri, 06 Sep 2019 04:12:32 GMT

Tried with latest software v11.0.1. No difference.

Getting same result.

Re: Why .bss section is placed in Flash?

converse — Fri, 06 Sep 2019 08:08:17 GMT

I just had a quick look, using the 'bss' project that you provided previously.

First comment is that the figures provide in the Memory Usage tab are those that are output by the linker when using --print-memory-usage, so it is the linker that is generating her numbers.

So, using the

U8 au8RxBuffer[4096];

I see

PROGRAM_FLASH: 4612 B 24560 B 18.78%

PRODUCT_INFO: 0 GB 16 B 0.00%

SRAM: 4288 B 16 KB 26.17%

and when using

U8 au8RxBuffer[256];

I see

PROGRAM_FLASH: 4620 B 24560 B 18.81%

PRODUCT_INFO: 0 GB 16 B 0.00%

SRAM: 448 B 16 KB 2.73%

So the only significant difference is that SRAM increases by 3840 bytes (the difference being the increase in the buffer size (4096-256).

This is using the application that you posted, with the only change being the size of auRxBuffer. What is it that you are doing that is different?

[EDIT]

Comparing the numbers shown in the Image Info view - I DO see your problem. This looks like a bug in the ImageInfo viewer @NXP - can somebody look into this?

Re: Why .bss section is placed in Flash?

jtro — Fri, 06 Sep 2019 08:17:51 GMT

As I said in earlier post In console tab everything is OK only issue is in Image Info tab.

compare Usage (%) in previous post where i have shown you with memory usage with different buffer size.

Region PROGRAM_FLASH should not change if i change buffer value.

Re: Why .bss section is placed in Flash?

jtro — Mon, 09 Sep 2019 09:00:24 GMT

Any update on this??

Re: Why .bss section is placed in Flash?

jtro — Wed, 18 Sep 2019 04:05:40 GMT

No reply from NXP..!!

When problem is resolved?

I'm waiting for solution.

Re: Why .bss section is placed in Flash?

FelipeGarcia — Wed, 18 Sep 2019 19:29:39 GMT

Hi,

It seems that the image info data is incorrect. I recommend you to see the console instead we will fix this in the next release.

Best regards,

Felipe