topic Re: BSS fill with data_alignment in Kinetis Design Studio

BSS fill with data_alignment

leccy — Tue, 12 Jul 2016 08:56:34 GMT

I have recently ported USB MSD boot-loader AN4379 from CW 10.4 to KDS.

With some adaptations, we have been running the boot-loader on several products for a couple of years.

On KDS, however, I cannot get the project to compile without a linker error. It shows an over-spill of 840 bytes in RAM.

Looking at the .map file, I see there is a *fill* section in BSS of 0x1e4 bytes (484):

.bss 0x1fff0400 0x1b40 load address 0x00008600

0x1fff0400 __START_BSS = .

0x1fff0400 PROVIDE (__bss_start__, __START_BSS)

*(.bss)

.bss 0x1fff0400 0x1c c:/freescale/kds_3.0.0/toolchain/bin/../lib/gcc/arm-none-eabi/5.4.1/armv7e-m/crtbegin.o

*(.bss*)

*fill* 0x1fff041c 0x1e4

.bss.g_Mem 0x1fff0600 0x400 ./Sources/USB/driver/usb_dci_kinetis.o

.bss.g_bdtmap 0x1fff0a00 0x4 ./Sources/USB/driver/usb_dci_kinetis.o

0x1fff0a00 g_bdtmap

The global g_Mem must be aligned to a 512 byte boundary since it is filled by the DMA:

#if defined(__GNUC__)

__attribute__((__aligned__(512)))

#elif defined(__IAR_SYSTEMS_ICC__)

#pragma data_alignment = 512

#endif

static uint_8 g_Mem[BYTES_1024];

Any ideas why the linker does not place any other variables in the BSS region up to g_Mem?

The CW10.4 compilation does this.

Re: BSS fill with data_alignment

BlackNight — Tue, 12 Jul 2016 11:35:37 GMT

Hi Alex,

I don't think the GNU linker in CodeWarrior handles this differently. The GNU linker is going through the linker script file in a linear way, and does not try to fill up things or distribute variables into different memory areas (I whish the GNU ld could do this, this is a long time wish from many users).

Anyway, the thing is that you should allocate the USB buffer at the beginning of a section (which is already aligned to the 512 byte boundary. That way the linker has not to add *fill* bytes. See https://mcuoneclipse.com/2014/07/11/switching-arm-gnu-tool-chain-and-libraries-in-kinetis-design-studio/comment-page-1/#…

I hope this helps,

Erich

Re: BSS fill with data_alignment

leccy — Tue, 12 Jul 2016 14:00:45 GMT

Thanks Erich

Already done that from my same question on yr blog.

BTW, I was using the CW tool-chain on the CW project, not the GNU.

Re: BSS fill with data_alignment

BlackNight — Tue, 12 Jul 2016 15:30:00 GMT

Hi Alex,

ok, then it makes sense: the non-GNU ARM toolchain used a custom linker implementation, and that linker was able to fill gaps in the memory map.

Erich