Hi, I'm pretty new to understanding the low-level working of ARM uC. Right now I have a project that require fairly large amount of heap (~24K). The default LPC1768 linkerscript put the heap in the leftover space from 32K RAM, which for my case won't be enough.
I have an idea to move the .data and .bss sections to the unused 16K RAMs and use the whole 32K RAM as heap (minus the ISR vectors and IAP of course). This should work, right?
I've successfully move the .data section to USB_RAM. But when I move the .bss to USB_RAM, the code isn't working properly. Looks like as if the memory isn't even allocated.
Putting .data > USB_RAM, .bss > USB_RAM, .heap > RAM does not work:
.data : AT(__etext)
{
__data_start__ = .;
/* data stuff */
__data_end__ = .;
} > USB_RAM
.bss :
{
__bss_start__ = .;
*(.bss*)
*(COMMON)
__bss_end__ = .;
} > USB_RAM
.heap (NOLOAD):
{
__end__ = .;
*(.heap*)
. = ORIGIN(RAM) + LENGTH(RAM);
__HeapLimit = .;
} > RAM
But putting .data > USB_RAM, .bss > RAM, .heap > RAM works, or any other combinations that doesn't involve putting .bss > USB_RAM really.
Even looking at the map file when .bss > USB_RAM, I don't really see why the code doesn't work. The .bss is there where it expected to be:
...
0x000000002007d984 PROVIDE (__init_array_end = .)
0x000000002007d988 . = ALIGN (0x8)
*fill* 0x000000002007d984 0x4
[!provide] PROVIDE (__fini_array_start = .)
*(SORT_BY_NAME(.fini_array.*))
*(.fini_array)
.fini_array 0x000000002007d988 0x4 /opt/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v7-m/nofp/crtbegin.o
[!provide] PROVIDE (__fini_array_end = .)
0x000000002007d990 . = ALIGN (0x8)
*fill* 0x000000002007d98c 0x4
0x000000002007d990 __data_end__ = .
.igot.plt 0x000000002007d990 0x0 load address 0x00000000000109e4
.igot.plt 0x000000002007d990 0x0 /opt/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v7-m/nofp/crtbegin.o
.bss 0x000000002007d990 0x1028 load address 0x00000000000109e8
0x000000002007d990 __bss_start__ = .
*(.bss*)
.bss 0x000000002007d990 0x1c /opt/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v7-m/nofp/crtbegin.o
.bss.d1 0x000000002007d9ac 0x8 BUILD/gw/gateway/main.o
0x000000002007d9ac d1
.bss.d2 0x000000002007d9b4 0x8 BUILD/gw/gateway/main.o
0x000000002007d9b4 d2
.bss.pBus 0x000000002007d9bc 0x4 BUILD/gw/gateway/main.o
...
I'm using mbed 5.14 by the way.
