![]() Input files into an output ELF and where segments belong The sections command tells the linker how to combine the ram ( rwx ) : ORIGIN = 0x20000000, LENGTH = SRAM_SIZE } Sections The stack, heap, and all variables will go.įor the SAMD21, SRAM starts at 0x20000000 and is contiguousįor the size of the SRAM. The "ram" block is mapped to the CPU's SRAM and it's where nvm ( r ) : ORIGIN = FLASH_SIZE - NVM_SIZE, LENGTH = NVM_SIZE This block is marked as read-only ( r) because flash can notīe written in the same way as normal memory, however, theĪpplication can use the SAMD's NVM peripheral to write data in Linker ensure that application code doesn't overwrite the Explicitly defining this section also lets the Regardless of how much flash space the application takes up Is useful because it means that it says in a fixed location The block is located right at the end of the flash space. User settings and calibration data in the MCU's flash. ![]() The "nvm" block is space set aside for the application to store rom ( rx ) : ORIGIN = 0x00002000, LENGTH = FLASH_SIZE - BOOTLOADER_SIZE - NVM_SIZE The total length of the rom block is the MCU's flash size minus theīootloader's size and any space reserved for "non-volatile memory"īy the application. The bootloader takes the first 0x2000 bytes of flashīootloader ( rx ) : ORIGIN = 0x00000000, LENGTH = BOOTLOADER_SIZEįollowing the bootloader is the flash memory used by the application,Ĭalled "rom" here - even though it's flash, the name is just a name The "bootloader" section allows this firmware to work with the uf2īootloader. That the linker knows that this space is read-only ( r) and The beginning of the address space ( 0x00000000) and is contiguous These blocks will be used in the SECTIONS command below. Types of data can go in the address space. Since anĪRM's address space is generally split between Flash, SRAM, peripherals,Īnd other regions, it's necessary to tell the linker where different This section declare blocks of memories for specific purposes. STACK_SIZE = DEFINED ( _stack_size_ ) ? _stack_size_ : 0x800 Memory space definition You can analyze stack usage in GCC using the -fstack-usageįlag and you can enable compiler warnings for stack usage Stack space for Cortex-M0+ projects programmed in C. The application's behavior determines just how much stack space Require stack space to be set aside in RAM. "non-volatile memory" (NVM) - which is used by the applicationįLASH_SIZE = 0x40000 /* 256kB */ BOOTLOADER_SIZE = 0x2000 /* 8kB */ NVM_SIZE = 0x400 /* 1kbB */ SRAM_SIZE = 0x8000 /* 32kB */ĪRM Cortex-M processors use a descending stack and generally This project also reserves 8kB for the bootloader and 1kB for These variables are used by the following "MEMORY" command to defineįor the SAMD21G18A used by this project, the available Flash is OUTPUT_FORMAT ( "elf32-littlearm", "elf32-littlearm", "elf32-littlearm" ) CPU memory configuration variables Section 11.1.11, Cortex M0+ Configuration The list of acceptable values can be obtained using objdump -i. Included by Atmel/Microchip out of an abundance of caution, asĪrm-none-eabi-ld will do the right thing and use "elf32-littlearm" by "elf32-littlearm" is used across the board. Since the SAM D series are configured with only little endian support, When big (-EB) or little (-EL) endian is requested. Output format sets the ELF output format to use a specific BFD backend. But if you'd like to read it here instead it's transcribed below. You can see this script in its entirety, comments and all, on GitHub. So I did a lot of research and now I can present to you the most thoroughly commented linker script 1. It's filled with incantations and mysterious symbols and there's no indication of what they're for or where they come from. So I was staring at this script that made absolutely no sense to me. elf file gets loaded by the target processor. The linker script controls how ld combines all of your. Most of us never even have to think about them, however, on memory constrained embedded devices it's not uncommon to need to modify the default linker script. If you've never heard of or seen a linker script before you're not alone. While developing the firmware for Winterbloom's Castor & Pollux, I got very curious as to just what the Microchip/Atmel-provided linker script was doing. view all posts The most thoroughly commented linker script (probably). ![]() Posted by Stargirl Flowers on January 13, 2021
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