Using ITIM in assembly

HiFive1 Rev B
1

Hi,

I’m somewhat new this whole embedded game so apologies in advance if I’ve made some obvious mistakes here.

I’ve been playing around running in pure assembly on my hifive1 rev B and was trying to test running code from the ITIM. I’ve read the FE310-G002 manual and also tried to look at what the example-itim project does in the freedom-e-sdk, but I don’t think I’ve got it quite right.

I was hoping it would be a case of sticking a “.section .itim” in my file but there’s probably more I’m missing.

Here is my main assembly file:

.section .text

.global _start
_start:
    .cfi_startproc
    .cfi_undefined ra

    # Global Pointer setup
    .option push
    .option norelax
    la gp, __global_pointer$
    .option pop

    # Stack Pointer setup
    la sp, __stack_pointer$

    j _testie

    .cfi_endproc

My other test file:

.section .itim

.global _testie
_testie:
    addi t0, t0, 1
    j _testie

my linker script:

OUTPUT_ARCH("riscv")

ENTRY(_start)

MEMORY
{
    itim : ORIGIN = 0x8000000,  LENGTH = 8K
    ram  : ORIGIN = 0x80000000, LENGTH = 16K
    rom  : ORIGIN = 0x20010000, LENGTH = 512M
}

SECTIONS
{
    __stack_size = DEFINED(__stack_size) ? __stack_size : 2K;

    .text : {
        *(.text*)
    } > rom

    .rodata : {
        *(.rodata*)
    } > rom

   .itim : ALIGN(8) {
        *(.itim*)
    } > rom

    .data : ALIGN(8) {
        *(.data*)
        . = ALIGN(8);
        PROVIDE( __global_pointer$ = . + 0x800 );
    } > ram AT > rom

    .bss (NOLOAD): ALIGN(8) {
        *(.bss*)
        *(COMMON)
    } > ram

    .stack ORIGIN(ram) + LENGTH(ram) - __stack_size : ALIGN(16) {
        PROVIDE( __stack_pointer$ = . );
    } > ram

}

and these are the options I’m passing to the assembler/linker:

ARCH=rv32imac
ABI=ilp32
EMU=elf32lriscv

ARCHFLAGS=-march=rv32imac -mabi=ilp32
CFLAGS=$(ARCHFLAGS) -g -o0
LDFLAGS=-m $(EMU) -nostartfiles -nostdlib -Tlnk.lds
AS=riscv64-unknown-elf-as
LD=riscv64-unknown-elf-ld

Not sure if there’s anything else I can provide that will be of use

2

Not sure what’s the problem that you are facing here. I assume you tried to compile and link the code to ITIM section and such code can’t be found there.

If that’s the case, couple suggestions. 1st, freedom-e-sdk BSP for hifive1 board has the ITIM defined in the linker script. You can use it 1st then debug the problem later. See freedom-e-sdk-root/bsp/sifive-hifive1-revb/metal.default.lds for detail.

To do quick test, you can use function attribute to link a C function to ITIM section in C code.

 __attribute__((section(".itim"))) void myfunc() {
volatile int i=0;
i++;
return;
}

Once you have a working linker script then you can check your assembly code. I did not spot any obvious problem here.

2nd thing to check is whether the function that is linked to the ITIM are called in the main program. By default freedom-e-sdk will remove unused function.

3rd thing to check is use -fno-inline force compile don’t inline the code.

This is not related to your problem but notice that we have “-o0” in the CFLAGS. It should be “-O0”.

3

Thanks for the reply gnek.

I found out the issue was due to my own messing with the assembly file and that I had to have:

“ax”,@progbits

after the the .itim section for this to work along with updating the .itim section to use ‘> itim AT > rom’ in the linker script