imx rt 1024 position independent code part 2

[bp1979]

I had a question open which was perfectly solved in this Q&A .

As mentioned in my last comment, I didn't bring me a whole lot further. When I include freertos into my program, I get a mem fault when the first tasks is started when I compile with -fpic.

When I recompile without -fpic, the blink test runs fine. 

I added two projects to this issue:

- MIMXRT1024_Project.zip : the project compiled WITH -fpic, which crashes on mem fault

- MIMXRT1024_Project.zip: the project compiled normally, without -fpic. Runs fine.

I would be very very grateful if you could help me and explain what I am doing wrong. I have tried so many things but I am getting nowhere. Moving got to ITC sram. DTC sram. Moving vector table into ITC/DTC sram. Leaving .got in flash. Nothing gives. I have the feeling that I am so close to a working solution, but I just can't find the culprit.... 

[jingpan]

Hi @bp1979 ,

I haven't RT1024 board on hand. I only have a RT1064-EVK. So, I made a led-blinky demo. I put .got in flash. You can trace if R9 is really correct by stop at RestISR().

And please check if vector table is at right position.

Regards,

Jing

[bp1979]

Hi @jingpan

The problem comes when i use freertos. Just blinking the pin already worked.

Could you try the project i attached and swap the cpu to whatever you have lying around there? 

[jingpan · Accepted solution]

Hi @bp1979 ,

FreeRTOS will flush all CPU register by kernel, include R9. This is happened in first time start the task.

void vPortSVCHandler( void )
{
    __asm volatile (
        "	ldr	r3, pxCurrentTCBConst2		\n"/* Restore the context. */
        "	ldr r1, [r3]					\n"/* Use pxCurrentTCBConst to get the pxCurrentTCB address. */
        "	ldr r0, [r1]					\n"/* The first item in pxCurrentTCB is the task top of stack. */
        "	ldmia r0!, {r4-r11, r14}		\n"/* Pop the registers that are not automatically saved on exception entry and the critical nesting count. */
        "	msr psp, r0						\n"/* Restore the task stack pointer. */
        "	isb								\n"
        "	mov r0, #0 						\n"
        "	msr	basepri, r0					\n"
        "	bx r14							\n"
        "									\n"
        "	.align 4						\n"
        "pxCurrentTCBConst2: .word pxCurrentTCB				\n"
        );
}

If without -fPIC, R9 is not used. So, this will not cause any problem. But if compile with -fPIC, R9 is used.  So, you must recover R9.

Regards,

Jing

[bp1979]

@jingpan thx. Already figured it out with help from freertos forum. Forgot to reply here. Thx though.! 

The biggest problem i now have is debugging my app while offset in flash. I have another questions open for that. Would be really great if sonebody could help there.