Help on Assembly for Cortex-M0/M0+

[kai_liu]

I am upgrading AN4379 MSD bootloader from K60 to FRDM-KL25Z. Here is the code snippet.

void Switch_mode(void)

{

     volatile uint_32  temp = 1;   /* default the button is not pressed */

     /* Get PC and SP of application region */

    New_sp  = ((uint_32_ptr)IMAGE_ADDR)[0];

    New_pc  = ((uint_32_ptr)IMAGE_ADDR)[1];

    if(temp)

    {

        if((New_sp != 0xffffffff)&&(New_pc != 0xffffffff))

        {

            /* Run the application */

#if (!defined __MK_xxx_H__)

     /* */

            asm

            {

                move.w   #0x2700,sr

                move.l   New_sp,a0

                move.l   New_pc,a1

                move.l   a0,a7

                jmp     (a1)

            }

#elif defined(__CWCC__)

            asm

            {

                ldr   r4,=New_sp

                ldr   sp, [r4]

                ldr   r4,=New_pc

                ldr   r5, [r4]

                blx   r5

            }

#elif defined(__IAR_SYSTEMS_ICC__)

#if defined (MCU_MKL25Z4)

            asm("msr    msp, New_sp");

            asm("msr    psp, New_sp");

            asm("mov    r5, New_pc");

            asm("mov    pc, r5");

#else           

            asm("mov32   r4,New_sp");

            asm("ldr     sp,[r4]");

            asm("mov32   r4,New_pc");

            asm("ldr     r5, [r4]");

            asm("blx     r5");

#endif           

#endif /* end (!defined __MK_xxx_H__) */

        } /* EndIf */

    }

}

But IAR reports my assembly is wrong.

Does anyone can recommend some assembly language covering Cortex-M0? Although we are working on high level language. Sometimes assembly programming is still very useful in highly optimized code and libraries.

[Kan_Li]

Hi Kai,

You may add the following assembly code in your project.

; AREA   CortexMx, CODE, READONLY      ; name

    SECTION .noinit : CODE (2)

  PUBLIC boot_app

;New_sp: r0

;New_pc: r1

boot_app:

  ;PUSH     {LR}

  msr      msp,r0  ;//set SP

  blx      r1       ;//run!

  POP      {PC}

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

  END

and modify your code like the following:

#elif defined(__IAR_SYSTEMS_ICC__)

#if defined (MCU_MKL25Z4)

            boot_app(New_sp,New_pc);

#else          

            asm("mov32   r4,New_sp");

            asm("ldr     sp,[r4]");

            asm("mov32   r4,New_pc");

            asm("ldr     r5, [r4]");

            asm("blx     r5");

#endif          

Hope that helps,

B.R

Kan

[kai_liu]

Thank you. Kan.

Actually I have followed the another solution available from other bootloader project. Which uses R0/R1 as params' carriers.

#if defined (MCU_MKL25Z4)     

            JumpToUserApplication(New_sp,New_pc);

#else           

...

static void JumpToUserApplication(LWord userSP, LWord userStartup)

{

  // set up stack pointer

  __asm("msr msp, r0");

  __asm("msr psp, r0");

  // Jump to PC (r1)

  __asm("mov pc, r1");

}

In early 8051 age, and other highly optimized DSP application, assembly is a must. It seems even in ARM world assembly sometimes very important as well.

Do you know any resources introduce Cortex-M0/M0+/M3/M4 assembly language?

[Kan_Li · Accepted solution]

Hi Kai,

Please kindly refer to the following attachment for details.

Hope that helps,

B.R

Kan

[kai_liu]

Hi, Kan Li

I have an issue related to this topic. The bootloader I developed Any update fro AN4379 MSD device bootloader? can download firmware correctly, which is verified by inspecting via memory window, it can jumps to user application. But the user application (FRDM-KL25ZDemo-blinky) doesn't work.

So either user application, or bootloader has some bugs.

I load re-directed user application in FRDM, runs from 0x8000. The demo works.

What's going on here? In principle, only three elements are important: SP/PC.

SP: Same before redirect vectors: 0x20002FF8

PC: redirected, from 0x0000 to 0x8000

Maybe I got some confusion here. Please give me some directions. I will compare the AN2295 bootloader with AN4379 as well as cross-check.

[Kan_Li]

Hi Kai,

I am suspecting if the "JumpToUserApplication(New_sp,New_pc);" you are using has some problem. Would you please try my code instead to see if any difference would be made. Thanks for your patience!

Hope that helps,

B.R

Kan

[kai_liu]

Hi, Kan,

I have found the root cause. Maybe we can not call it as the root cause, since I have not traced down to register level.

In my bootloader, I init MCG before GPIO(push button+LED) , timer and UART and control transfering to user application, since I though MCG is critical for all the modules. And MCG is configured as USB device.

In my user application, there is another USB CDC application, so the MCG is configured as USB device as well.

If bootloader jumps to user application, then MCG has been configured twice. And for some reason, it returns as 0x01 from pll_init( ), as FEI ?

Then I swap the init order, I init GPIO at very beginning without MCG init and jumps to user application. It works now.

BTW, now I use your code. I found it is available from AN4370 USB DFU bootloader.

Now I prepare a document for updated AN4379 bootloader at https://community.freescale.com/docs/DOC-97782.

[kai_liu]

Thanks

I will spend my hours on them.

Kan.