Enter DFU mode with stm32F401 (bootloader Issue)

[devHAA]

Description

Hello,

I'm having troubles with mbed-os 5. With the previous version of mbed (v163) it worked perfectly. With the following piece of assembler code, the micro (stm32F401) enters DFU mode. But with the newest version of mbed-os 5 (5.10.2) doesn't work.

• Target: NUCLEO-F401RE
• Toolchain: GCC_ARM (7 2018-q2-update)
• Using eclipse + mbed-cli (v1.8.2)
• Mbed OS (5.10.2)

void enterDFU(){

__asm ("LDR     R0, =0x40023844");// RCC_APB2ENR
__asm ("LDR     R1, =0x00004000");// ENABLE SYSCFG CLOCK
__asm ("STR     R1, [R0, #0]");

__asm ("LDR     R0, =0x40013800");// remap ROM at zero
__asm ("LDR     R1, =0x00000001");// SYSCFG_MEMRMP
__asm ("STR     R1, [R0, #0]");

__asm ("LDR     R0, =0x1FFF0000");// ROM BASE
__asm ("LDR     SP,[R0, #0]");    // SP @ +0
__asm ("LDR     R0,[R0, #4]");    // PC @ +4

__asm ("BX      R0");             // Jump to Bootloader
}

I've been doing some tests and I think that the problem is in the last line __asm ("BX R0"); , when it should jump to the Bootloader. If I try to connect the device on the PC it says "descriptor request error".

Any ideas what may be happening, Thank you.

Issue request type

[ ] Question
[ ] Enhancement
[x] Bug

[0xc0170]

Just to be certain - you are using f401 with v163 (mbed 2 version), not Mbed OS 5.10.2 ?

@ARMmbed/team-st-mcd Please review

[devHAA]

Just to be certain - you are using f401 with v163 (mbed 2 version), not Mbed OS 5.10.2 ?

@ARMmbed/team-st-mcd Please review

Yes @0xc0170, the version that works is mbed 2 (v163), and the version that doesn't work is mbed-os 5.10.2.

Thank you for your quick reply.

[0xc0170]

Can you compare R0 value before and now? What toolchain - using online compiler?

I reviewed quickly recent changes , only change there was alignment for ARMCC change (affects RAM to be aligned to 8 byte). That should not have any affect to this issue.

If I try to connect the device on the PC it says "descriptor request error".

Look at ST forum to find some help - missing driver for instance?

[devHAA]

Can you compare R0 value before and now? What toolchain - using online compiler?

I'm using eclipse with GCC_ARM compiler. In the online compiler the __asm is not recognized. The compiler error says "Expected an expression "__asm ("LDR R0, =0x40023844");"

I'm trying to see how to read R0 in c++, when I know how to do it I'll post it here

Look at ST forum to find some help - missing driver for instance?

This is not the problem, because as I said, with mbed 2 (v163) it works, and the PC takes the proper driver because the driver is installed.

[0xc0170]

I'm using eclipse with GCC_ARM compiler. In the online compiler the __asm is not recognized. The compiler error says "Expected an expression "__asm ("LDR R0, =0x40023844");"

This code snippet from the mbed_application can help you: https://github.com/ARMmbed/mbed-os/blob/master/platform/mbed_application.c#L143 (using inline asm for ARMCC - the first one, later is for GCC and IAR).
You can debug your app and set a breakpoint to verify the last 4 instructions at least (I wonder what has changed on that address and then what you are loading to SP,PC and R0).

This is not the problem, because as I said, with mbed 2 (v163) it works, and the PC takes the proper driver because the driver is installed.

OK, might be the board is in bad state and cant connect.

[devHAA]

OK, might be the board is in bad state and cant connect.

I just tried this simple example with the same board (NUCLEO-F401RE), using mbed 2 (v163), and then mbed-os 5.10.2. Both with the online compiler.

#include "mbed.h"

#if defined(__CC_ARM)
    __asm static void enterDFU(){
        LDR     R0, =0x40023844
        LDR     R1, =0x00004000
        STR     R1, [R0, #0]
        
        LDR     R0, =0x40013800
        LDR     R1, =0x00000001
        STR     R1, [R0, #0]
        
        LDR     R0, =0x1FFF0000
        LDR     SP,[R0, #0]
        LDR     R0,[R0, #4]
        BX      R0
    }
#endif

int main() {     
    enterDFU();  
}

With the mbed 2 (v163) it works perfect (PC recognized it as STM Device in DFU Mode), but with mbed-os 5.10.2 doesn't work. It says Unknown USB Device (Device Descriptor Request Failed)