topic Re: NMI_b explanation in Kinetis Microcontrollers

NMI_b explanation

joeygouly — Mon, 23 Nov 2015 00:47:05 GMT

Hi all,

Just want a quick clarification about the NMI_b pin / ROM boot loader.

Imagine the MCU is powered and running, if I connect NMI_b to GND, is that all it takes to reset the MCU into the bootloader? Or do I need to pull NMI_b to GND and then RESET_b?

Hopefully an easy answer, I'm just a bit confused!

Re: NMI_b explanation

Hui_Ma — Mon, 23 Nov 2015 05:20:08 GMT

Hi,

The NMI_b pin could lead to generate a non-maskable interrupt (NMI), which could not cause chip reset.

If customer want to re-enter ROM-Bootloader, it need to using RESET_b pin.

Wish it helps.

Have a great day,
Ma Hui

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Re: NMI_b explanation

joeygouly — Mon, 23 Nov 2015 08:36:54 GMT

Hi Hui,

Is it possible with a single button like this:

If that can't I could also implement the NMI isr to generate a reset or jump to the bootloader. I would prefer a hardware solution, if it's easier.

Or perhaps I can hold NMI_b to GND with a switch, and "reset" by unplugging/plugging in the USB cable?

Please advise!

Thanks,

Joey

Re: NMI_b explanation

Hui_Ma — Mon, 23 Nov 2015 09:05:58 GMT

Hi Joey,

According to your hardware design, the chip will be reset with external RESET_b pin as expected.

I wonder why you using NMI_b pin here.

When the button was pressed/released, the NMI_b could not be recognized until the chip out of the reset process.

Customer just need RESET_b pin here.

Have a great day,
Ma Hui

Re: NMI_b explanation

joeygouly — Mon, 23 Nov 2015 09:48:51 GMT

Hi Hui,

I want to be able to put the MCU in ROM bootloader mode by pressing a button.

I'm trying to look for how to achieve this!

Thanks,

Joey

Re: NMI_b explanation

bobpaddock — Mon, 23 Nov 2015 13:00:19 GMT

Use NMI as NMI and call this function. Button bounce will probably be a problem. /* Function Pointer returning void, past void pointer: */ void (*_boot_loader_start)( void * arg ); void boot_loader_start( void ) { /* Read the function address from the ROM API tree: */ uint32_t const _boot_loader_start_address = **(uint32_t **)(0x1C00001CUL); /* Turn address in to a funciton pointer: */ _boot_loader_start = (void (*)(void * arg))_boot_loader_start_address; _boot_loader_start( NULL ); /* Call the function. Will not return from here */ } It is also possible to set up FCFG to always run the bootloader at reset which may or may not be what you really want to do.

Re: NMI_b explanation

bobpaddock — Mon, 23 Nov 2015 13:04:44 GMT

How do I get out of this brain dead editor that hoses everything into the advanced editor?

Please don't tell me to hit something in the corner, it is NOT there.

Re: NMI_b explanation

bobpaddock — Mon, 23 Nov 2015 13:08:13 GMT

Use NMI as NMI and call this function. Button bounce will probably be a problem.

/* Function Pointer returning void, past void pointer: */

void (*_boot_loader_start)( void * arg );

void boot_loader_start( void )

{

/* Read the function address from the ROM API tree: */

uint32_t const _boot_loader_start_address = **(uint32_t **)(0x1C00001CUL);

/* Turn address in to a funciton pointer: */

_boot_loader_start = (void (*)(void * arg))_boot_loader_start_address;

_boot_loader_start( NULL ); /* Call the function. Will not return from here */

}

It is also possible to set up FCFG to always run the bootloader at reset which may or may not be what you really want to do.

Re: NMI_b explanation

joeygouly — Mon, 23 Nov 2015 15:54:45 GMT

Thanks Bob, I think that's one of the solutions.

I'll probably include a RESET button on my board too.

Then I can pick from the solutions:

1) Hold NMI_b to GND and do a manual power cycle.

2) Hold NMI_b to GND and use the RESET button.

3) Make the NMI isr call the bootloader.

4) Make the NMI isr cause a reset.

Thanks!