i.MX ProcessorsのトピックRe: Switching boot mode without cycling power

Switching boot mode without cycling power

adevries — Tue, 01 Oct 2019 16:43:31 GMT

Hello Community,

If I wish to change the boot mode / boot configuration of the 8M Mini, is it necessary to power the processor down completely before doing so? Or is it acceptable to simply assert signal POR_B, change the BOOT_MODE and BOOT_CFG pins, and then de-assert signal POR_B?

Also, is it necessary for BOOT_MODE, TEST_MODE, and other boot configuration inputs to be pulled high or low through a resistor? Or can the inputs be tied directly to NVCC_JTAG or GND?

Thanks

Re: Switching boot mode without cycling power

igorpadykov — Tue, 01 Oct 2019 23:56:18 GMT

Hi adevries

yes in general it is sufficient to assert signal POR_B for changing processor boot mode / boot configuration.

>is it necessary for BOOT_MODE, TEST_MODE, and other boot configuration inputs

>to be pulled high or low through a resistor? Or can the inputs be tied directly to NVCC_JTAG or GND?

recommended to use resistors as before processor is fully powered-up, internal logic controlling

the input connection circuits is not initiated, so there may be leakage through boot configuration inputs.

Best regards
igor

Re: Switching boot mode without cycling power

adevries — Wed, 02 Oct 2019 02:09:46 GMT

Hi Igor,

I know the recommendation is to normally use resistors, but I've got an application where I'm looking to temporarily override what the pin is pulled to. For example, if I normally have BOOT_MODE1 set to 0 by pulling it down to GND through a 100k resistor, I'm looking to temporarily set it to 1 by connecting the pin to NVCC_JTAG.

recommended to use resistors as before processor is fully powered-up, internal logic controlling
the input connection circuits is not initiated, so there may be leakage through boot configuration inputs.

Will the leakage through the pins be limited to the leakage parameters listed in Table 20 and 21 of the i.MX 8M Mini Datasheet?

Re: Switching boot mode without cycling power

igorpadykov — Wed, 02 Oct 2019 04:57:17 GMT

Hi adevries

>Will the leakage through the pins be limited to the leakage parameters

>listed in Table 20 and 21 of the i.MX 8M Mini Datasheet?

not. Unfortunately they are not specified.

Best regards
igor

Re: Switching boot mode without cycling power

adevries — Wed, 02 Oct 2019 17:08:24 GMT

Hi Igor,

That is very good to know. Since there must be a resistor to control the leakage, current, could you recommend what value resistor I should use?

In the image below, I have BOOT_MODE1 pulled high to NVCC_JTAG with a 4.7k resistor. I'm looking to temporarily override that and pull it low with a stronger resistor. What value would you recommend?

Thanks

Re: Switching boot mode without cycling power

igorpadykov — Wed, 02 Oct 2019 23:34:30 GMT

Hi adevries

general recommendation is to follow nxp i.MX8MMini reference schematic

i.MX 8M Mini Evaluation Kit LPDDR4 Design Files

and

i.MX 8M Mini Hardware Developer’s Guide

p.14 SPF-31407 BaseBoard schematic gives similar example for overriding boot resistors.

Best regards
igor

Re: Switching boot mode without cycling power

adevries — Thu, 03 Oct 2019 16:49:45 GMT

Hi Igor,

Okay, thanks for the recommendation. I'll adjust my design to more closely follow the baseboard schematic.

Thanks