iMXRT and HyperFlash Reset

[udoeb]

Hi,

I use an external 1V8 HyperFlash S26KS512 which is connected to FlexSPI in the same way as on the MIMXRT1050-EVKB board. I noticed that on the EVKB board the RESET input of the flash is not connected to the MCU because R169 is not placed.

I want to make sure that whenever the MCU is reset (e.g. via JTAG or from software via SYSRESETREQ) the flash is reset as well. How can I achieve that?

Can the POR_B pin act as an output as well?

Thanks.

Udo

[kerryzhou]

Hi Udo Eberhardt,

   From the HyperFlash S26KS512 reset pin description in the datsheet:

So, if you want the flash chip also be reset whenever the MCU is reset.

I think you can connect the Flash Reset pin to the MCU POR pin.

Wish it helps you!

Have a great day,
Kerry

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[udoeb]

Hi Kerry,

Thanks for your comments. However, I think the solution you proposed works only if the reset is caused by an external event such as a reset button connected to POR (and FLASH reset). In my question above I was referring to the case where the firmware resets the CPU via SYSRESETREQ bit. This is an internal reset event. In order to reset the external FLASH chip, some kind of reset output signal is needed. Is such a reset output available?

Thanks,

Udo

[kerryzhou]

Hi Udo Eberhardt,

   Today I check your question with our hardware engineer, why the R169 is not connected.

   This resistor is not connect, just make sure the hyper flash reset is not reset when the RT chip want to read the code from external hyper flash. As you know, if the code put in the hyper flash, after RT POR, the chip will run from the external hyper flash, if something else control the hyper flash reset pin to low, it will cause the code read failed.

  So, to keep safe, the hyper flash reset pin just add the pull up resistor, it will reset after flash chip POR. I don't know why you need the external flash be reset when the RT reset at the same time? You just need to make the external hyper flash works when the RT want to read it, even the RT do other reset, you don't need to reset the external flash chip.

   But if you want to reset at the same time, I have been told, when use internal software reset SYSRESETREQ, the RT POR pin will also be reset, so you can connect the external flash reset pin to POR pin.

   If you want to control the external flash reset freely, you also can use the RT GPIO pin to control it, you can find a GPIO as input pin, and in the hyper flash reset pin add an external 10k pull up resistor.

Wish it helps you!

Have a great day,
Kerry

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[udoeb]

Hi Kerry,

Thanks for your comments. I wanted to reset the HyperFlash whenever the CPU reboots (and executes ROM code) because with LPC4320 and external SPI flash I experienced issues: After a soft reset the ROM code executes but the flash is still in direct memory mode and does not respond to read ID commands issued by ROM code. ROM code hangs and the MCU does not boot. However, this was with LPC4320. I experimented a bit with the iMXRT EVAL board and found that with S26KS512 the iMXRT ROM seems to be able to identify the flash after a soft reset, even if the flash does not receive a hardware reset.

Does your statement:

"But if you want to reset at the same time, I have been told, when use internal software reset SYSRESETREQ, the RT POR pin will also be reset, so you can connect the external flash reset pin to POR pin."

mean that the POR pin is an output as well? This is not documented anywhere. Documentation should be corrected in that case.

Thanks.

Udo

[kerryzhou · Accepted solution]

Hi Udo,

   LPC4320 MCU is very old, but the RT chip is the new chip, and these two chip totally the different chip, you can find our EVK board also didn't connect the external flash reset pin, just make sure the external flash is OK to operate after POR, no matter the RT chip is reset or not.

  About the software reset, I have been told that the POR also can be output the reset signal, if you have any doubt, you can double test it on your side. From our viewpoint, you even don't need to connect the external flash reset pin to the RT POR pin, it's OK to use.

If you still have any question about it, please kindly let me know.

Have a great day,
Kerry

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[udoeb]

Hi Kerry,

Thanks for your comments. I will leave the flash reset pin unconnected, just pulled up as on the EVK.

If the POR pin can act as an output as well then this should be documented. Please improve the documentation!

Regards,

Udo

[kerryzhou]

Hi Udo,

   You are welcome.

   Thanks a lot for your suggestion.

   If you still have question about, please kindly let me know.

    If your question is solved, please help me to mark the correct answer, just to close this case, thank you!

Have a great day,
Kerry

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