topic Re: Retain RAM data during reset on MKW38 in Kinetis Microcontrollers

Retain RAM data during reset on MKW38

xiaofenglei — Tue, 17 May 2022 02:05:19 GMT

Hello,

I'm working on MKW38 chipset, and want to keep some data in ram instead of flash when the device resets from application to bootloader side. Maybe I missed something in spec, I didn't find some special RAM related to this, and also the description about how to perform a WARM reset which is occasionally mentioned in TRM. Would you please point a way for such purpose through RAM or registers to pass some data from application to bootloader?

Thanks,

Xiaofeng

Re: Retain RAM data during reset on MKW38

xiaofenglei — Tue, 17 May 2022 20:11:52 GMT

I tried to reset with watchdog which should be usually regarded as WARM reset, but looks like the ram data is still lost during reboot.

Re: Retain RAM data during reset on MKW38

xiaofenglei — Tue, 17 May 2022 21:47:26 GMT

It's my bad, and the memory can retain content with watchdog. I will use this way.

Re: Retain RAM data during reset on MKW38

paulM90 — Thu, 15 Jun 2023 14:28:47 GMT

Ill answer here, in case somebody else bumps into this.

First, find in your reference manual a region of SRAM that remains power through a reset. In my case (mx rt 595), thats SRAM partition 0.

It's address range is:

First up, modify your linker script.

1. Add a memory region. In our case, m_persistent. I placed it at the beginning of the above-mentioned partition.

MEMORY { m_flash (RX) : ORIGIN = 0x08000000, LENGTH = 0x00300000 m_interrupts (RX) : ORIGIN = 0x00080000, LENGTH = 0x00000180 m_persistent (RW) : ORIGIN = 0x20000000, LENGTH = 0x1000 m_text (RX) : ORIGIN = 0x00080180, LENGTH = 0x7FE80 m_data (RW) : ORIGIN = 0x200C0000, LENGTH = 0x400000 m_usb_sram (RW) : ORIGIN = 0x40140000, LENGTH = 0x00004000 }

2. Add a section in the memory region.

SECTIONS { ... .persistent_data (NOLOAD) : { . = ALIGN(4); __persistent_data_start__ = .; KEEP(*(.persistent_data)) KEEP(*(.persistent_data*)) . = ALIGN(4); __persistent_data_end__ = .; } > m_persistent ... }

And place your variables in the newly created section. Here's a quick code to test the functionality. It should print the value, increment it, and reset after 3 seconds.

__attribute__((section(".persistent_data"))) int persistent_var; int main(void) { BOARD_InitPins(); BOARD_BootClockRUN(); BOARD_InitDebugConsole(); SDK_DelayAtLeastUs(1000*2500, SDK_DEVICE_MAXIMUM_CPU_CLOCK_FREQUENCY); printf("Hello World %u\n", persistent_var.PersistentValue++); NVIC_SystemReset(); }

Sample output: