topic Re: KW45 noinit ram section in MCUXpresso SDK

KW45 noinit ram section

jiajun_cheng — Fri, 28 Nov 2025 07:38:47 GMT

Hi,nxp Expert：
I want to isolate a portion of RAM in kw45 for storing some flags. However, currently when I try to write 0xa5a5a5a5 to address 0x02000000 and then perform a soft reset, the value read from address 0x02000000 after the reset is 0. Could you please help me figure out how to ensure that the value read after the soft reset remains the same as before the reset?

Re: KW45 noinit ram section

Christine_Li — Fri, 28 Nov 2025 09:54:59 GMT

Hi, @jiajun_cheng

The last 8 KB RAM (0x2001_A000) is from independent power switch domain which can keep data retention in all power modes.

For details, please refer to KW45 Reference Manual

Please let me know whether have any other concerns on this case.

Otherwise, please do not hesitate to mark my answer as a solution, so that we can close this case.

Best regards,

Christine.

Re: KW45 noinit ram section

jiajun_cheng — Sun, 30 Nov 2025 13:06:07 GMT

Hi, @Christine_Li :

However, I noticed this section of code again in the startup file startup_KW45B41Z83.S—doesn’t it clear the memory range from 0x2001_A000 to 0x2001_C000?

.ram_init_stcm5: ldr r0, =0x2001a000 ldr r1, =0x2001c000 .loop5: /* Initialize stcm5 */ stmia r0!, {r2 - r5} cmp r0, r1 bcc.n .loop5

Re: KW45 noinit ram section

Christine_Li — Mon, 01 Dec 2025 06:15:33 GMT

Hi， @jiajun_cheng

From the code side, you are right, it will clear this area.

You need to modify, and not perform any write operations to this region during startup.

Below is my suggestions:

1.remove this initialization for the retention RAM section.

2. You can keep those loops but skip the retention RAM range.

3. Ensure the initialization table does not include the retention RAM region at all.

Please let me know whether have any other concerns on this case.

Best regards,

Christine.

Re: KW45 noinit ram section

Christine_Li — Wed, 03 Dec 2025 02:38:18 GMT

Hi, @jiajun_cheng

Anything else I can do for you on this case?

Best regards,

Christine.