LPC5506 SCB AIRCR SYSRESETREQ bitmask sets RAM to 0

[embeddeddavid]

Hi!

I am currently working with an LPC5506. When __NVIC_SystemReset() is called a certain SRAM0 addres range is set to 0. I have observed this happens, at least in the 0x2000_1740 -0x2000_17BF range.

This does have nothing to do with zero fill the bss segment in the ResetISR() function, since our application does not initialize the bss section (this is done intentionally).

I have read the boot code in ROM may change the SRAM data. Therefore, I have used blhost to check property 12. The whole range 0x2000_000 – 0x2000_7FFF is mentioned (32 kB). However, I have observed that only certain addresses are set to 0.

Our application initializes most of the variables after a reset (no matter whether a SW reset, POR, etc.). However, there’s certain data we want to preserve on a SW reset. We're aware of the RTC general purpose registers, however, we would like to preserve more than 32 bytes of data. Are there any other means of doing this? Has someone experienced the same issue?

Thanks in advance.

[Alice_Yang]

Hello embeddeddavid ,

Yes, some RAM memory are reserved  by ROM initialization.

About the ROM reserved regions , you can obtained from the blhost command "get-property 12":

BR

Alice

[embeddeddavid]

Hi Clemens,

As you can see in the attached image, the code in ROM also reserves SRAM 1, 2 or 3 for its own use. We are also developing some applications for a LPC55S69 and we have not experienced this issue even though the ROM bootloader theoretically also reserves the RAM. It is kind f a lottery. It would be desireable to achieve some certainty instead of trial and error.

Regards,

[cgerlach]

Hi,

hmm, can't see that. In the attached image it claims:

0x300000000 - 0x30007ffff (SRAM 0, secure access)
0x200000000 - 0x20007ffff (SRAM 0, non-secure access)
0x40000000 - 0x40003fff (SRAM X, non-secure access)
0x140000000 - 0x140001fff (part of SRAM X, secure access)

I do not see SRAM above 0x20008000 being claimed.

(Referring to UM11424, Rev. 1.3, Ch 2.1.5)

Am I missing something?

[embeddeddavid]

Nope, Clemens, you are totally right. I misled the memory addresses.

I will ask my colleagues if this might be an option.

Thanks a lot.

[cgerlach · Accepted solution]

Hi,

the LPC5506 has 96k of RAM in total (I know, including SRAM X). Have you tried using SRAM 1,2 or 3 (i.e. a RAM address between 0x30008000 and 0x30013FFF)?

As I will have to do the same programming in a short while I had that in the back of my mind, thus I am curious.

Regards,

Clemens

[RudeOstrich]

I have same question and didn't get satisfied solution. 

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