how can I retain RAM after watchdog reset and bootloader present

RE: how can I retain RAM after watchdog reset and bootloader present

Einar Thorsrud — Wed, 02 Mar 2016 08:17:48 GMT

I have updated the answer to cover the situation where you use a bootloader.

RE: how can I retain RAM after watchdog reset and bootloader present

makouda — Tue, 01 Mar 2016 13:26:52 GMT

I noticed that when I keep above variable out of bootloader RAM range it works fine. is that mean that the RAM is affected by the bootlader even when the bootloader is not running???

bootloader RAM configuration

RE: how can I retain RAM after watchdog reset and bootloader present

makouda — Mon, 29 Feb 2016 13:15:14 GMT

I noticed that when I dont use boot loader, it's working (RAM retention working) but when I flash the bootloader, it's not working. what could be the problem

RE: how can I retain RAM after watchdog reset and bootloader present

RK — Sat, 27 Feb 2016 03:30:44 GMT

.. comment removed as I now see two different loads of documentation about what 'zero_init' means.

RE: how can I retain RAM after watchdog reset and bootloader present

Einar Thorsrud — Fri, 26 Feb 2016 13:55:44 GMT

Please refer to this answer to a very similar question.

The suggested solution for that case does not work for you, but the initial part of the answer is: the reset behavior table found in section 12.1.19 of the nRF51 RM states that RAM content may be corrupted for all reset sources but CPU lockup and softreset. This means that even if you do everything by the book with regard to RAM retention, you still risk the data being corrupted after a watchdog reset. So what you ask is not possible on the nRF51 HW, as you cannot be confident that RAM data is valid after a watchdog reset.

Your updated question asks about differenced using bootloader or not. The bootloader is always run at startup if it is flashed, though it will not do much in the normal case where there is no upgrade ongoing. It will do some basic configuration (configure LED's, enable timer and GPIO for button etc) and check whether it is in the process of upgrading or not, and if there is a valid application. Then it will start the application. This means that you risk losing data that is stored in the RAM area for the bootloader, also when not upgrading.

So in your case you have two separate issues that can make your data corrup:

RAM content may be corrupted after watchdog reset
Bootloader will use some of it's RAM at startup even if no upgrade is ongoing.

RE: how can I retain RAM after watchdog reset and bootloader present

Wojtek — Thu, 25 Feb 2016 09:50:20 GMT

I am not sure, but additionally to things you implemented (modified .sct file and attribute) I also have "NoInit" for IRAM2 ticked in "target" tab in target options in keil. Maybe you could try that.