nRF51 RAM retention after System Reset question.

[Valer_I]

Hello, I looked througth the devzone but didn't find direct answer. So created new one.

RM v3.0 states chapter 12.1.19 "Reset behavior" with table. However, it is not clear for me what crosses in table mean. In general, I want to use filled data array in RAM after calling NVIC_SystemReset(). I use softdevice and tried to do next:

uint32_t ramon_all= POWER_RAMON_ONRAM0_RAM0On  << POWER_RAMON_ONRAM0_Pos
                     | POWER_RAMON_ONRAM1_RAM1On  << POWER_RAMON_ONRAM1_Pos
                     | POWER_RAMON_OFFRAM0_RAM0On  << POWER_RAMON_OFFRAM0_Pos
                     | POWER_RAMON_OFFRAM1_RAM1On  << POWER_RAMON_OFFRAM1_Pos;
 static uint8_t myarray[64] __attribute__( ( section( "NoInit"), zero_init) ); //place it to NoInit section.
sd_softdevice_enable(...);
...
memset(myarray,0xA5,64);
...
uint32_t res=sd_power_ramon_set(ramon_all);  //check result
uint32_t ramon; 
res=sd_power_ramon_get(&ramon); //check result and value
sd_nvic_SystemReset();

After reset myarray filled with zeros.
The questions:

1. Is RAM retention possible at system reset. If yes, how to make it possible or what is wrong in my code?

2. What the link of NVIC_SystemReset(); in code with Table 12.1.19 "Reset behaviorchapter" in RM ? Does NVIC_SystemReset perform soft reset?

P.S. These threads helped me, but partially. Link , Link

[Håkon Alseth]

Hi,

I believe you're "almost" there. I suspect that you've not set "NoInit" on the RAM-block in your settings. A "Soft reset" is the same as doing a nvic_systemreset(); and it shall not clear your RAM as per our datasheet (be aware that the startup file may do so anyway!)

Attached is a modified example (based on SDK11) that shows how to utilize this in a simple manner.

ram_retention_example.zip

Cheers, Håkon