What I was doing
I am using a STM32 microcontroller and for my project I need to be able to send data at specific times of the day (say, at 11am and 2pm). The microcontroller needs to know what time it is before I can achieve this. Unfortunately, I only have an one-way communication, and I therefore cannot request the current time from the network.
Therefore I want to set the current time, directly after I am done programming. I knew I am able to write data to the flash using the ST-LINK Utility Command Line Interface (ST-LINK_CLI) using the following command:
ST-LINK_CLI.exe -w32 <Address> <data> -Rst
I wrote a simple test script that writes the Unix time stamp to some address not currently in use by the code.
I was about to write a function to read the time-stamp and use it to set the RTC time. Until I read the following in the ST-LINK Utility User Manual:
-w32 supports writing to Flash memory, OTP, SRAM and R/W registers.
When the manual says it supports writing to the R/W registers, does this mean I can directly access the RTC registers and set them? I have tried, but I can't seem to write to these registers.
I would prefer to use this method if it does, as I would not need to write a specific function to handle it on the microcontroller anymore. This means that I can set the RTC time of any microcontroller we currently have in use, instead of needing to update their code.
What I intended to do
To set the RTC registers, I tried to do the following steps, as described in the STM Reference Manual:
- set DPB bit in PWR_CR register
- write 0xCA to RTC_WPR register
- write 0x53 to RTC_WPR register
- stop the RTC by setting the INIT bit in RTC_ISR register
- select the 1Hz clock by writing to the RTC_PRER register
- load the current time by writing to the RTC_TR register
- load the current date by writing to the RTC_DR register
- start the RTC by resetting the INIT bit in RTC_ISR register
To access the registers, I have used the following addresses:
- PWR_CR: 0x4000 7000
- RTC_WPR: 0x4000 2824
- RTC_ISR: 0x4000 280C
- RTC_PRER: 0x4000 2810
- RTC_TR: 0x4000 2800
- RTC_DR: 0x4000 2804
What went wrong
I am not able to write to either of these registers. With the ST-LINK Utility, I get the following message:
Error occured during memory writing!
Using the ST-LINK_CLI:
Writing 0x00000100 at 0x40007000...Error!
Reading these registers is no problem, but I cannot write to them using either the ST-LINK Utility or its Command Line Interface.
How can I write to the R/W registers using the ST-LINK Utility?
Is there some kind of write protect to allow writing to the RTC registers which I overlooked?