Time functions are broken on bluepill_f103c8 (mbed)

1

The Time functions does not work on bluepill_f103c8, seems to always return -1. Functions are tested with the example code on their website https://os.mbed.com/docs/latest/reference/time.html

Version: Home 0.9.3 Core 3.5.3a8
IDE: Atom
OS: Windows10

Main:

#include "mbed.h"


Serial pc(B6,B7,57600);//TX, RX,BAUD RATE


int main()
{
    pc.printf("START\n");
    set_time(1256729737);  // Set RTC time to Wed, 28 Oct 2009 11:35:37
        while (true)
        {
            time_t seconds = time(NULL);

            pc.printf("Time as seconds since January 1, 1970 = %d\n", seconds);

            pc.printf("Time as a basic string = %s", ctime(&seconds));

            char buffer[32];
            strftime(buffer, 32, "%I:%M %p\n", localtime(&seconds));
            pc.printf("Time as a custom formatted string = %s", buffer);
            pc.printf("\n");
            wait(1);
        }
}

platformio.ini:

[env:bluepill_f103c8]
platform = ststm32
board = bluepill_f103c8
framework = mbed
2

Yep this doesn’t work. When you debug it you’ll see that when you go the time function, mbedos tries to use the _rtc_read read function but that is NULL.

debugging_stm32
debugging_stm32618×503 20.5 KB

These RTC functions are usually set by calling attach_rtc(time_t (*read_rtc)(void), void (*write_rtc)(time_t), void (*init_rtc)(void), int (*isenabled_rtc)(void)), but somehow this not done for this board / platform.

I’ll see where I can find the needed functions. The STM32F103C8 does have an RTC, you just need to call into the STM32HAL functions to use it.

3

Well, that was easy. The RTC API is implemented in targets/TARGET_STM/rtc_api.c. It is guarded by the macro


#if DEVICE_RTC
//entire code..

And that macro wasn’t set. Defining this macro activates the RTC functionality and auto-initializes everything (no need to call attach_rtc yourself) Go to your platformio.ini and add as a build flag:

build_flags = -DDEVICE_RTC=1

Your program will then output

START
Time as seconds since January 1, 1970 = 1256729737
Time as a basic string = Wed Oct 28 11:35:37 2009
Time as a custom formatted string = 11:35 AM

Tested this on my own Bluepill board.

2 Likes
4

Thank you, i just verified this on my blue pill and it indeed works.
I raised an issue in the STM32 github to see what they think about it but no response so far

5

Hi @OscarGarciaF! How did you enable bluepill board in the mbed online compiler? I can’t find this board in platform list to reproduce the issue.

6

it’s not oficially supported. check here it provides a workaround to use it

7

Hm, I don’t know the reason, but the RTC module is disabled in the configuration for the bluepill board in the official mbed repository. So there are 2 options: add build_flags = -DDEVICE_RTC=1 to your platformio.ini or use nucleo_f103rb board.

8

Hi build_flags = -DDEVICE_RTC=1 do works as @maxgerhardt indicated above