To_string(double): Operator new out of memory

Mbed OS Bugs
1

I am developing for a STM32 Nucleo F103RB. This code:

#include <mbed.h>
#include <string>

BufferedSerial pc(USBTX, USBRX); // tx, rx

int main() {
  AnalogIn a1(PC_0);
  a1.set_reference_voltage(3.3);

  while(1) {
    string buf = "";
    buf = to_string(a1.read_voltage());
    pc.write(buf.c_str(), buf.length());
    wait_us(1e6);  
    }
}

causes the F103 to crash at line buf = to_string(a1.read_voltage()); with the following error message:

++ MbedOS Error Info ++
Error Status: 0x8001011F Code: 287 Module: 1
Error Message: Operator new out of memory

Location: 0x80022F9
Error Value: 0x80060E6
For more info, visit: https://mbed.com/s/error?error=0x8001011F&tgt=NUCLEO_F103RB
-- MbedOS Error Info --

the same error is thrown for code like

double val = a1.read_voltage();
buf = to_string(val);

I have similar code in an application for a STM32 F407, where no such error occurs. Is this a known issue on STM32F1s?

2 
CONFIGURATION: https://docs.platformio.org/page/boards/ststm32/nucleo_f103rb.html
PLATFORM: ST STM32 (8.0.0) > ST Nucleo F103RB
HARDWARE: STM32F103RBT6 72MHz, 20KB RAM, 128KB Flash
DEBUG: Current (stlink) On-board (stlink) External (blackmagic, jlink)
PACKAGES:
 - framework-mbed 6.60200.200722 (6.2.0)
 - tool-dfuutil 1.9.200310 
 - tool-openocd 2.1000.200628 (10.0)
 - tool-stm32duino 1.0.2
 - toolchain-gccarmnoneeabi 1.90201.191206 (9.2.1)
3

The STM32F103RB has only 20kbyte of SRAM on board. This is very little and much of it will be used by mbed-os. When you call the std::to_string function it needs to claim some work space. It looks like it wants to claim more than is available.
To solve this you can do two things: get a device with more onboard memory (STM32F103RD) or write your own to_string function which uses a buffer on the stack.

4

I know that memory on the F103RB is quite limited - but with a static memory useage of just about 10% I wasn’t expecting problems when formatting a number as a string.

RAM:   [=         ]  10.5% (used 2144 bytes from 20480 bytes)
Flash: [==        ]  23.3% (used 30532 bytes from 131072 bytes)

I have tried using sprintf() instead of to_string() and found that this produces no output for the number. for example:

char number[32];
double val = a1.read();
sprintf(number, "x %f x\n", val);

results in the string x x.
I am using the bare metal profile with std as printf lib:

{
    "requires": ["bare-metal"],
    "target_overrides": {
      "*": {
        "target.printf_lib": "std"
      }
    }
}
5

Hello Gregor,

To save memory try to enable floating point support with printf-minimal rather than with the memory hungry std. For example, in mbed_app.json:

{
    "requires": ["bare-metal"],
    "target_overrides": {
        "*": {
            "target.printf_lib": "minimal-printf",
            "platform.minimal-printf-enable-floating-point": true,
            "platform.minimal-printf-set-floating-point-max-decimals": 3
        }
    }
}

To save some additional flash memory you can try to use the small C library:

{
    "requires": ["bare-metal"],
    "target_overrides": {
        "*": {
            "target.printf_lib": "minimal-printf",
            "platform.minimal-printf-enable-floating-point": true,
            "platform.minimal-printf-set-floating-point-max-decimals": 3,
            "target.c_lib": "small"
        }
    }
}

Event queue can be handy with bare-metal too. Have a look for example at Bare-metal Event Queue with BLUEPILL.

Best regards, Zoltan

6

Bare-metal is using the small-c lib already, in the case of gcc it is newlib-nano. But the default for this lib is not to use float for printf and scanf. That must be enabled by additional Compiler Switches.
So Zoltans hint maybe a solution, but another caveat is that minimal-printf does not support precision specifiers.

7

thank you, this solves both the operator new out of memory issue and the issue of missing output of sprintf.

Interesting, do you know why this is? I cound not find any mention in the documentation. I would be ok with using the same precision setting in my whole application, but the "platform.minimal-printf-set-floating-point-max-decimals" option seems to be ignored. (also, the output is 3 decimal places regardless of "platform.minimal-printf-enable-floating-point" being set to true or false)