topic Re: LPC55 sprintf float values in LPC Microcontrollers

LPC55 sprintf float values

SvenAsbach — Wed, 27 Aug 2025 08:37:07 GMT

Hi community,
I am trying to setup sprintf to print float numbers to string.
I tried everything I found, changed libraries, but nothing brought a success.
Either I get not the right result or I get an hardfault when trying to print negative float values.

Actual processor LPC5506
Floating point unit FPv5-SP-D16 Hard ABI set
current library setting Redlib semihost
I am using UART0 to print

PreProcessor settings
CPU_LPC5506JBD64
CPU_LPC5506JBD64_cm33
SDK_OS_BAREMETAL
SDK_DEBUGCONSOLE=2
SERIAL_PORT_TYPE_UART=1
PRINTF_FLOAT_ENABLE=1
SCANF_FLOAT_ENABLE=1
PRINTF_ADVANCED_ENABLE=1
SCANF_ADVANCED_ENABLE=1
__MCUXPRESSO
__USE_CMSIS
DEBUG
DISABLEFLOAT16
__REDLIB__

trying this code

float P_Value = 3.123456f;

float I_Value = 123.4567f;

float D_Value = 0.654321f;

sprintf(g_txBuffer, "rpm = %d, P_Value = %f, I_Value = %f, D_Value = %f \r", rpm_ist, P_Value, I_Value, D_Value);

no warnings or errors

And the result is
rpm = 206, P_Value = -0.000000, I_Value = -0.000000, D_Value = -0.000000 <CR>

Is there a way to get sprintf to print the right values including negative values or do I have to write my own converter?
What I do not see?

Thanks in advance

Re: LPC55 sprintf float values

ErichStyger — Wed, 27 Aug 2025 10:42:23 GMT

Usually the problem is that CR_INTEGER_PRINTF is still defined in the -D options list.

Make sure you do a full 'clean' of the build an retry.

These are my (working) defines and Linker settings:

__REDLIB__
CPU_LPC55S69JBD100
CPU_LPC55S69JBD100_cm33
CPU_LPC55S69JBD100_cm33_core0
SDK_DEBUGCONSOLE=1
PRINTF_FLOAT_ENABLE=1
SERIAL_PORT_TYPE_UART=1
__MCUXPRESSO
__USE_CMSIS
DEBUG

I hope this helps,

Erich

Re: LPC55 sprintf float values

ZhangJennie — Wed, 27 Aug 2025 10:49:22 GMT

Hi @SvenAsbach

If you use SDK demo, please try to enable floating support

Make sure the defined symbols, printf float is enabled.

Does this work for you?

Best Regards

Jun Zhang

Re: LPC55 sprintf float values

SvenAsbach — Wed, 27 Aug 2025 11:15:54 GMT

Thanks for the fast answer, but this does not help.
All what you are proposing is already set and tried, but no success.
Compiler uses this

arm-none-eabi-gcc -DCPU_LPC5506JBD64 -DCPU_LPC5506JBD64_cm33 -DSDK_OS_BAREMETAL -DSDK_DEBUGCONSOLE=2 -DSERIAL_PORT_TYPE_UART=1 -DPRINTF_FLOAT_ENABLE=1 -DSCANF_FLOAT_ENABLE=1 -DPRINTF_ADVANCED_ENABLE=1 -DSCANF_ADVANCED_ENABLE=1 -D__MCUXPRESSO -D__USE_CMSIS -DDEBUG -DDISABLEFLOAT16 -D__REDLIB__ -I"D:\Software\FC5706P_workspace\FC5706P101B001\drivers" -I"D:\Software\FC5706P_workspace\FC5706P101B001\device" -I"D:\Software\FC5706P_workspace\FC5706P101B001\component\serial_manager" -I"D:\Software\FC5706P_workspace\FC5706P101B001\utilities" -I"D:\Software\FC5706P_workspace\FC5706P101B001\component\uart" -I"D:\Software\FC5706P_workspace\FC5706P101B001\CMSIS" -I"D:\Software\FC5706P_workspace\FC5706P101B001\component\lists" -I"D:\Software\FC5706P_workspace\FC5706P101B001\CMSIS_driver\Include" -I"D:\Software\FC5706P_workspace\FC5706P101B001\CMSIS\DSP\Include" -I"D:\Software\FC5706P_workspace\FC5706P101B001\CMSIS\DSP\PrivateInclude" -I"D:\Software\FC5706P_workspace\FC5706P101B001\CMSIS\DSP\Source\DistanceFunctions" -I"D:\Software\FC5706P_workspace\FC5706P101B001\CMSIS\NN\Include" -I"D:\Software\FC5706P_workspace\FC5706P101B001\board" -I"D:\Software\FC5706P_workspace\FC5706P101B001\source" -O0 -fno-common -g3 -gdwarf-4 -Wall -c -ffunction-sections -fdata-sections -fno-builtin -fmerge-constants -fmacro-prefix-map="../CMSIS/DSP/Source/BasicMathFunctions/"= -mcpu=cortex-m33 -mfpu=fpv5-sp-d16 -mfloat-abi=hard -mthumb -D__REDLIB__ -fstack-usage -specs=redlib.specs -MMD -MP -MF"CMSIS/DSP/Source/BasicMathFunctions/BasicMathFunctionsF16.d" -MT"CMSIS/DSP/Source/BasicMathFunctions/BasicMathFunctionsF16.o" -MT"CMSIS/DSP/Source/BasicMathFunctions/BasicMathFunctionsF16.d" -o "CMSIS/DSP/Source/BasicMathFunctions/BasicMathFunctionsF16.o" "../CMSIS/DSP/Source/BasicMathFunctions/BasicMathFunctionsF16.c"

Re: LPC55 sprintf float values

ZhangJennie — Mon, 01 Sep 2025 08:08:26 GMT

Hi @SvenAsbach

Did you include "stdio.h"? We need to make sure we have this header file included.

I just tested sprintf with your code, there is no issue on my side. See attached video.

Please also make sure you use floating point version of printf.

Can you please checking your issue with refering my screenshot and testing video?

Best Regards

Jun Zhang

Re: LPC55 sprintf float values

SvenAsbach — Fri, 05 Sep 2025 06:31:49 GMT

Stdio.h is included and used.

Where can I check in an existing project that the right printf version is used or where do I change it?
My preprocessor settings I have already send to you.

CR_INTEGER_PRINTF is not used in the build

Build is done with

Re: LPC55 sprintf float values

ZhangJennie — Wed, 10 Sep 2025 07:31:34 GMT

Hi @SvenAsbach

Please make sure the project defined symbols and floating point set as below:

Hope this helps,

Jun Zhang