Posted on October 16, 2013 at 20:18
Hello,
I'm currently working on a motor application where i need to perform some simple math but at a high rate (20khz). Unfortunately, for some reason the computation time is too long, and it is unable to keep up with the update rate.
I measured the number of cycles for a simple line such as:
Angle = (float)(Count)*COUNT2ANGLE + THETA_ZERO;
Where COUNT2ANGLE andTHETA_ZERO are floating point constants (using defines). This line requires 200 cycles which is just way too long. Here is the disassembly of the line of code:
208 Angle = (float)(Count)*COUNT2ANGLE + THETA_ZERO;
08000d96: uxth r2, r0
08000d98: vmov s15, r2
08000d9c: vcvt.fu32 s0, s15
08000da0: vmov r0, s0
08000da4: bl 0x80004a4 <
__extendsfdf2
>
08000da8: add r3, pc, #60 ; (adr r3, 0x8000de8 <
TIM1_UP_TIM16_IRQHandler
+120>)
08000daa: ldrd r2, r3, [r3]
08000dae: bl 0x800054c <
__muldf3
>
08000db2: add r3, pc, #60 ; (adr r3, 0x8000df0 <
TIM1_UP_TIM16_IRQHandler
+128>)
08000db4: ldrd r2, r3, [r3]
08000db8: bl 0x80001e8 <
__aeabi_dadd
>
08000dbc: bl 0x80009c0 <
__truncdfsf2
>
What i don't understand is why are there calls to
__extendsfdf2 fd
, etc. which are floating point emulation functions? its seems the compiler is mixing soft and hard floating point instructions.
Im using Atollic (GCC) with the the following compiling options:
-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -std=gnu90 -DSTM32F30X -DUSE_STDPERIPH_DRIVER -I../src -I..\Libraries\CMSIS\Include -I..\Libraries\CMSIS\Device\ST\STM32F30x\Include -I..\Libraries\STM32F30x_StdPeriph_Driver\inc -I''C:\cvs_projects\Roboteq FOC\Firmware\Brushless_FOC\FreeRTOS 7.5.2\inc'' -I''C:\cvs_projects\Roboteq FOC\Firmware\Brushless_FOC\inc'' -I''C:\cvs_projects\Roboteq FOC\Firmware\Brushless_FOC\Drivers\inc'' -O3 -ffunction-sections -fdata-sections -g -Wall
Anyone know if there indeed something wrong, and if so, how to fix it?
Thanks,
Alex
