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Linearity of HRTim Compare

pv_he
Associate

Hello together,

when inspecting the behaviour of the HRTimer regarding the compare output, I found that with Clk multiplier 32, there is a non-linearity in the compare timing (stepwidth) of about +150 ps (330 ps step instead of 180 ps between adjacent compare values). This seems directly to correlate with the depth of the delay line, as I can see this step equally distributed each 32 steps.

Is this known or is there a way to avoid this behaviour and get a more linear behaviour?

My test setup is:

STM32G474, HRTim1

Channel B: 1 MHz pulses, continious

Channel C: single shot, resettable, triggered by Chan B, variable compare value. Set on compare, reset on period.

I checked the delay of the output C regarding to B. Basically I get quite good results with a standard deviation of appr. 30 ps but I wonder of this non-linear step. The step e.g. happens when changing the compare value from 183 to 184 (or 215 to 216).

Br,

Pascal

2 REPLIES 2
Hz Lin
Associate II

I have similar concerns. Any update on this?

MasterT
Senior III

Does this function make any difference:

if (HAL_HRTIM_DLLCalibrationStart(&hhrtim1, HRTIM_CALIBRATIONRATE_3) != HAL_OK) ?

FYI, HAL driver internal info:

#define HRTIM_SINGLE_CALIBRATION    0xFFFFFFFFU                                    /*!< Non periodic DLL calibration */
#define HRTIM_CALIBRATIONRATE_0     0x00000000U                                    /*!< Periodic DLL calibration: T = 1048576U * tHRTIM (6.168 ms) */
#define HRTIM_CALIBRATIONRATE_1     (HRTIM_DLLCR_CALRTE_0)                         /*!< Periodic DLL calibration: T = 131072U * tHRTIM (0.771 ms) */
#define HRTIM_CALIBRATIONRATE_2     (HRTIM_DLLCR_CALRTE_1)                         /*!< Periodic DLL calibration: T = 16384U * tHRTIM (0.096 ms) */
#define HRTIM_CALIBRATIONRATE_3     (HRTIM_DLLCR_CALRTE_1 | HRTIM_DLLCR_CALRTE_0)  /*!< Periodic DLL calibration: T = 2048U * tHRTIM (0.012 ms) */