DocID026506 Rev 1

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AN4539

Getting the kitchen ready

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1.

Selection of the high-speed PLL output for the HRTIM in RCC_CFGR3 register:

__HAL_RCC_HRTIM1_CONFIG(RCC_HRTIM1CLK_PLLCLK);

2.

Clock enable for the registers mapped on the APB2 bus.

__HRTIM1_CLK_ENABLE();

1.4.3

HRTIM DLL initialization

The HRTIM’s Delay-Locked Loop (DLL) is responsible for providing fine-grained timings and

divide the high-frequency (144 or 128MHz) clock period into 32 evenly spaced steps.

This DLL must be calibrated at least once before high-resolution can be used. The

calibration can be transparently re-launched by software during HRTIM operation if voltage

or temperature conditions have changed. It is also possible to enable periodic calibration by

hardware.

The code snippet below shows how the calibration is done. The high-resolution can be used

once the DLLRDY flag has been set.

/* DLL calibration: periodic calibration enabled, period set to 14µs */

HRTIM1->sCommonRegs.DLLCR = HRTIM_CALIBRATIONRATE_14| HRTIM_DLLCR_CALEN;

/* Check DLL end of calibration flag */

while(HRTIM1->sCommonRegs.ISR & HRTIM_IT_DLLRDY == RESET);

It is recommended to have the periodic calibration enabled, with the lowest calibration

period (set at 14µs), as default condition.

Note:

The code here below will cause the execution to stall if the DLL does not lock (typically if the

HSE oscillator is not properly configured). The HAL library includes a function to perform the

calibration which has a timeout verification and redirect in an error handler if necessary. This

function is the one used in the HAL-based software example.

1.4.4

HRTIM I/Os initialization

The HRTIM inputs and outputs are mapped on standard I/O ports and have to be

programmed as any other I/O peripheral. The HRTIM alternate functions are split between:

•

AF13 channel (for HRTIM I/O ports located on ports A and B);

•

AF3 channel (for HRTIM I/O ports located on port C)

The HRTIM I/Os initialization must be done in two phases. The HRTIM inputs are initialized

first, prior to the HRTIM registers, in the HAL_HRTIM_MspInit function.

The HRTIM outputs must be initialized after the HRTIM control registers programming (done

in the GPIO_HRTIM_outputs_Config function in the examples), and once the counters are

enabled. This is to ensure that the outputs states are correctly defined inside the HRTIM

before passing the control from the GPIO circuitry to the HRTIM timer.

1.4.5

Other peripherals initialization

The HRTIM interacts with many of the MCU peripherals, as listed below. It is not mandatory

to have all of them initialized to have the HRTIM operating. Initialization codes for the

peripherals below are available in some of the examples described later.