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Basically, the HAL driver APIs are called from user files and optionally from interrupt handlers file when the APIs based on the DMA or the PPP peripheral dedicated interrupts are used.
When DMA or PPP peripheral interrupts are used, the PPP process complete callbacks are called to inform the user about the process completion in real-time event mode (interrupts).
Note that the same process completion callbacks are used for DMA in interrupt mode.
2.12.2 HAL initialization
2.12.2.1 HAL global initialization
In addition to the peripheral initialization and de-initialization functions, a set of APIs are provided to initialize the HAL core implemented in file stm32f4xx_hal.c.
HAL_Init(): this function must be called at application startup to
Initialize data/instruction cache and pre-fetch queue
Set Systick timer to generate an interrupt each 1ms (based on HSI clock) with the lowest priority
Set priority grouping to 4 preemption bits
Call HAL_MspInit() user callback function to perform system level initializations
(Clock, GPIOs, DMA, interrupts). HAL_MspInit() is defined as “weak” empty function in the HAL drivers.
HAL_DeInit()
Resets all peripherals
Calls function HAL_MspDeInit() which is a user callback function to do system level De-Initalizations.
HAL_GetTick(): this function gets current SysTick counter value (incremented in
SysTick interrupt) used by peripherals drivers to handle timeouts.
HAL_Delay(). this function implements a delay (expressed in milliseconds) using the
SysTick timer.
Care must be taken when using HAL_Delay() since this function provides an accurate delay (expressed in milliseconds) based on a variable incremented in SysTick ISR.
This means that if HAL_Delay() is called from a peripheral ISR, then the SysTick interrupt must have highest priority (numerically lower) than the peripheral interrupt, otherwise the caller ISR will be blocked.
In STM32Cube V1.0 implemented in STM32CubeF2 and STM32CubeF4 first versions, the SysTick timer is used as default timebase. This has been modified to allow implementing user-defined timebases (such as a general-purpose timer), keeping in mind that the timebase duration must be kept at 1 ms since all
PPP_TIMEOUT_VALUEs are defined and handled in milliseconds. This enhancement is implemented in STM32Cube V1.1 that is deployed starting from
STM32CubeL0/F0/F3 and later. This modification is backward compatible with
STM32Cube V1.0 implementation. Functions affecting timebase configurations are declared as __Weak to allow different implementations in the user file.
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2.12.2.2 System clock initialization
The clock configuration is done at the beginning of the user code. However the user can change the configuration of the clock in his own code. Please find below the typical Clock configuration sequence: static void SystemClock_Config(void)
{
RCC_ClkInitTypeDef RCC_ClkInitStruct;
RCC_OscInitTypeDef RCC_OscInitStruct;
/* Enable HSE Oscillator and activate PLL with HSE as source */
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
RCC_OscInitStruct.PLL.PLLM = 25;
RCC_OscInitStruct.PLL.PLLN = 336;
RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
RCC_OscInitStruct.PLL.PLLQ = 7;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
/* Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2 clocks dividers */
RCC_ClkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK |
RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2);
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;
HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5); }
2.12.2.3 HAL MSP initialization process
The peripheral initialization is done through HAL_PPP_Init() while the hardware resources initialization used by a peripheral (PPP) is performed during this initialization by calling
MSP callback function HAL_PPP_MspInit().
The MspInit callback performs the low level initialization related to the different additional hardware resources: RCC, GPIO, NVIC and DMA.
All the HAL drivers with handles include two MSP callbacks for initialization and deinitialization:
/**
* @brief Initializes the PPP MSP.
* @param hppp: PPP handle
* @retval None */ void __weak HAL_PPP_MspInit(PPP_HandleTypeDef *hppp) {
/* NOTE : This function Should not be modified, when the callback is needed, the HAL_PPP_MspInit could be implemented in the user file */
}
/**
* @brief DeInitializes PPP MSP.
* @param hppp: PPP handle
* @retval None */ void __weak HAL_PPP_MspDeInit(PPP_HandleTypeDef *hppp) {
/* NOTE : This function Should not be modified, when the callback is needed, the HAL_PPP_MspDeInit could be implemented in the user file */
}
The MSP callbacks are declared empty as weak functions in each peripheral driver. The user can use them to set the low level initialization code or omit them and use his own initialization routine.
The HAL MSP callback is implemented inside the stm32f4xx_hal_msp.c file in the user folders. An stm32f4xx_hal_msp.c file template is located in the HAL folder and should be copied to the user folder. It can be generated automatically by STM32CubeMX tool and
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