AN3427 datasheet(39/52 Pages) STMICROELECTRONICS

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AN3427

Firmware migration using the library

Doc ID 019001 Rev 1

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used to configure the microcontroller system at start-up and before branching to the

main() program.

Note:

For STM32F2xx you can use the clock configuration tool,

STM32F2xx_Clock_Configuration.xls, to generate a customized SystemInit() function

depending on your application requirements. For more information, refer to the application

note AN3362 “Clock configuration tool for STM32F2xx microcontrollers”

Peripheral access configuration: as presented in Section 3.4: RCC you need to call

different functions to [enable/disable] or [enter/exit] the peripheral [clock] or [from reset

mode]. For example, GPIOA is mapped on AHB1 bus on F2 series (APB2 bus on F1

series), to enable its clock you have to use the

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

function instead of:

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

in the F1 series. Refer to Table3 on page13 for the peripheral bus mapping changes

between F2 and F1 series.

Peripheral clock configuration

I2S: in STM32 F2 series the I2S clock can be derived either from a specific PLL

(PLLI2S) or from an external clock mapped on the I2S_CKIN pin. Refer to the

code given below, that should be used in both cases:

/******************************************************************************/

PLLI2S used as I2S clock source

/******************************************************************************/

/* Select PLLI2S as I2S clock source */

RCC_I2SCLKConfig(RCC_I2S2CLKSource_PLLI2S);

/* Configure the PLLI2S clock multiplication and division factors

Note: PLLI2S clock source is common with the main PLL (configured in

RCC_PLLConfig function )

RCC_PLLI2SConfig(PLLI2SN, PLLI2SR);

/* Enable PLLI2S */

RCC_PLLI2SCmd(ENABLE);

/* Wait till PLLI2S is ready */

while(RCC_GetFlagStatus(RCC_FLAG_PLLI2SRDY) == 0)

{

}

/* Enable I2Sx’s APB interface clock (I2S2/3 are subset of SPI2/3 peripherals) */

RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPIx, ENABLE);

/******************************************************************************/

External clock used as I2S clock source

/******************************************************************************/

/* Select External clock mapped on the I2S_CKIN pin as I2S clock source */

RCC_I2SCLKConfig(RCC_I2S2CLKSource_Ext);

/* Enable I2Sx’s APB interface clock (I2S2/3 are subset of SPI2/3 peripherals) */

RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPIx, ENABLE);

USB OTG FS and SDIO: in STM32 F2 series the USB OTG FS requires a

frequency of 48 MHz to work correctly, while the SDIO requires a frequency of less

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