Firmware Lib problem calc BRR register for usart

[christoph239955_stm1_st]

Posted on August 26, 2009 at 12:24

Firmware Lib problem calc BRR register for usart

[varun]

Posted on May 17, 2011 at 13:21

Hi Christoph,

How did you found that your resulting baud is not correct? I mean are you using some debugger or simulator to do that?

First ensure that you have modified the oscillator specification as per your hardware

#define HSE_Value ((u32)8000000) /* change here in stm32f10x_conf.h */

In case you are using keil simulator, ensure that Xtal specification in Target option is same as HSE_Value.

Also, the keil simulator some time misbehaves for the peripheral clock values shown in dialog box. To ensure this doesn't happen, first open,

peripherals -> power, reset and clock control window..... close it then open the respective peripheral windows!! :-]

Regards,

Varun

[christoph239955_stm1_st]

Posted on May 17, 2011 at 13:21

Hello,

hopefully anyone can help me. I use the STM32F107VCT6 on the STM3210c-Eval board.

is it possible that the library function ''USART_Init'' works not correct?

I setup the USART 2 and use the lib-function and the Usart-init struct.

when I try to get the USART2 work with 9600 baud with the lib-function it doesn’t work.

But if I calculate the BRR Register values ''by hand'' it works fine!

I tried to get the system clocks with the lib-function ''RCC_GetClocksFreq'' but this function gives strange frequencies!

so maybe this function works not correct?

here the usart configuration:

-----------------------------

void SetUSART(){

/* The following example illustrates how to configure the USART1 */

/* Resets the USART1 registers to their default reset value */

RCC_ClocksTypeDef RCC_ClocksStatus; // for test

USART_DeInit(USART2);

USART_Cmd(USART2, ENABLE); // Enable USART 2

USART_InitStructure.USART_BaudRate = 9600;

USART_InitStructure.USART_WordLength = USART_WordLength_8b;

USART_InitStructure.USART_StopBits = USART_StopBits_1;

USART_InitStructure.USART_Parity = USART_Parity_No;

USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;

USART_InitStructure.USART_Mode = USART_Mode_Tx | USART_Mode_Rx;

RCC_GetClocksFreq(&RCC_ClocksStatus); //for test

USART_Init(USART2, &USART_InitStructure); // init USART 2 with init structure

USART_ITConfig(USART2, USART_IT_RXNE , ENABLE); // Enables the USART2 Receive interrupt

USART_ITConfig(USART2, USART_IT_TXE, ENABLE); // Enables the USART2 Transmission Complete interrupt

/* Write to USART BRR */

USART2->BRR = 0x146; //20,36d

}

here the clock configuration:

-----------------------------

void SetCLK(){

ErrorStatus HSEStartUpStatus;

// RCC = Reset Clock Control

/* RCC system reset(for debug purpose) */

RCC_DeInit();

/* Enable HSE (>High speed external clock here: 25Mhz)*/

RCC_HSEConfig(RCC_HSE_ON); // switch to external oscillator

/* Disable Internal High Speed oscillator */

RCC_HSICmd(DISABLE);

/* Wait till HSE is ready */

HSEStartUpStatus = RCC_WaitForHSEStartUp(); // check stable clock source

if(HSEStartUpStatus == SUCCESS){

/* HCLK = SYSCLK */

RCC_HCLKConfig(RCC_SYSCLK_Div1); // System Clock

/* PCLK2 = HCLK */

RCC_PCLK2Config(RCC_HCLK_Div1); // peripheral clock 2

/* PCLK1 = HCLK/2 */

RCC_PCLK1Config(RCC_HCLK_Div2); // peripheral clock 1

/* Flash 2 wait state */

FLASH_SetLatency(FLASH_Latency_2);

/* Enable Prefetch Buffer */

FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);

/* PLLCLK = 25MHz * 2 = 50 MHz */

RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_2); // PLL clock

/* Enable PLL */

RCC_PLLCmd(ENABLE); // enable the pll clock

/* Wait till PLL is ready */

while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET){} // wait until PLL is ready

/* Select PLL as system clock source */

RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);// system clock = PLLCLOCK

/* Wait till PLL is used as system clock source */

while(RCC_GetSYSCLKSource() != 0x08){} // wait for ready clock

/* Configure HCLK such as HCLK = SYSCLK (AHB prescaler)*/

RCC_HCLKConfig(RCC_SYSCLK_Div1);

/* Configure PCLK1 such as PCLK1 = HCLK/16 (APB1 Prescaler)*/

// PCLK1 for: TIM2 and USART2

RCC_PCLK1Config(RCC_HCLK_Div16);

}

/* Enable GPIO and USART1 clock */

RCC_APB2PeriphClockCmd(RCC_APB2Periph_ALL, ENABLE);

/* Enable Timer2..7 clock */

RCC_APB1PeriphClockCmd(RCC_APB1Periph_ALL, ENABLE);

}

thanks for any helpnullhere the clock configuration:

[christoph239955_stm1_st]

Posted on May 17, 2011 at 13:21

thanks Varun,

I use the Ride7 with the Rlink to debug the Evalboard.

I can see the clock frequencies in the watchwindow.

Thanks for the tip in the *conf.h i forgot... ;)

Now the frequencies are correct.

I added the sourcecode files *usart.c and *rcc.c and all

works fine. :D

thanks for your help