ST官方提供的STM8S固件库不是有这个示例吗？
STM8S上电复位默认就是使用HSI在工作的，8分频，频率是2MHz。不用在切了，直接该分频比即可。
下面是ST提供的一个直接对寄存器操作的例子，实现HSE和HSI切换:
This example provides two optimal clock configurations and switching between
them. After reset the application is running on HSI with fcpu 16Mhz. When the
KEY button is pressed switch to 24Mhz HSE in manual mode is performed. Fcpu
could be controled on MCO pin (PE0) by scope. Change of All LEDs blinking
frequency could be observed by eye.
******************************************************************************
* @file CLK_example1\main.c
* @brief This file contains the main function for CLK example 1.
* @author STMicroelectronics, MCD Application Team
* @version 1.02
* @date 1-JUN-2009
******************************************************************************
*
* THE PRESENT SOFTWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS
* WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE
* TIME. AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY
* DIRECT, INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING
* FROM THE CONTENT OF SUCH SOFTWARE AND/OR THE USE MADE BY CUSTOMERS OF THE
* CODING INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.
*
* <h2><center>© COPYRIGHT 2009 STMicroelectronics</center></h2>
* @image html **.bmp
******************************************************************************
*/
/* Includes ------------------------------------------------------------------*/
#include "stm8s.h"
/**
* @addtogroup CLK_Example1
* @{
*/
/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
#define to_HSE 0xB4 // definition of clock blocks (to be copied to SWR)
#define to_LSI 0xD2
#define to_HSI 0xE1
#define ALL_LEDs ((u8)0x0F) // LEDs mask (EVAL board)
#define BUTTON ((u8)0x01) // Button mask (EVAL board)
#define CLK_SWITCH_TIMEOUT ((u16)0x491) //timeout for clock switching
/* Private macro -------------------------------------------------------------*/
#define switch_all_LEDs_on { GPIOH->ODR|= ALL_LEDs; } //LEDs control
#define switch_all_LEDs_off { GPIOH->ODR&=~ALL_LEDs; }
#define button_is_pressed ((GPIOC->IDR & BUTTON) == 0)
/* Private variables ---------------------------------------------------------*/
/* Private function prototypes -----------------------------------------------*/
/**
* @brief Programable loop delay
* @par Parameters:
* nCnt: multiply factor of the number of loops
* @retval None
*/
void Delay(u8 nCnt) {
u32 nCount= nCnt*(u32)10000;
while (nCount != 0) {
nCount--;
}
}
/* -------------------------------------------------------------------------- */
/**
* @brief Switch to selected clock using manual mode.
* @par Parameters:
* clck: to_HSE, to_LSI, to_HSI - block to switch
* @retval TRUE in case of succes else FALSE
*/
u8 switch_clock_system(u8 clck) {
u16 Tout= CLK_SWITCH_TIMEOUT;
CLK->SWCR &= ~CLK_SWCR_SWIF; // manual switch mode
CLK->SWR= clck;
while ( !(CLK->SWCR & CLK_SWCR_SWIF) && Tout)
Tout--; // wait for targed block is ready
if(Tout) {
CLK->SWCR|= CLK_SWCR_SWEN; // new block is ready - make switch!
return(TRUE); // return SUCCES!
}
else {
CLK->SWCR &= ~CLK_SWCR_SWBSY; // reswitch to original clock source
return(FALSE); // return switching wasn't succesfull
}
}
/* Public functions ----------------------------------------------------------*/
/**
* @brief Validation firmware main entry point.
* @par Parameters:
* None
* @retval void None
*/
void main(void) {
u8 succ;
u8 butt;
// *** GIO INIT ***
GPIOH->ODR &=~ALL_LEDs; // LEDs - as push-pull outputs, all off
GPIOH->DDR |= ALL_LEDs;
GPIOH->CR1 |= ALL_LEDs;
GPIOC->CR1 |= BUTTON; // BUTTON input settings: Input pull-up
GPIOC->DDR &=~BUTTON;
// *** CLK INIT ***
CLK->CKDIVR &= (u8)~(CLK_CKDIVR_CPUDIV); // fcpu= fmaster (CPUDIV= 0)
CLK->CKDIVR &= (u8)~(CLK_CKDIVR_HSIDIV); // fhsi= fhsirc (HSIDIV= 0)
CLK->CCOR |= (u8)((4<<1) & CLK_CCOR_CCOSEL);// fcpu -> CCO pin
CLK->CCOR |= (u8)(CLK_CCOR_CCOEN);
butt= FALSE;
// *** MAIN LOOP ***
while(1) {
if(button_is_pressed && butt == FALSE)
{// test one time switch condition
succ= switch_clock_system(to_HSE); // switch from HSI to HSE clock
butt= TRUE;
}
switch_all_LEDs_on; // switch on all LEDs
Delay(1); // delay
switch_all_LEDs_off; // LEDs off
Delay(1); // delay
};
}
/**
* @}
*/
/******************* (C) COPYRIGHT 2009 STMicroelectronics *****END OF FILE****/
验证例程需要注意的事项：
1、例程使用硬件为ST官方的STM8S-128/Eval，基于STM8S208
2、At least 1 wait state for reading flash and data memory should be performed
if cpu works at 24Mhz fcpu frequency - set corresponding option register
e.g. in STVD via MCU configuration window:
(Debug instrument -> MCU configuration -> Option -> WAITSTATE -> 1)
总的一句话208要运行在24MHz，需要在optionbytes配置一个时钟等待周期。你跑16MHz不要理会这句话。
3、the switching routine can be used for LSI initialization if it is called
with parameter to_LSI (LSI_EN bit should be set in that case in corresponding
option EEPROM register via MCU configuration window: ...option -> LSI_EN -> Enabled)
例程会可能使用到LSI，请打开Optionbytes中的LSI_EN位。 |
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