Peter Drescher / ST_L152_32MHZ

Lib to change the clock speed of the ST Nucleo L152RE board to 32 MHz.

The ST Nucleo L152 board is running on 16 MHz out of the box. To speed up the cpu to the maximum 32MHz speed we have to change the clock setting. Simply add the lib and : 

         #include "ST_L152_32MHZ.h"
        L152_init32 myinit(0);   // use the internal oscillator

in front of your program. This should be the first line in main to ensure the frequency is changed before other objects are initialised.

This frequency is generated out of the internal RC oscillator. The frequency is not so stable like a crystal. The PLL is switched to 96MHz to enable the use of the USB interface.

If you need a more precise timing source, you have to add a external crystal.

/media/uploads/dreschpe/oszillator.jpg

You need : X3 8MHz crystal , C33 and C34 18pF 0603 , R35 and R37 have to be short with a small piece of wire.

         #include "ST_L152_32MHZ.h"
        L152_init32 myinit(1);   // use external crystal oscillator

ST_L152_32MHZ.cpp@0:84e23a19e37d, 2014-03-11 (annotated)

Committer:
dreschpe
Date:
Tue Mar 11 20:34:57 2014 +0000
Revision:
0:84e23a19e37d
Child:
1:bdeac50afe1a
Lib for the ST Nucleo L152RE board to switch the clock to 32MHz.; Out of the box the board is running on 16MHz.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
dreschpe 0:84e23a19e37d 1
dreschpe 0:84e23a19e37d 2
dreschpe 0:84e23a19e37d 3 #include "stm32l1xx.h"
dreschpe 0:84e23a19e37d 4 #include "stm32l1xx_flash.h"
dreschpe 0:84e23a19e37d 5 #include "stm32l1xx_rcc.h"
dreschpe 0:84e23a19e37d 6 #include "ST_L152_32MHZ.h"
dreschpe 0:84e23a19e37d 7
dreschpe 0:84e23a19e37d 8 // set cpu clock to 32MHz
dreschpe 0:84e23a19e37d 9
dreschpe 0:84e23a19e37d 10
dreschpe 0:84e23a19e37d 11
dreschpe 0:84e23a19e37d 12 L152_init32::L152_init32(unsigned int external){
dreschpe 0:84e23a19e37d 13 clk_err = setup_clock_32MHZ(external);
dreschpe 0:84e23a19e37d 14 }
dreschpe 0:84e23a19e37d 15
dreschpe 0:84e23a19e37d 16 #define PLL_STARTUP_TIMEOUT 0x5000
dreschpe 0:84e23a19e37d 17
dreschpe 0:84e23a19e37d 18 int L152_init32::setup_clock_32MHZ(int external)
dreschpe 0:84e23a19e37d 19 {
dreschpe 0:84e23a19e37d 20 uint32_t PLLStartUpCounter = 0,PLLStatus = 0,error;
dreschpe 0:84e23a19e37d 21
dreschpe 0:84e23a19e37d 22 if(external == 0) { // internal Oscillator
dreschpe 0:84e23a19e37d 23 RCC_PLLConfig(RCC_PLLSource_HSI,RCC_PLLMul_6,RCC_PLLDiv_3); // setup pll to 96MHz to use USB
dreschpe 0:84e23a19e37d 24 } else {
dreschpe 0:84e23a19e37d 25 RCC_HSEConfig(RCC_HSE_ON); // start external crystal osc.
dreschpe 0:84e23a19e37d 26 error = RCC_WaitForHSEStartUp();
dreschpe 0:84e23a19e37d 27 if(error == ERROR ) { // no external crystal
dreschpe 0:84e23a19e37d 28 return(0);
dreschpe 0:84e23a19e37d 29 }
dreschpe 0:84e23a19e37d 30 RCC_PLLConfig(RCC_PLLSource_HSE,RCC_PLLMul_12,RCC_PLLDiv_3); // setup pll to 96MHz to use USB
dreschpe 0:84e23a19e37d 31 }
dreschpe 0:84e23a19e37d 32 RCC_PLLCmd(ENABLE); // switch on pll
dreschpe 0:84e23a19e37d 33 do {
dreschpe 0:84e23a19e37d 34 PLLStatus = RCC->CR & RCC_CR_PLLRDY;
dreschpe 0:84e23a19e37d 35 } while((PLLStatus == 0) && (PLLStartUpCounter < PLL_STARTUP_TIMEOUT)); // wait for pll
dreschpe 0:84e23a19e37d 36 if(PLLStatus == 0) {
dreschpe 0:84e23a19e37d 37 return(0);
dreschpe 0:84e23a19e37d 38 }
dreschpe 0:84e23a19e37d 39 FLASH_SetLatency(FLASH_Latency_1);
dreschpe 0:84e23a19e37d 40 FLASH_PrefetchBufferCmd(ENABLE);
dreschpe 0:84e23a19e37d 41 FLASH_ReadAccess64Cmd(ENABLE);
dreschpe 0:84e23a19e37d 42 RCC_HCLKConfig(RCC_SYSCLK_Div2);
dreschpe 0:84e23a19e37d 43 RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK); // switch to 32 MHz clock
dreschpe 0:84e23a19e37d 44 SystemCoreClockUpdate(); // update SystemCoreClock var
dreschpe 0:84e23a19e37d 45 return(1);
dreschpe 0:84e23a19e37d 46 }