STM32F103:Problem with USART when use System Tick Timer Delay in us

[dark_killer_1796]

Posted on February 28, 2015 at 03:34

Hi all,

I am using STM32F103RCT6 and CP2102 as UART controller driver.I have problem with USART when I use SysTick Timer to generate 1us Delay.The problem is that when I configure SysTick at frequency 1Mhz, the program does not work.SysTick_Config(SystemCoreClock / 1000000)   // SystemCoreClock is 72 MhzI use SysTick to generate 1us Delay: void Delay(__IO uint32_t nTime){  TimingDelay = nTime;        // Timing Delay is a volatile uint32_t variable while(TimingDelay != 0);}void TimingDelay_Decrement(void){ if (TimingDelay != 0x00) {  TimingDelay--; }}SysTick handlervoid SysTick_Handler(void){ TimingDelay_Decrement(); Tick++;     // my private variable for counting     }That is how I create my Delay function in microsecond.It works well, but when I want to add USART code, the program doesn't work. When I call USART_Configuration(); in main, the program stucks.void USART_Configuration(void){ USART_InitTypeDef USART_InitStructure; RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);  /* Configure PA9 for USART Tx as alternate function push-pull */ GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init(GPIOA, &GPIO_InitStructure); /* Configure PA10 for USART Rx as input floating */ GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING; GPIO_Init(GPIOA, &GPIO_InitStructure); /* USARTx configured as follow:        - BaudRate = 115200 baud          - Word Length = 8 Bits        - One Stop Bit        - No parity        - Hardware flow control disabled (RTS and CTS signals)        - Receive and transmit enabled  */ USART_InitStructure.USART_BaudRate = 115200; 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_Rx | USART_Mode_Tx; /* USART configuration */ USART_Init(USART1, &USART_InitStructure); /* Enable USART */ USART_Cmd(USART1, ENABLE); }I tried to configure SysTick at 100Khz (delay with resolution 10us), it worked.SysTick_Config(SystemCoreClock / 100000);But my application needs a delay at us. I don't know what is the reason and how to solve it. Can anyone give me some advice. Thank you for reading. #it''s-deja-vu-all-over-again

[Tesla DeLorean]

Posted on February 28, 2015 at 04:43

Interrupting at 1 MHz is insane, 72 machine cycles, 22 cycles for an interrupt doing nothing, perhaps 3 cycles per FLASH read. You really need to ponder how the machine works.

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[childresss]

Posted on February 28, 2015 at 07:03 delayMicroseconds() with a 1mSec systick - is done by reading the systick timer and calculating how many microseconds (from counter's clock freq) since the last 1mSec counter match where the timer was reset. No silly loops.

[Tesla DeLorean]

Posted on February 28, 2015 at 16:24

But the granularity is a little courser, and the math is more awkward.. Not sure that's a win