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4 STM32's SysTick.ppt
- 1. STM32 Systick Md Rayhan Tanvir
- 2. Directory SysTick Introduction 1 SysTick Function description 2 SysTick Basic operations 3
- 4. SysTick Introduction The System Tick Timer (SysTick) generates interrupt requests on a regular basis. This allows an OS to carry out context switching to support multiple tasking.
- 5. SysTick Introduction ARM Cortex-M3 Timer On-Chip peripherals JTAG SWD CPU SysTick NVIC Chips from different manufacturers NVIC ARM Cortex-M3 Kernel Nested Vector Interrupt Controller SysTick is a 24-bit system clock counter, down counting mode, it belongs to ARM Cortex-M3 kernel NVIC in a functional unit, often used for operating system clock timing. Without operating system, the Systick can be used as a general timer/counter
- 6. JTAG & SWD Serial Wire Debug (SWD) is a 2-pin (SWDIO/SWCLK) electrical alternative JTAG interface that has the same JTAG protocol on top. SWD uses an ARM CPU standard bi-directional wire protocol. Joint Test Action Group (JTAG) is an electronics industry association formed in 1985 for developing a method of verifying designs and testing printed circuit boards after manufacture.
- 7. NVIC (Nested Vector Interrupt Controller) Asynchronous interrupts don’t wait for previous ones to be handled - if you’re handling the last one when a new one comes along, you either ignore it or you have a CPU that can nest them and handle it when you finish the current one (or preserve the current state and handle the new one - it depends on priority).
- 8. Downcounting
- 9. TI Cortex-M3 NXP Cortex-M3 TI Cortex-M3 SysTick Introduction Operating system code porting Using Timers as System Clock Can't be Carried directly. Can be carried directly µC/OS-II Operating NXP Cortex-M3 µC/OS-II Operating Use SysTick as System Clock
- 10. SysTick Introduction Systick timers can be used for other purposes in addition to operating systems: as a alarm, for measuring time. Note that when the processor is called to stop during debugging (Halt), the Systick timer will also be suspended.
- 11. Directory SysTick Introduction 1 SysTick Function description 2 SysTick Basic operations 3
- 12. SysTick Registers SysTick can be configured through the 4 registers:
- 13. SysTick Structure Diagram FLAG RELOAD CURRENT 0 ENABLE TICKINT CLKSOURCE 0 1 Reload value register Current Value Registers Control and Status registers Clock Interrupt
- 14. Register description SysTick Control and Status registers (SysTick_CSR) COUNTFLAG CLKSOURCE TICKINT ENABLE bit0 bit1 bit2 bit16 Counter flag bit 0: Read zeroing 1: The counting value is reduced from 1 to 0 Clock source Selection bit 0: External reference clock-HCLK/8 1: Kernel clock-HCLK 0: No interruption 1: Allow interrupt Interrupt Enable bit Counter enables bit 0: Prohibition 1: Enable Count values from 1 to 0 triggers an Interrupt. The bit will automatically clear 0 after reading; can be used for query mode timing
- 15. SysTick Clock source SysTick's clock source can be HCLK/8 or HCLK specifically which can be selected by configuring control and status registers (CTRL).
- 16. 0 Current Value Registers (SysTick_VAL) Register description The current value register displays the current value of the SysTick counter. Every 1 system clock cycles, the value minus 1, when the count is reduced to 0, can produce interrupts and load the values of the reload value registers. 0x000003 Count Flag bit COUNTFLAG Interrupt Current Value Registers Reload Value Registers 0x000003 0x000002 0x000001 0x000000 0x000003 0x000003 1 0x000000 Any value Write any value to zero and cause the sign to be zeroed.
- 17. Directory SysTick Introduction 1 SysTick Function description 2 SysTick Basic operations 3
- 18. SysTick How to Run Select Clock Source Set Reload values Enable SysTick interruption Enable SysTick counter CTRL—>CLKSOURCE When the count value is reduced from 1 to 0, the interrupt is generated Start Counter & Start Countdown RELOAD=(SysClock * Timing time) -1 Empty Current Value Registers Automatically load reload values when the count is 0
- 19. SysTick How to Run CURRENT FLAG 0x000003 RELOAD 0x000000 0 ENABLE TICKINT CLKSOURCE 0 1 Clock Interrupt Select Kernel Clock 1 Set Reload values 2 Enable interruption 3 Enable counter 4 0x000003 0x000002 0x000000 0x000001 1 Interrupt 1 1