Objective
In this tutorial we will discuss how to configure lpc1768 systick timer for 1ms tick.
At the end of the tutorial we will see how to use the ExploreEmbedded sysTick libraries.
Systick Module
The System Tick Timer is an integral part of the Cortex-M3. The System Tick Timer is intended to generate a fixed 10 millisecond(user configurable) interrupt for use by an operating system or other system management software.
The System Tick Timer is a 24-bit timer that counts down to zero and generates an interrupt. The intent is to provide a fixed time interval between interrupts.
In order to generate recurring interrupts at a specific interval, the STRELOAD register must be initialized with the correct value for the desired interval.
Registers
| Register | Address | Description |
|---|---|---|
| STCTRL | 0xE000 E010 | System Timer Control and status register |
| STRELOAD | 0xE000 E014 | System Timer Reload value register |
| STCURR | 0xE000 E018 | System Timer Current value register |
| STCALIB | 0xE000 E01C | System Timer Calibration value register |
| STCTRL | |||||
| 31-17 | 16 | 15-3 | 2 | 1 | 0 |
| RESERVED | COUNTFLAG | RESERVED | CLKSOURCE | TICKINT | ENABLE |
Bit 15:4 - RESULT
This field contains the 12bit A/D conversion value for the selected channel in ADCR.SEL
The vale for this register should be read oncve the conversion is completed ie DONE bit is set.
Bit 26:24 - CHN : Channel
These bits contain the channel number for which the A/D conversion is done and the converted value is available in RESULT bits(e.g. 000 identifies channel 0, 011 channel 3...).
Bit 27 - OVERRUN
This bit is set during the BURST mode where the previous conversion data is overwritten by the new A/D conversion value.
Bit 31 - DONE
This bit is set to 1 when an A/D conversion completes. It is cleared when this register is read and when the ADCR is written. If the ADCR is written while a conversion is still in progress, this bit is set and a new conversion is started.
Code
Using ExploreEmbedded Libraries
