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38.6 Example configuration for chained timers
In the example configuration:
• The PIT clock has a frequency of 100 MHz.
• Timers 1 and 2 are available.
• An interrupt shall be raised every 1 hour.
The PIT module needs to be activated by writing a 0 to MCR[MDIS].
The 100 MHz clock frequency equates to a clock period of 10 ns, so the PIT needs to
count for 6000 million cycles, which is more than a single timer can do. So, Timer 1 is
set up to trigger every 6 s (600 million cycles). Timer 2 is chained to Timer 1 and
programmed to trigger 10 times.
The value for the LDVAL register trigger is calculated as number of cycles-1, so
LDVAL1 receives the value 0x23C345FF and LDVAL2 receives the value 0x00000009.
The interrupt for Timer 2 is enabled by setting TCTRL2[TIE], the Chain mode is
activated by setting TCTRL2[CHN], and the timer is started by writing a 1 to
TCTRL2[TEN]. TCTRL1[TEN] needs to be set, and TCTRL1[CHN] and TCTRL1[TIE]
are cleared.
The following example code matches the described setup:
// turn on PIT
PIT_MCR = 0x00;
// Timer 2
PIT_LDVAL2 = 0x00000009; // setup Timer 2 for 10 counts
PIT_TCTRL2 = TIE; // enable Timer 2 interrupt
PIT_TCTRL2 |= CHN; // chain Timer 2 to Timer 1
PIT_TCTRL2 |= TEN; // start Timer 2
// Timer 1
PIT_LDVAL1 = 0x23C345FF; // setup Timer 1 for 600 000 000 cycles
PIT_TCTRL1 = TEN; // start Timer 1
Example configuration for chained timers
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
974
Preliminary
Freescale Semiconductor, Inc.
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