Forum Discussion
Honored ContributorTimer Period not correctly
Hi all,
my goal is to set a timer with a period time of 1ms and start it. After the time is elapsed it should rise an IRQ (once). The timer itself with interrupt works, but the time is always about 6 to 8us. regardless what i write into the timer period registers? I also tried to set 80'000 (80MHz clock) but nothing changed on the 6 to 8 us. qsys settings: Period: 1us size: 32bit Hardware Options: Full featured Here the code for the timer: init:
alt_ic_isr_register(HIRES_TIMER_IRQ_INTERRUPT_CONTROLLER_ID, HIRES_TIMER_IRQ, hires_timer_ISR, NULL, NULL);
void hires_timer_ISR() {
IOWR_ALTERA_AVALON_PIO_DATA(DEBUG_BASE, 0);
IOWR_ALTERA_AVALON_TIMER_CONTROL(HIRES_TIMER_BASE, 0x0000); // disable IRQ
}
// set debug io
IOWR_ALTERA_AVALON_PIO_DATA(DEBUG_BASE, 1);
// set period
IOWR_ALTERA_AVALON_TIMER_PERIODL(HIRES_TIMER_BASE, 0x03E8);
IOWR_ALTERA_AVALON_TIMER_PERIODH(HIRES_TIMER_BASE, 0x0000);
// Start timer, single, with IRQ
IOWR_ALTERA_AVALON_TIMER_CONTROL(HIRES_TIMER_BASE, 0x0005);
6 Replies
Altera_ForumWhen using a timer as a one shot, you need to write the wanted delay in the snapshot counter registers, not the period registers.
When you send the "start" command, the timer counts down from the value currently stored in the snapshot counter. The period value is only copied in the counter once the counter reaches 0.- Altera_Forum
Hi Daixiwen,
although for me a "snapshot" is like a snapshot (like photography) of the timer count, now i know why there is also a write to those registers. Maybe my englisch isn't good enough. I will try that as soon as possible. Thanks you for your reply - Altera_Forum
English isn't my mother tongue either but I agree that "snapshot" is a poor choice of words in that case. If you check the timer's datasheet you will see that they are read/write registers.
- Altera_Forum
Ok, I tried to do it like this:
and then also like this:// set on shot time IOWR_ALTERA_AVALON_TIMER_SNAPL(HIRES_TIMER_BASE, 0x03E8); IOWR_ALTERA_AVALON_TIMER_SNAPH(HIRES_TIMER_BASE, 0x0000); // Start timer, single, with IRQ IOWR_ALTERA_AVALON_TIMER_CONTROL(HIRES_TIMER_BASE, 0x0005);
always with the same behavour, about 6 to 8us until the IRQ is served.... In the data sheet it is written on the control register bit CONT: "When the counter reaches zero, it reloads with the value stored in the period registers, regardless of the CONT bit" Thus I would assume that with the second shot the time should be right? Also a test with writing a 7 to the Control register witch also enables the CONT bit (continuous) just "activates" the IRQ just once and not every 1000ms??? Is there maybe a problem with the period setting in QSYS? => Set to 1us assuming the timer decrements every 1us meaning with 1000 set to period/snapshot register counter reaches 0 at 1ms.// set on shot time IOWR_ALTERA_AVALON_TIMER_SNAPL(HIRES_TIMER_BASE, 0x03E8); IOWR_ALTERA_AVALON_TIMER_SNAPH(HIRES_TIMER_BASE, 0x0000); IOWR_ALTERA_AVALON_TIMER_PERIODL(HIRES_TIMER_BASE, 0x03E8); IOWR_ALTERA_AVALON_TIMER_PERIODH(HIRES_TIMER_BASE, 0x0000); // Start timer, single, with IRQ IOWR_ALTERA_AVALON_TIMER_CONTROL(HIRES_TIMER_BASE, 0x0005); - Altera_Forum
Yes I think it's a problem with the QSys settings. The value you put in the period and snapshot registers are always expressed in clock cycles. This means that if you have a 80MHz clock, you need to write 80000 to get a 1ms timer. The value you write now is too small for a 1ms delay. The period setting that you set in QSys only sets the initial value of the period register. Remember also to enable the "writeable period" option on so that you have the possibility to modify the period register.
- Altera_Forum
Call me crazy but now i got my time of 1ms while trying several things but i am very surprised of this behaviour. With all those tries i came to the same result as at my first post. As i wrote in my there i also tried with a value of 80'000 in the periodl/h registers. But nothing happened. And I was shure to save all before compiling and starting! For me this is relly crazy i don't understand that. In addition, with a lower count of 1000 the time should be at least above 12.5us.
Now i'm just writing to the period registers 80000 as above and it is working?!? Anyway, thanks a lot for your help. PS: Your definition of a man-year is reminds me on some of my cheefs ;-)
