Hi Remy,
Thank you for clarifying the setup.
The TC-block example was just what I was looking for.
I have the timer working so I'll give it a try and see if I
can fit it for our system.
Thank you for your time.
Best regards,
Bo
Remy Bohmer wrote:
Hi,
The Timer counter library sounds interesting - I previously took a look
at the source, but I miss some examples of how to use it. Do you know
anywhere I can find some beside tcb_clksrc.c?
Mailinglist archives?
But here is an example that produces a 400Hz (configurable) interrupt.
-------------------------------------------------------------------------------------
#include <linux/atmel_tc.h>
static struct atmel_tc *tc;
static int tc_clk_id = 0; /* 0..2 (3 timers per TC-block) */
static int tc_blk_id = 1; /* 0..1 (2 TC-blocks on rm9200,
0 is used by clocksrc/clockevent */
static int tc_timer_freq = 400; /* HZ */
static irqreturn_t tc_timer_interrupt(int irq, void *dummy)
{
void __iomem *tcaddr = tc->regs;
unsigned int sr = __raw_readl(tcaddr + ATMEL_TC_REG(tc_clk_id, SR));
if (sr & ATMEL_TC_CPCS) {
wakeup_my_thread(); /* Here you must wakeup your
RT-thread (use wake_up_process() !!! )*/
return IRQ_HANDLED;
}
return IRQ_NONE;
}
static struct irqaction tc_irqaction = {
.name = "periodic-tc-timer",
.flags = IRQF_NODELAY | IRQF_DISABLED,
.handler = tc_timer_interrupt,
};
void install_tc_periodic_interrupt(void)
{
void __iomem *tcaddr;
int rate;
int res;
/* allocate the timer block */
tc = atmel_tc_alloc(tc_blk_id, tc_irqaction.name);
if (!tc) {
printk(KERN_ERR "can't alloc TC\n");
return -ENODEV;
}
tcaddr = tc->regs;
res = setup_irq(tc->irq[tc_clk_id], &tc_irqaction);
if (res) {
printk(KERN_ERR "%s: Failed to install timer interrupt:%i\n",
__func__, res);
return res;
}
clk_enable(tc->clk[tc_clk_id]);
rate = clk_get_rate(tc->clk[tc_clk_id]);
/* Stop only the timer we will use */
__raw_writel(0xff, tcaddr + ATMEL_TC_REG(tc_clk_id, IDR));
__raw_writel(ATMEL_TC_CLKDIS, tcaddr + ATMEL_TC_REG(tc_clk_id, CCR));
/* Use MCK/8 (->CLOCK2), count up to RC, then irq and restart */
__raw_writel(ATMEL_TC_TIMER_CLOCK2
| ATMEL_TC_WAVE | ATMEL_TC_WAVESEL_UP_AUTO,
tcaddr + ATMEL_TC_REG(tc_clk_id, CMR));
__raw_writel((rate/8) / tc_timer_freq,
tcaddr + ATMEL_TC_REG(tc_clk_id, RC));
/* Enable clock and interrupts on RC compare */
__raw_writel(ATMEL_TC_CPCS, tcaddr + ATMEL_TC_REG(tc_clk_id, IER));
/* go go gadget! */
__raw_writel(ATMEL_TC_CLKEN | ATMEL_TC_SWTRG,
tcaddr + ATMEL_TC_REG(tc_clk_id, CCR));
printk(KERN_INFO "TC interrupt source installed.\n");
}
-------------------------------------------------------------------------------------
Correct me if I'm wrong but using TC you still have the RT patch applied,
but just disabled HRT/dynticks?
Yes indeed. We use the RT-patch on these processors without
HRT/dynticks. We only use the OS/Posix-timers for non-realtime
applications, so CONFIG_HZ can be set low to reduce the timer
interrupt load.
Do you have any idea of the overhead of TC@1ms compared with
CONFIG_HZ=1000?
The difference between the 2 is that the kernel does not need to
handle all the elapsed timers on every timer interrupt, but instead
just waking up a single thread.
FYI, I made measurements of it some time ago that shows what happens
on a single timer interrupt on this processor, and I attached a
screenshot to this mail.
Have fun!
Remy
------------------------------------------------------------------------
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