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SubjectLinuxPPS low-level IRQs timestamps & ldisc
Hello,

I write to both of you since my questions are related. :)

My last modifications to LinuxPPS are focused on adding a PPS ldisc
and a low-level IRQs timestamps recording.

First I added a new dcd_change() ldisc method which can be used as
follow:

static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status)
{
int id = (int) tty->disc_data;
struct timespec __ts;
struct pps_ktime ts;

/* First of all we get the time stamp... */
getnstimeofday(&__ts);

/* ... and translate it to PPS time data struct */
ts.sec = __ts.tv_sec;
ts.nsec = __ts.tv_nsec;

/* Now do the PPS event report */
pps_event(id, &ts,
status ? PPS_CAPTUREASSERT : PPS_CAPTURECLEAR, tty);

pr_debug("[STDev] PPS %s at %lu on source #%d\n",
status ? "assert" : "clear", jiffies, id);
}

However this solution gives very low precision timestamps so that's
why I propose to add the following code to register IRQ timestamps as
soon as possible (here the code for x86_32 architecture):

diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index d3fde94..a3b8457 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -15,6 +15,7 @@
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/delay.h>
+#include <linux/pps.h>

#include <asm/apic.h>
#include <asm/uaccess.h>
@@ -25,6 +26,11 @@ EXPORT_PER_CPU_SYMBOL(irq_stat);
DEFINE_PER_CPU(struct pt_regs *, irq_regs);
EXPORT_PER_CPU_SYMBOL(irq_regs);

+#ifdef CONFIG_PPS_IRQ_EVENTS
+struct pps_ktime pps_irq_ts[NR_IRQS];
+EXPORT_SYMBOL(pps_irq_ts);
+#endif
+
/*
* 'what should we do if we get a hw irq event on an illegal vector'.
* each architecture has to answer this themselves.
@@ -76,6 +82,12 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
union irq_ctx *curctx, *irqctx;
u32 *isp;
#endif
+#ifdef CONFIG_PPS_IRQ_EVENTS
+ struct timespec __ts;
+
+ /* Get IRQ timestamps as soon as possible for the PPS layer */
+ getnstimeofday(&__ts);
+#endif

if (unlikely((unsigned)irq >= NR_IRQS)) {
printk(KERN_EMERG "%s: cannot handle IRQ %d\n",
@@ -83,6 +95,12 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
BUG();
}

+#ifdef CONFIG_PPS_IRQ_EVENTS
+ /* Then, after sanity check, store the IRQ timestamp */
+ pps_irq_ts[irq].sec = __ts.tv_sec;
+ pps_irq_ts[irq].nsec = __ts.tv_nsec;
+#endif
+
old_regs = set_irq_regs(regs);
irq_enter();
#ifdef CONFIG_DEBUG_STACKOVERFLOW
This allow the following modifications to the dcd_change() method:

static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int irq,
unsigned int status)
{
int id = (int) tty->disc_data;
pps_event(id, &pps_irq_ts[irq],
status ? PPS_CAPTUREASSERT : PPS_CAPTURECLEAR, tty);

pr_debug("[IRQev] PPS %s at %lu on source #%d\n",
status ? "assert" : "clear", jiffies, id);
}
Note that in this case I need also the "irq" parameter.

This solution gives very high timestamps precision! Better that
before! :D

What do you think about this solution? More precisely:

1) The low-level IRQ patch can be acceptable?

2) The new dcd_change() method is well implemented? Can I add the
"irq" parameter or I can find it somewhere?

Thanks a lot for your suggestions,

Rodolfo

--

GNU/Linux Solutions e-mail: giometti@enneenne.com
Linux Device Driver giometti@linux.it
Embedded Systems phone: +39 349 2432127
UNIX programming skype: rodolfo.giometti


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