Commit 9491e9bc authored Aug 24, 2015 by Laurent Vivier

i6300esb: remove muldiv64()



Originally, timers were ticks based, and it made sense to
add ticks to current time to know when to trigger an alarm.

But since commit:

74475455 change all other clock references to use nanosecond resolution accessors

All timers use nanoseconds and we need to convert ticks to nanoseconds, by
doing something like:

    y = muldiv64(x, get_ticks_per_sec(), PCI_FREQUENCY)

where x is the number of device ticks and y the number of system ticks.

y is used as nanoseconds in timer functions,
it works because 1 tick is 1 nanosecond.
(get_ticks_per_sec() is 10^9)

But as PCI frequency is 33 MHz, we can also do:

    y = x * 30; /* 33 MHz PCI period is 30 ns */

Which is much more simple.

This implies a 33.333333 MHz PCI frequency,
but this is correct.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>

parent 8a47d575

hw/watchdog/wdt_i6300esb.c

+3 −8

Original line number	Diff line number	Diff line
		@@ -129,14 +129,9 @@ static void i6300esb_restart_timer(I6300State *d, int stage)
		else
		timeout <<= 5;

		/* Get the timeout in units of ticks_per_sec.
		*
		* ticks_per_sec is typically 10^9 == 0x3B9ACA00 (30 bits), with
		* 20 bits of user supplied preload, and 15 bits of scale, the
		* multiply here can exceed 64-bits, before we divide by 33MHz, so
		* we use a higher-precision intermediate result.
		*/
		timeout = muldiv64(timeout, get_ticks_per_sec(), 33000000);
		/* Get the timeout in nanoseconds. */

		timeout = timeout * 30; /* on a PCI bus, 1 tick is 30 ns*/

		i6300esb_debug("stage %d, timeout %" PRIi64 "\n", d->stage, timeout);