From ca3e4e0819f6bb60cf7f5c53176de03acdb07ff3 Mon Sep 17 00:00:00 2001 From: imp Date: Sun, 7 Oct 2012 02:08:19 +0000 Subject: Improve a few comments. --- sys/arm/at91/at91_rtc.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'sys/arm/at91') diff --git a/sys/arm/at91/at91_rtc.c b/sys/arm/at91/at91_rtc.c index 71fb367..e7a63a1 100644 --- a/sys/arm/at91/at91_rtc.c +++ b/sys/arm/at91/at91_rtc.c @@ -29,11 +29,13 @@ * * This driver does not currently support alarms, just date and time. * - * Note that on an rm9200 the RTC is not your typical battery-driven clock that - * keeps time while the system is powered down. In fact, it doesn't even - * survive a chip reset to keep time across a reboot. About the only thing it - * might be good for is keeping time while the cpu clock is turned off for power - * savings. On later chips, a battery backup feature is available. + * The RTC on the AT91RM9200 resets when the core rests, so it is useless as a + * source of time (except when the CPU clock is powered down to save power, + * which we don't currently do). On AT91SAM9 chips, the RTC survives chip + * reset, and there's provisions for it to keep time via battery backup if the + * system loses power. On those systems, we use it as a RTC. We tell the two + * apart because the century field is 19 on AT91RM9200 on reset, or on AT91SAM9 + * chips that haven't had their time properly set. */ #include @@ -186,10 +188,13 @@ out: return (err); } +/* + * Cannot support detach, since there's no clock_unregister function. + */ static int at91_rtc_detach(device_t dev) { - return (EBUSY); /* XXX */ + return (EBUSY); } static int -- cgit v1.1