[BRLTTY] BRLTTY in GRUB2

[Vladimir 'φ-coder/phcoder' Serbinenko]

On 22.03.2012 22:23, Dave Mielke wrote:
> [quoted lines by Vladimir 'φ-coder/phcoder' Serbinenko on 2012/03/22 at 20:50 +0100]
>
>> We have common for all platforms:
>> grub_uint64_t grub_get_time_ms (); from<grub/time.h>
>> This gets you 1ms resolution except on i386 if no tsc support is
>> available in this case you get only 55ms resolution but such cpu are
>> rare nowadays.
> But the returned value is still in ms?
Yes
> Is the base value (meaning of 0) truly unknown, or is it something like the
> time when grub was started?
Depends on time source. With TSC source it's supposed to be the time of 
TSC calibration (but because of a bug I don't want to fix until after 
release (it has no consequence) isn't) but at different platforms we use 
different sources and it's often either the power-on time or unspecified.
>   If the latter, does grub save the datetime of when
> it was started, in which case the actual current time in ms could be clculated?
Saving time is possible but the problem is that in order to combine both 
sources into gettimeofday you'd need to synchronise the edge. Otherwise 
you may have the effects like:
{x, 20} -> {x, 21}-> {x+1,22} gives you an impression of whole second 
elapsed in between.
Or even worse
{x,998}->{x,999}->{x,0} which gives you an impression of time going 
backwards.
Additionally the clock skew is different.
Moreover datetime unlike ticks isn't essential for GRUB, even though all 
currently supported platforms provide one.
So I'd prefer if possible not to use datetime in anything which actually 
modifies behaviour, at least per default, and not purely cosmetic (log 
timestamps are cosmetic in GRUB since they are not saved in a file).

>> Also on some platforms you can get better resolution.
> Presumalby, with a different function?
Yes grub_get_rtc. Currently it's used only in clock backend and 
shouldn't used by normal consumers. If higher resolution is desirable a 
function can be introduced but some platforms e.g. ieee1275 provide only 
milliseconds resolution.


-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko