Op wo 21 nov. 2018 om 00:13 schreef Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>:
On Tue, 20 Nov 2018, Kars de Jong wrote:
Op ma 19 nov. 2018 om 02:10 schreef Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>:
hp300_gettimeoffset() never checks the timer interrupt flag and will
fail to notice when the timer counter gets reloaded. That means the
clock could jump backwards.
Remove this code and leave this platform on the 'jiffies' clocksource.
Note that this amounts to a regression in clock precision. However,
adopting the 'jiffies' clocksource does resolve the monotonicity issue.
Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
---
hp300_gettimeoffset() cannot be used in a clocksource conversion
unless it can be made monotonic. I can't fix this without knowing the
details of the timer implementation, such as the relationship between
the timer count and the interrupt flag.
I don't really like this regression...
Me neither...
I'll see if I can write a conversion patch based on the information you've
provided. Can you test it?
I can try... It's been a while since I booted the machine to Linux
though (NFS support only).
MAME is also starting to support it, but not quite there yet :-)
According to NetBSD sources, there are 3 timers in the chip (originally
an MC6840 PTM).
Thanks for the tip. I will examine the datasheet for the 6840.
I'll also take another look at the NetBSD code.
Timer 1 is used as the system timer, timer 3 runs at the same rate and
is unused on Linux (on NetBSD it is used as the statistics/profiling
timer), and timer 3 is connected to timer 2 so you can make a 32-bit
timer out of the two timers together (also unused on Linux).
Timers 1 counts down at 25 MHz.
You mean, 250 kHz, right? The code in mainline programs the timer for 2500
cycles, hoping to get 10 ms. That is, 250 cycles per ms.
Eh, yes, that makes a lot more sense.
The interrupt flag is set when the counter reaches 0 after which it is
automatically reloaded and starts counting down again.
Thanks.
On atari, the 68901 counts down to 0x01 and raises an interrupt. On mac,
the 6522 counts down to 0xFFFF then raises an interrupt. No idea about
amiga (Geert?) -- this has to be handled correctly to get a monotonic
clocksource. I'll fix this in v3 (where the information is available).
Cool!
Kars.
