On Thu, 21 Dec 2017, Programmingkid wrote:
On Dec 21, 2017, at 12:56 PM, BALATON Zoltan email@example.com wrote: On Thu, 21 Dec 2017, Jd Lyons wrote:
On Dec 21, 2017, at 9:59 AM, Programmingkid firstname.lastname@example.org wrote:
On Dec 21, 2017, at 9:36 AM, Jd Lyons email@example.com wrote: I don’t know, this maybe an issue with the way we have defined “us”.
I'm not sure the us word is related to problems with b?branch but I don't know anything about this other than reading the conversation here. They look unrelated to me but it could well be I did not undersand this at all.
Looking through the SLOF code it seems they call it like this in the timebase.fs: : tb@ ( -- tb ) BEGIN tbu@ tbl@ tbu@ rot over <> WHILE 2drop REPEAT 20 lshift swap ffffffff and or ; : milliseconds ( -- ms ) tb@ d# 1000 * tb-frequency / ; : microseconds ( -- us ) tb@ d# 1000000 * tb-frequency / ; : ms ( ms-to-wait -- ) milliseconds + BEGIN milliseconds over >= UNTIL drop ; : get-msecs ( -- n ) milliseconds ; : us ( us-to-wait -- ) microseconds + BEGIN microseconds over >= UNTIL drop ; Not sure if I can port/hack this code over, the copier seems to have trouble with tbu@ tbl@?
The ms and get-msecs words don't appear to be implemented correctly on OpenBIOS. 10000 ms should pause OpenBIOS for 10 seconds. It does not. I did find a function called udelay() in the drivers/timer.c file. Maybe I can implement the word us using udelay(). Then the ms word could be implemented using the us word.
See what you can do about : us, but we maybe running into an issue with Qemu/mac99. Every version of the Mac OS reports a different bus and cpu speed, so we maybe having trouble with the way the timebase is calculated in Qemu.
I think you have two choices for this:
- Either export udelay (or _wait_ticks it's based on) to Forth and
implement these words based on that. But this comment in drivers/timer.c:
How would I do this?
- TODO: pass via lb table
*/ unsigned long timer_freq = 10000000 / 4;
suggests you may need to fix this first to take into accound the actual TB frequency from the CPU instead of some hardcoded value.
This would make a good next step.
- Alternatively, you could either add new helpers (maybe in
arch/ppc/timebase.S) to implement tbl@ and tbu@ which probably should just do mftb and mftbu respectively or export to Forth the already existing _get_ticks which returns these as a combined 64 bit value and derive the lower and upper 32 bits from Forth and then maybe you can use the above implementation from SLOF.
It is a possibility.
We still need a way to access any new C function from forth. The only thing that I think would work is implementing the us word in a device node, then make another definition of us that is available to the dictionary. If anyone has a way to do this, an example would be great.
I don't know much about this but looking at the code I think _get_ticks is almost equivalent to tb@ above except that _get_ticks returns tbu@ in %r3 and tbl@ in %r4 but tb@ also combines these into one value. Then you can see e.g. in arch/ppc/qemu/init.c that the bind_func() function is used to make C functions available from Forth. So you could make a C function which calls _get_ticks then combines %r3 and %r4 into a 64bit value (so implements what tb@ does in C) then bind this to tb@. Or bind _get_ticks and implement tb@ calling this and combining the upper and lower values from Forth like above (I think this is what '20 lshift swap ffffffff and or' does but I don't know Forth to tell).
You'll also need tb-frequency which can be found in the cpu properties (added in arch/ppc/qemu/init.c by reading the correct value from QEMU). SLOF has a function that seems to be called during init but I can't read Forth enough to tell for sure what it actually does:
\ Fixup timebase frequency from device-tree : fixup-tbfreq " /cpus/@0" find-device " timebase-frequency" get-node get-package-property IF 2drop ELSE decode-int to tb-frequency 2drop THEN device-end ; fixup-tbfreq
But I think this is what sets tb-frequency global value so you'll probably need something similar somewhere (maybe ppc.fs). Then you have tb@ and tb-frequency so the rest should work.
Now it's your turn to find out how to do this in OpenBIOS.
Regards, BALATON Zoltan