[OpenBIOS] b?branch

Programmingkid programmingkidx at gmail.com
Fri Dec 22 04:04:36 CET 2017

> On Dec 21, 2017, at 8:52 PM, Jd Lyons <lyons_dj at yahoo.com> wrote:
>> On Dec 21, 2017, at 6:51 PM, BALATON Zoltan <balaton at eik.bme.hu> wrote:
>> On Thu, 21 Dec 2017, Programmingkid wrote:
>>>> On Dec 21, 2017, at 12:56 PM, BALATON Zoltan <balaton at eik.bme.hu> wrote:
>>>> On Thu, 21 Dec 2017, Jd Lyons wrote:
>>>>>> On Dec 21, 2017, at 9:59 AM, Programmingkid <programmingkidx at gmail.com> wrote:
>>>>>>> On Dec 21, 2017, at 9:36 AM, Jd Lyons <lyons_dj at yahoo.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:
>>>> 1. 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.
>>>> 2. 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 at . 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
> Thanks Balaton, that seem pretty clear.
> PK, I’ll be heading out for a few days, hope you have a good holiday, we can pick this up latter. 

Ok. Enjoy your break. If I come up with anything I will report it here.

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