[OpenBIOS] b?branch

[Programmingkid]

> 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.