Help about MPC823 Video and Cache

Help about MPC823 Video and Cache

[Shuangjun Zhu]

Hello, everyone

I'm using kernel version 2.2.13 on my MPC823 FADS board
to display on TV. I have a problem:

After the system boot up, the text on the TV flicker fiercely out,
if I disable the I-Cache throught the EST visionProbe tool,
TV will not flicker out again.
Of course, if I disable the cache when the system boot up,
TV display OK.
So there is some relation between the cache and the video, I guess.


Do you have any suggestion?
Thanks in advacned!

BRs,
Shuangjun

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Re: Help about MPC823 Video and Cache

[Alan Mimms]

We experimented at Apple with cacheable frame buffers and this is what we saw.

I believe this is caused by the cache being on for the region of memory used
for the frame buffer.  You'll see little 16 byte chunks of memory sparkling as
the cache finally dumps out dirty cache lines into the real frame buffer.

You can fix this by mapping the area of the frame buffer with cache disabled,
or you can add code to some periodic timer handler to do a DCBF on the region
of the frame buffer each time the timer ticks (this is not cheap, however).

a

On
Wed, 26 Jan 2000, Shuangjun Zhu wrote: > Hello, everyone
>
> I'm using kernel version 2.2.13 on my MPC823 FADS board
> to display on TV. I have a problem:
>
> After the system boot up, the text on the TV flicker fiercely out,
> if I disable the I-Cache throught the EST visionProbe tool,
> TV will not flicker out again.
> Of course, if I disable the cache when the system boot up,
> TV display OK.
> So there is some relation between the cache and the video, I guess.
>
>
> Do you have any suggestion?
> Thanks in advacned!
>
> BRs,
> Shuangjun
--
Alan Mimms     Packet Engines, Inc.     Spokane, Washington [99214-0497]
  USA, Earth, Sol, Milky Way, The Local Group, Virgo Supercluster, U0
Despite the cost of living, have you noticed how popular it remains?
  -- Steven Wright?

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: Help about MPC823 Video and Cache

[Alan Mimms]

Forgot this: One more possibility is to make the frame buffer region of address
space cacheable but write-thru rather than copy-back.

a

On Wed, 26 Jan 2000, Alan Mimms wrote: > We experimented at Apple with
cacheable frame buffers and this is what we saw. >
> I believe this is caused by the cache being on for the region of memory used
> for the frame buffer.  You'll see little 16 byte chunks of memory sparkling as
> the cache finally dumps out dirty cache lines into the real frame buffer.
>
> You can fix this by mapping the area of the frame buffer with cache disabled,
> or you can add code to some periodic timer handler to do a DCBF on the region
> of the frame buffer each time the timer ticks (this is not cheap, however).
>
> a
>
> On
> Wed, 26 Jan 2000, Shuangjun Zhu wrote: > Hello, everyone
> >
> > I'm using kernel version 2.2.13 on my MPC823 FADS board
> > to display on TV. I have a problem:
> >
> > After the system boot up, the text on the TV flicker fiercely out,
> > if I disable the I-Cache throught the EST visionProbe tool,
> > TV will not flicker out again.
> > Of course, if I disable the cache when the system boot up,
> > TV display OK.
> > So there is some relation between the cache and the video, I guess.
> >
> >
> > Do you have any suggestion?
> > Thanks in advacned!
> >
> > BRs,
> > Shuangjun
> --
> Alan Mimms     Packet Engines, Inc.     Spokane, Washington [99214-0497]
>   USA, Earth, Sol, Milky Way, The Local Group, Virgo Supercluster, U0
> Despite the cost of living, have you noticed how popular it remains?
>   -- Steven Wright?
--
Alan Mimms     Packet Engines, Inc.     Spokane, Washington [99214-0497]
  USA, Earth, Sol, Milky Way, The Local Group, Virgo Supercluster, U0
Despite the cost of living, have you noticed how popular it remains?
  -- Steven Wright?

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: Help about MPC823 Video and Cache

[Dan Malek]

Shuangjun Zhu wrote:

> After the system boot up, the text on the TV flicker fiercely out,
> if I disable the I-Cache throught the EST visionProbe tool,

Determine your silicon revision and look on the Motorola web
site for errata and application notes.  Early versions of the
823 didn't work so well, especially at high resolution and
refresh rates.  Later versions of the 823 added somewhat
undocumented SIU configurations to improve the arbitration of
the U-bus and access to the frame buffer by the video controller.

If all seems well on the silicon front, make sure your video
configuration is proper.  Excessively high (and unnecessary)
refresh rates cause problems.


	-- Dan

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Re: Help about MPC823 Video and Cache

[Shuangjun Zhu]

Alan,

Thanks,
More important, in my program, I througth following code to disable the
cache
for the display buffer memory:
============================================================================
 for (i=0,mem_addr=__va(video_fb_base);i<num_video_pages;i++) {
                pte = va_to_pte(&init_task, mem_addr);
                pte_val(*pte) |= _PAGE_NO_CACHE;
                flush_tlb_page(current->mm->mmap, mem_addr);
  mem_addr += PAGE_SIZE;
 }
============================================================================
Is it right?

Through the debug tool (EST visionProbe), if I just disable the I-Cache,
TV display almost OK, and disable the D-Cache and I-Cache both, it's
very well, but if I modify from write-through to write-back,
effection is not notable.

BRs,
Shuangjun


-----Original Message-----
From: Alan Mimms <alan@packetengines.com>
To: Shuangjun Zhu (r44089) <r44089@email.sps.mot.com>; Dan Malek
<dan@netx4.com>
Cc: linuxppc-embedded <linuxppc-embedded@lists.linuxppc.org>
Date: Thursday, January 27, 2000 9:26 AM
Subject: Re: Help about MPC823 Video and Cache


>Forgot this: One more possibility is to make the frame buffer region of
address
>space cacheable but write-thru rather than copy-back.
>
>a
>
>On Wed, 26 Jan 2000, Alan Mimms wrote: > We experimented at Apple with
>cacheable frame buffers and this is what we saw. >
>> I believe this is caused by the cache being on for the region of memory
used
>> for the frame buffer.  You'll see little 16 byte chunks of memory
sparkling as
>> the cache finally dumps out dirty cache lines into the real frame buffer.
>>
>> You can fix this by mapping the area of the frame buffer with cache
disabled,
>> or you can add code to some periodic timer handler to do a DCBF on the
region
>> of the frame buffer each time the timer ticks (this is not cheap,
however).
>>
>> a
>>
>> On
>> Wed, 26 Jan 2000, Shuangjun Zhu wrote: > Hello, everyone
>> >
>> > I'm using kernel version 2.2.13 on my MPC823 FADS board
>> > to display on TV. I have a problem:
>> >
>> > After the system boot up, the text on the TV flicker fiercely out,
>> > if I disable the I-Cache throught the EST visionProbe tool,
>> > TV will not flicker out again.
>> > Of course, if I disable the cache when the system boot up,
>> > TV display OK.
>> > So there is some relation between the cache and the video, I guess.
>> >
>> >
>> > Do you have any suggestion?
>> > Thanks in advacned!
>> >
>> > BRs,
>> > Shuangjun
>> --
>> Alan Mimms     Packet Engines, Inc.     Spokane, Washington [99214-0497]
>>   USA, Earth, Sol, Milky Way, The Local Group, Virgo Supercluster, U0
>> Despite the cost of living, have you noticed how popular it remains?
>>   -- Steven Wright?
>--
>Alan Mimms     Packet Engines, Inc.     Spokane, Washington [99214-0497]
>  USA, Earth, Sol, Milky Way, The Local Group, Virgo Supercluster, U0
>Despite the cost of living, have you noticed how popular it remains?
>  -- Steven Wright?
>


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