Re: Help about MPC823 Video and Cache

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 <redacted>
To: Shuangjun Zhu (r44089) <redacted>; Dan Malek
[off-list ref]
Cc: linuxppc-embedded <redacted>
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. >

quoted

I believe this is caused by the cache being on for the region of memory

used

quoted

for the frame buffer.  You'll see little 16 byte chunks of memory

sparkling as

quoted

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,

quoted

or you can add code to some periodic timer handler to do a DCBF on the

region

quoted

of the frame buffer each time the timer ticks (this is not cheap,

however).

quoted

a

On
Wed, 26 Jan 2000, Shuangjun Zhu wrote: > Hello, everyone

quoted

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/