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Wade Maxfield wrote:
<blockquote
cite="mid45a1b53e0608210651s4f5de382w77e092463dbbf5b7@mail.gmail.com"
type="cite"><br>
I'm new to the PPC and I have a few questions. I have written a
driver in the past for the X86 family, using i/o ports, but it was
kernel 2.0 and i/o ports are not mmu handled.<br>
I've been looking through the archive and I am slowly growing more
confused. <br>
</blockquote>
The PPC MMU is pretty simple compared to the x86.<br>
Basically the MMU unit is a peice of hardware that maps "virtual"
addresses to "physical" addresses.<br>
Its use is enabled/disabled by two bits in the PPC Machine Status
register - 1 for instructions, 1 for data.<br>
The MMU itself is basically a 64 entry lookup table. Virtual
address X corresponds to physical address Y.<br>
When a request is made for an address that is not in the 64 entry
MMU table things become more complex<br>
- an exception is generated and code inside Linux searches its
tables to find the correct entry to stuff into the MMU.<br>
NORMALLY there is no correspondence between physical addresses and
virtual ones. But it is possible (and might be useful for debugging) to
stuff an entry <br>
where physical=virtual. If you look inside head_4xx.S for
CONFIG_SERIAL_TEXT_DEBUG or something like that you should see how to
do it.<br>
However manually stuffed entries in the MMU will eventually get
blown away. I spent a week trying to trace a problem caused by that
down.<br>
<br>
<br>
<blockquote
cite="mid45a1b53e0608210651s4f5de382w77e092463dbbf5b7@mail.gmail.com"
type="cite"><br>
We are using Xilinx with PPC built in.<br>
<br>
The PPC has a memory management unit. All of the IP we've added is
mapped to physical addresses.<br>
<br>
1. Can I access the memory the peripherasl are mapped to directly
within the driver without going through functions? <br>
if NOT, then Do I use <br>
1. ioremap(), <br>
</blockquote>
Once you have done the ioremap(), you can use the address returned
exactly the way you would have used the physical address previously.<br>
<br>
<br>
<blockquote
cite="mid45a1b53e0608210651s4f5de382w77e092463dbbf5b7@mail.gmail.com"
type="cite"> 2. request_mem_region(), <br>
3. request_region()<br>
4. something else?<br>
<br>
2. Are there any gotcha's with the ppc 405 that Xilinx uses that I
should know about?
<br>
</blockquote>
Are you doing board bringup ? <br>
If you are not bringing up a new board - then the big gotcha's
should already be covered.<br>
If you are doing board bringup - I would recommend following the
existing xilinx packages closely. <br>
<blockquote
cite="mid45a1b53e0608210651s4f5de382w77e092463dbbf5b7@mail.gmail.com"
type="cite"><br>
<br>
thanks,<br>
wade<br>
<br>
<br>
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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Dave Lynch DLA Systems
Software Development: Embedded Linux
717.627.3770 <a class="moz-txt-link-abbreviated" href="mailto:dhlii@dlasys.net">dhlii@dlasys.net</a> <a class="moz-txt-link-freetext" href="http://www.dlasys.net">http://www.dlasys.net</a>
fax: 1.253.369.9244 Cell: 1.717.587.7774
Over 25 years' experience in platforms, languages, and technologies too numerous to list.
"Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction."
Albert Einstein
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