RE: [microblaze-uclinux] Low level access

["Steve Spano" <steve@xxxxxxxxxx>]

Hi

A lot of real Linux guys will disagree here, but my 'thought' process on
uCLinux is to "ride" a standard application ontop of the feature set
(i.e. tcp/ip/etc) that uCLinux brings to the table.

A lot of legacy applications have been ported to uCLinux for various
platforms we have worked on.

For example, lets say you want to light an LED from an application.

If you have a real Linux with MMU, then you need a driver/etc to get to
the kernel and access a hardware port.

I love uCLinux because I can do this.

*(volatile unsigned long*)HARDWAREADDRESS = 0x55

to set the leds located at HARDWAREADDRESS to 0x55. 

Or 

STATUS=*(volatile unsigned long*)STATUSADDRESS

To read a value.

These assume a 32-bit location.

You could do *(volatile unsigned short*) or *(volatile unsigned char*)
for 16 and 8 bit access as well.

I don't like O/S's telling me where I can and cannot write to in the
memory space - we never have pointer reference problems :)

Steve Spano
FLE

-----Original Message-----
From: owner-microblaze-uclinux@xxxxxxxxxxxxxx
[mailto:owner-microblaze-uclinux@xxxxxxxxxxxxxx] On Behalf Of Duy-Ky
Nguyen
Sent: Friday, September 07, 2007 12:52 AM
To: microblaze-uclinux@xxxxxxxxxxxxxx
Subject: RE: [microblaze-uclinux] Low level access

Hello Benny,

You got the point.

My point is, in the old days where many human users shared only 1 CPU.
Being huamn means being err. If s/he made mistake, his/her job must be
shut
down for the sake of others.

That kind of thing become less important for a Linux PC, a
general-purpose
computer.

But, for a special-purpose one, an embeded system, in some cases, it's
very
likely the system must be shutdown even if only 1 task misbehave.
Otherwise,
it could be a disaster.
That's why there's always a redundant computer backup in some critical
systems.

In general, nothing is perfect. Everything has both upside and downside.
People should not overdo, nor undo anything. But it's very chalenging to
do
just right ;-( ;-(
If we pick the most convenience working for ourselve, it's likely we
work in
the best mood, hence less prone to err. To me, the least code is the
best as
bug probability is proportinal to the code size. As usual, I could be
wrong
!

Anyway, I may have made a little progrss in both ways high and low level
access ;-) ;-)

 Cheers,

Duy-Ky

-----Original Message-----
From: owner-microblaze-uclinux@xxxxxxxxxxxxxx
[mailto:owner-microblaze-uclinux@xxxxxxxxxxxxxx] On Behalf Of Benny Chen
Sent: Thursday, September 06, 2007 6:25 PM
To: microblaze-uclinux@xxxxxxxxxxxxxx
Subject: Re: [microblaze-uclinux] Low level access

Hi Duy-ky,
Without hardware MMU support it is even more important for your
application
code to access your ipcore via the IOCTL() command.  This is so because
it
would help prevent your application code from bringing down the kernel
when
it does incorrect memory access due to pointer referencing error.

The recommended way is to write a thin driver for your ipcore and
provide
access to the application program via the device file interface.

If you like the idea of referencing memory via their address instead of
IOCTL then look at mmap() support for your driver.

Cheers,
B,

Duy-Ky Nguyen wrote:
> Hello,
>
> I got some experiences on low level access in Linux using X86 and 
> MPC8272. They were "real Linux" with memory protection between kernel 
> and user space, so I had to go through ioctl for low level access.
>
> I'm quite aware that uCLinux does not have that kind of protection. In

> experience, loose something goes together with gain some thing, so I 
> expect I'm able to have more direct access of low level.
>
> Let's say I have a user_ip at 0x40080000, I've created a new myapp_hw 
> in user-apps, and failed to compile a code using
>
> // Start of code
> #include <asm/io.h>
> #define BASEADDR 0x40080000
> . .
> x = inl((volatile unsigned *) (BASEADDR));    // read-only reg
> outl(1, (volatile unsigned *) (BASEADDR));    // write 1 to RWreg
> ..
> // End of code
>
> I had very long list of error from the compilation.
>
> I'd really appreciate if I'd be shown how to use these low-level IO 
> access functions.
>
> Thanks a lot,
>
> Duy-Ky
>
>
>
>
>
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>
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