Re: [microblaze-uclinux] Writing Drivers

[Aurash <aurelian.lazarut@xxxxxxxxxxx>]

Hi all,
I just want to second John's (and others) advice to use the "Linux 
device drivers" book (Rubini & Corbet) a very good book, and you can 
download all the code examples presented in the book from 
http://examples.oreilly.com/linuxdrive3/
another point, is good to have "Understanding the Linux Kernel" (Daniel 
p. Bovet & Marco Cesati) from O'Reilly and "Building Embedded Linux 
Systems"  (by Yaghmour) I remeber that John was recomending these 3 
books on the MB uC-linux page, I bought them, and are making all the money!

John Williams wrote:

> Hi John,
>
> John McGrath wrote:
>
>> Does anyone here have experience with writing their own drivers for 
>> uClinux. I have a peripheral on the OPB, and it is essentially a 
>> memory interface - i.e. register style based. with no OS I can 
>> control it directly by addressing the memory locations in the 
>> following way
>>
>> int main()
>> {
>>   volatile int *my_device = BASE_ADDRESS;
>>     my_device[0] = some_data;
>>
>>   .....
>> }
>>
>> And this will work quite nicely.
>>
>> However I'm sure this hackery will not work in uClinux. So how does 
>> someone write a driver in a "standard way". I guess uClinux does 
>> things like re-mapping the physical address, etc, for its own 
>> reasons, and the driver would have to support this?
>> I guess put more simply - if you wanted to write a driver for a bram 
>> block, how would you do it?
>
>
> In fact, under uClinux you can write directly to memory, IO space, 
> whatever you like.  This is because there is no MMU.  However, the 
> question is whether you should. 

Probably not, it works for quick debug, but the sky will fall in your 
head if you have multiple instances (processes) working this way in the 
same time.

>
>
> The ability for use-space direct-writes is certainyl conveninet when 
> debugging new cores - I have even written myself trivial "peek" and 
> "poke" applicatioss that I can run from the shell, for exactly that 
> purpose.
>
> For a purely memory mapped device (no interrupts or tricky kernel 
> threads etc) you can just use the mmap() system call in userspace, 
> then just write directly to the opinter returned.  Under uClinux, 
> mmap() is doing essentially nothing, however at least it is one level 
> "cleaner" than direct writes like in your example.  Also, this 
> approach would work under Linux with an MMU, should you ever migrate 
> in that direction. For an example of accessing hardaware in this way, 
> check out the custom hardware tutorial from Phillip Leong at the 
> Chiniese University of Hong Kong - there is a link in the "news" 
> section on the front paeg of the website.
>
>> Once the basic driver interface is there, I can think about building 
>> the more user-friendy functions around it.
>>
>> Also, I would like to add interrupts, and a handler for it in the 
>> driver. Its not necessary, but definalty a nice to have...is this 
>> difficult?
>
>
> If you need all of this, you must write a standard kernelmode device 
> driver.  This is not necessarily difficult, but there's certainly a 
> bit of a learning curve.  Corbet and Rubini's "Linux Device Drivers" 
> (2nd edition) from O'Reilly is the one you want.  I think the 
> full-text is available on-line.
>
> The good nwes is there are thousands of examples in the sources 
> already.  It's usually a case of finding one that has the same broad 
> structure of what you are tring to achieev, then modifying to your needs.
>
>> Btw - on a completly unrealted note - I got uclinux running under 
>> 7.1i - with MB version 4.00a. I had the FPU enabled, but I guess the 
>> toolchain doesnt support it.
>
>
> The custom toolchain is still from EDK6.3 - so no it does not know 
> about the FPU.  I am fionalisding support for uClinux builds under the 
> "native" toolchain distributed with 7.1 - should be some updates soon 
> on that.
>
> Regards,
>
> John

All the best,
Aurash

>
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