FPGA registers userspace interface?

FPGA registers userspace interface?

[Kfir Lavi]

Hi,
I have a FPGA that is constantly changing (its on development phase).
I want to let userspace app to update those registers, but don't want to
create an API yet.
What is the best way to open a range of registers to userspace, so no driver
update is required?

Thanks,
Kfir
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FPGA registers userspace interface?

[Daniel Baluta]

On Mon, Jan 3, 2011 at 2:47 PM, Kfir Lavi <lavi.kfir@gmail.com> wrote:
> Hi,
> I have a FPGA that is constantly changing (its on development phase).
> I want to let userspace app to update those registers, but don't want to
> create an API yet.
> What is the best way to open a range of registers to userspace, so no driver
> update is required?

You can think of exporting them via sysfs, together with some additional
information like register base address.

thanks,
Daniel.

FPGA registers userspace interface?

[Philip Downer]

On 03/01/11 12:47, Kfir Lavi wrote:

> I have a FPGA that is constantly changing (its on development phase).
> I want to let userspace app to update those registers, but don't want to
> create an API yet.
> What is the best way to open a range of registers to userspace, so no
> driver update is required?

When I had to do this recently I used sysfs, I have no idea if it's the 
best way but it certainly was very effective. Remember in sysfs that 
each file should only have one value.

Once it's setup though you can just write to the sysfs files, I started 
by writing simple perl scripts to test things before starting to write 
more complex apps.

HTH

Phil

FPGA registers userspace interface?

[Kfir Lavi]

On Mon, Jan 3, 2011 at 3:00 PM, Philip Downer <phil@pjd.me.uk> wrote:

> On 03/01/11 12:47, Kfir Lavi wrote:
>
>  I have a FPGA that is constantly changing (its on development phase).
>> I want to let userspace app to update those registers, but don't want to
>> create an API yet.
>> What is the best way to open a range of registers to userspace, so no
>> driver update is required?
>>
>
> When I had to do this recently I used sysfs, I have no idea if it's the
> best way but it certainly was very effective. Remember in sysfs that each
> file should only have one value.
>
> Once it's setup though you can just write to the sysfs files, I started by
> writing simple perl scripts to test things before starting to write more
> complex apps.
>
> HTH
>
> Phil
>
So what do expose in sysfs? for each register - a file of it's own? or you
get a bulk of data to one file?

Thanks,
Kfir
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FPGA registers userspace interface?

[Kfir Lavi]

On Mon, Jan 3, 2011 at 5:09 PM, Kfir Lavi <lavi.kfir@gmail.com> wrote:

>
>
> On Mon, Jan 3, 2011 at 3:00 PM, Philip Downer <phil@pjd.me.uk> wrote:
>
>> On 03/01/11 12:47, Kfir Lavi wrote:
>>
>>  I have a FPGA that is constantly changing (its on development phase).
>>> I want to let userspace app to update those registers, but don't want to
>>> create an API yet.
>>> What is the best way to open a range of registers to userspace, so no
>>> driver update is required?
>>>
>>
>> When I had to do this recently I used sysfs, I have no idea if it's the
>> best way but it certainly was very effective. Remember in sysfs that each
>> file should only have one value.
>>
>> Once it's setup though you can just write to the sysfs files, I started by
>> writing simple perl scripts to test things before starting to write more
>> complex apps.
>>
>> HTH
>>
>> Phil
>>
> So what do expose in sysfs? for each register - a file of it's own? or you
> get a bulk of data to one file?
>
> Thanks,
> Kfir
>

I thought about using 3 files in sysfs.
1. address of the register
2. data to write to the register
3. trigger that do the write

Please share your comments.
Regards,
Kfir
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FPGA registers userspace interface?

[Daniel Baluta]

> I thought about using 3 files in sysfs.
> 1. address of the register
> 2. data to write to the register
> 3. trigger that do the write

The most effective solution would be to
have one file per register.

Writing register:
# echo value > /sys/path/to/file

Reading register:
# cat /sys/path/to/file

Also, since your FPGA is in development phase I assume that
the registers base address is changing (or am I wrong?). You can
solve this with an additional writable sysfs entry  which will
hold the current base address.

thanks,
Daniel.

FPGA registers userspace interface?

[Greg KH]

On Mon, Jan 03, 2011 at 10:52:34PM +0200, Daniel Baluta wrote:
> > I thought about using 3 files in sysfs.
> > 1. address of the register
> > 2. data to write to the register
> > 3. trigger that do the write
> 
> The most effective solution would be to
> have one file per register.
> 
> Writing register:
> # echo value > /sys/path/to/file
> 
> Reading register:
> # cat /sys/path/to/file
> 
> Also, since your FPGA is in development phase I assume that
> the registers base address is changing (or am I wrong?). You can
> solve this with an additional writable sysfs entry  which will
> hold the current base address.

Also remember that debugfs would also be good for something like this,
being much easier to use than sysfs.

Note the rule when using debugfs:
	There is are no rules when using debugfs.

Which works much better when doing development :)

thanks,

greg k-h