Re: [microblaze-uclinux] FSLFIFO driver usage examples

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Simon,

Simon Tam wrote:
> Hi Hans/John,
>
> I have a FSL link between two MB processors. I modified fslcat so that 
> it becomes a receiver (fslrcv) on the processor. The code is attached. I 
> am having trouble to get fslrcv working properly. Basically it does not 
> terminate after completing the transfer. However I suspect the root 
> cause is in the driver instead. It is not obvious to me how fsl_read() 
> can tell when to quit hence causing the problem. Do you have suggestion 
> how to fix this?

You have correctly identified the problem - how can the receiving FSL 
driver correctly identify and end-of-file condition at the originator?

One way might be to use the FSL control bit, but will require clever 
driver tweaking.  The write() method will need to know somehow when the 
file descriptor has been closed, and send the last data with control bit 
set.  In this sense the device driver is more like a linux pipe than a 
proper character device.

On the receive side, when a control bit is detected, it signifies EOF to 
the reader after the final word is read out.  Not easy to implement 
actually because there are a lot of subtleties, and it also introduces 
protocol to the driver, which previously just worried about the low 
level transport issues.

A simpler idea would be to tweak fslcat / fslrcv so interpret the first 
two words as a length token.  Problem there is of course that fslcat may 
not know in advance how long its input is (if it's coming from stdin 
rather than a file).

Some ideas to play with.

Cheers,

John
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