[Linux-parport] Parport signals stability with SiS chipset

[Eric BENARD / Free]

Hi !

I'm trying to get a small jtag software to run under Linux and I meet problems 
with the parallel port :
- on two PC (a Dell Intel based Notebook and an Asus VIA/AMD based), 
everything is ok, I can write and read correct data to the board (an ARM7 
cpu)
- on the other PC (Asus Pundit with SiS651/962 chipset & Celeron4 CPU), the 
parport IO are always swinging so data gets corrupted.

Both PC have the same settings (SPP). I tried with 2.4.23 & 2.6.1 & 2.6.2 
kernels on the Asus without any success.

I quickly tested on a SiS630 PC and I have the same problems than on the 
Pundit, so this could come from a problem with the SiS chipset handling 
parport.

Of course, I checked that no other software was trying to use the parport. I 
unloaded lp, and only ppdev is loaded.

The problem is the same if I try to access the parport directly (io @ 0x378) 
or through ppdev (/dev/parport0).

Here is the schematic used for the JTAG adapter : 
http://axl.freeyellow.com/iPAQ/xilinx-DLC5-pp2jtag.pdf

Do you have an idea of what could be wrong ? Or maybe where I should look to 
get more details and solve this problem ?

Many thanks for your help & best regards
Eric