[Linux-parport] hardware ECP reads

Malcolm Blaney malcolm.blaney at maptek.com.au
Wed Dec 14 19:03:03 EST 2005

Hi Mike,

You're right that the kernel can't do full-speed ECP reads. That doesn't 
mean you can't read from an ECP enabled parallel port though, since I'm 
  pretty sure it drops back to a compatible mode and the bandwidth you 
get is just less.

The company I work for has modified the parport_pc driver for a 2.4.18 
kernel to make full use of ECP though, so if your interested in working 
on the driver I might be able to pass on the code. Most of it is already 
there as it's very similar to the ECP write code which does what you want.


Mike Caplinger wrote:
> After going through the process of recompiling the parport driver to
> use ECP, I've discovered that seemingly even with all of the options
> enabled (CONFIG_PARPORT_PC_FIFO, CONFIG_PARPORT_1284), ECP reads still
> always go through the software emulation function in
> parport_ieee1284_ecp_read_data, and are very very slow.
> The key seems to be the fact that parport_pc_ecp_read_block_pio is
> never called by the driver, as indicated by the comment "currently
> broken, but working on it.. (FB)".
> I'm doing the tests on RH 9 (kernel 2.4.20-8) but the code in the
> latest 2.6 stable release ( appears to be the same.
> Is this true, or am I confused?  Is the driver unable to do ECP
> hardware reads?  If true it's unfortunate, since I was so looking to
> be able to migrate all of my DOS ECP-reading applications over to
> Linux.  One would be better off mapping the I/O ports and writing them
> directly, making the parport driver fairly useless.
>         thanks,
>         Mike Caplinger, Malin Space Science Systems
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