[Info-vax] VMS device drivers

[Single Stage to Orbit]

On Tue, 2023-09-19 at 17:40 +0000, Simon Clubley wrote:
> On 2023-09-18, Single Stage to Orbit <alex.buell at munted.eu> wrote:
> 
> 
> Understanding how a device works is only one part of writing a
> successful device driver, especially on VMS.
> 
> I wrote a VMS device driver once for VMS about 20 years ago just for
> fun, and it was such a painful exercise compared to writing a device
> driver for Linux, that I _never_ did it again. :-)
> 
> [It was back in the days of analogue TV, and I put a WinTV PCI card
> into an AlphaStation and wrote a device driver to pull the teletext
> data stream out of the video signal and display teletext pages on a
> VT emulator. Like I said above, this was just for fun.]
> 
> For one thing, unlike Linux, there is absolutely _no_ kernel module
> support in VMS. On VMS, when you need to reload your device driver
> while trying to get things to work, you need to reboot your system
> _every_ _single_ _time_ you want to load an updated device driver. :-
> ( :-(
> 
> Also, unless things have changed in recent years, the only example
> device driver provided is LRDRIVER, which doesn't even begin to
> address a wide range of more advanced topics. On Linux, if you want
> to understand some complex or subtle device driver concept, you can
> just pick a device driver that uses this concept and study how that
> device driver did it.
> 
> Oh, and don't even _think_ about trying to write your own filesystem
> driver for VMS unless you are willing to purchase the VMS source code
> kit, as there's absolutely no public documentation on that.
> 
> On Linux however, the VFS infrastructure is beautifully elegant:
> 
> https://docs.kernel.org/filesystems/vfs.html
> 
> Wish you could do _that_ on VMS.
> 
> > Hopefully VSI has documentation on implementing drivers in x86_64
> > on their website, I would definitely take a look. 
> 
> I doubt it.
> 
> When sanity prevailed, and DEC allowed you to write VMS device
> drivers in C, it became its own book that you had to purchase. That
> was for Alpha, and I never saw anything for Itanium, and IIRC, it's
> been mentioned that there will not be a device driver book for x86-64
> as well.

Thanks for that, that's good to know. Who knows, I might enjoy the
challenge. And anyway, it is much _easier_ nowadays running these
things inside a VM, for development.
-- 
Tactical Nuclear Kittens