Topic: IShow DAC hack attack

[Fanny Pack]

PS James, in order to access the IShow DAC via Windows I have to open it as a file.  In fact, all system device drivers are accessed as files.  Does that give you a warm fuzzy feeling?

[Fanny Pack]

Where is everyone?  I am so excited an no one is here to talk to.  Maybe it isn't good to have 3 espressos before 7am.

[mikkojay]

Hi Gary,
  Good job!  That's pretty cool.  Hey, this is my first post here- I have just read here and there so far.  Spaghetti will be a great option for people who buy these dacs.  Have you figured out what it would take to talk to more than one of these simultaneously? 
  These might make nice, cheap dacs for satellite beam projectors for use in conjunction with the soundcard/other as the "main" graphics dac.
Have a good one,
Mike

[Fanny Pack]

You should be able to use more than one of them at a time unless there is something I don't know about.  I only have one so I have no way of testing, but I don't see any issues from a software point of view.

[James]

PS James, in order to access the IShow DAC via Windows I have to open it as a file.  In fact, all system device drivers are accessed as files.  Does that give you a warm fuzzy feeling?

So is it a named pipe or what?

James. 

[Fanny Pack]

James, not sure what it is. You get a file handle after you create the file and then you send IOCTLs to it with data. You can write and read that way.  It works.

It took a bunch of trial and error but I finally got the IShow DAC working well with Spaghetti.  I can play shows with it now with Spaghetti.  The quality is alright.  It has some hot spots that aren't there on my other DACs and I think the speed maxes out well below 30K.  I'm going to put a scope on it soon and see how fast it goes. I'll do a bit more tweaking on it but otherwise it is a done deal.  I played the shows that came with it using the iShow software and also using Spaghetti and Spaghetti plays them back a LOT better.  There are all kinds of dashed lines and stuff that shouldn't be there when they are played with the iShow software.  No wonder people don't like it.  It isn't suited for detailed graphics shows but for more simple content it will do.  It's a nice fit for people who only have 15K scanners I guess. 

Next I might study the board and see if I can't figure out how how well it should perform in theory.  It's possible that I could rewrite the firmware... don't know yet.

So, now we need to order an FB3 and get it working with LaserBoy.  I'd love to see that demoed to Bill Brannon at the next SELEM.

[James]

That's really weird!

That is EXACTLY how it works in Linux.

The kernel side of the driver makes a fake file appear in the /dev/ directory when the kernel boots up. From C, you open it for binary read and write and you set stuff in the driver (any driver) via a call to ioctl(...) that takes the open file descriptor as an argument, a pointer to void for whatever data exchange you need to do and an int to tell the driver what you want to do. The kernel side of the driver just switches on the int instruction and calls the appropriate function with the pointer to data you provided. All the structures and stuff you might need are in the device driver header file that comes with the Linux kernel.

So, now we need to order an FB3 and get it working with LaserBoy.  I'd love to see that demoed to Bill Brannon at the next SELEM.

You're a very sick man, Gary. 

James. 

[Fanny Pack]

The kernel side of the driver makes a fake file appear in the /dev/ directory when the kernel boots up. From C, you open it for binary read and write and you set stuff in the driver (any driver) via a call to ioctl(...) that takes the open file descriptor as an argument, a pointer to void for whatever data exchange you need to do and an int to tell the driver what you want to do. The kernel side of the driver just switches on the int instruction and calls the appropriate function with the pointer to data you provided. All the structures and stuff you might need are in the device driver header file that comes with the Linux kernel.

Yep, that is exactly the same way that it works in Windows.
http://msdn.microsoft.com/en-us/library/aa363216(VS.85).aspx

[meandean]

  Well, I guess Jimmy wasn't full of hot air after all on this one!
Congrats on your DAC hack!

[Fanny Pack]

  Well, I guess Jimmy wasn't full of hot air after all on this one!
Congrats on your DAC hack!

[James]

You say that like I am normally "full of hot air".

What's up with that?

Don't you know me well enough to know that if I say anything it's because I know what I'm talking about?

James. 

[Fanny Pack]

The whole "file" thing really isn't a file at all.  It's just a filename that gets you a reference to something that you can issue commands to.  It isn't stream or pipe like a traditional file is.  I have dealt with serial ports that are accessed like files, though.  But still, there is a heck of a lot of code that is specific to the device that gets exercised when you make calls to it.   That was my point awhile back.  I can't plug in my iShow DAC and have it magically appear as a file.  There are device drivers that have to be installed, etc, etc. 

[meandean]

Don't you know me well enough to know that if I say anything it's because I know what I'm talking about?

  You have no sense of humor...

[James]

I think I get it.

You don't always deal with devices in Linux as files either. With a sound card, you do. You actually read or write with standard C file IO, but not with the video card. With that, you open the file and immediately mmap memory-map it to a pointer and the display ram gets hooked up to your code right there.

But ioctl() calls are made in both cases to set or get things in the driver.

James. 

PS. I guess I'm still dazed that you don't get the Format 3 nonsense. 

[Fanny Pack]

Format 3?  What's that?