Objective Development Forums

Re: Minimal USB implementation

2014-03-19T22:31:12+02:00

Some write up for those interested:

http://cpldcpu.wordpress.com/2014/03/19 ... attiny-10/

Statistics: Posted by cpldcpu — Wed Mar 19, 2014 10:31 pm

Re: Minimal USB implementation

2014-01-22T17:51:40+02:00

That looks like something that would break arbitrarily with new compiler versions

Statistics: Posted by cpldcpu — Wed Jan 22, 2014 5:51 pm

Re: Minimal USB implementation

2014-01-22T02:53:21+02:00

At least with avr-gcc 4.5.3, I think I was able to silence the optimizer warnings by initializing a variable with itself, e.g.char c = c;. Too bad there are so many snags to inlining assembly, as otherwise it could be possible to get more optimal code by using just C rather than mixing it with assembly.

Statistics: Posted by blargg — Wed Jan 22, 2014 2:53 am

Re: Minimal USB implementation

2014-01-21T09:52:06+02:00

Whenever I tried that, the compiler would also initialize the variables, which took up more space than it saved.

Statistics: Posted by cpldcpu — Tue Jan 21, 2014 9:52 am

Re: Minimal USB implementation

2014-01-20T02:44:05+02:00

Can you just set them as out variables? That would force the compiler to give them registers and let it know that you're modifying them.

Statistics: Posted by blargg — Mon Jan 20, 2014 2:44 am

Re: Minimal USB implementation

2014-01-19T17:14:19+02:00

blargg wrote:Actually not so much call overhead, but richer information to the optimizer about exactly what registers are modified. It could probably also be written to let the compiler assign all the registers it uses.

I wish I have not found a way to define variables in the assemblercode without having the compiler initialize them.

Statistics: Posted by cpldcpu — Sun Jan 19, 2014 5:14 pm

Re: Minimal USB implementation

2014-01-19T07:55:06+02:00

Actually not so much call overhead, but richer information to the optimizer about exactly what registers are modified. It could probably also be written to let the compiler assign all the registers it uses.

Statistics: Posted by blargg — Sun Jan 19, 2014 7:55 am

Re: Minimal USB implementation

2014-01-19T04:30:55+02:00

You mean call overhead, I see!

Statistics: Posted by stf92 — Sun Jan 19, 2014 4:30 am

Re: Minimal USB implementation

2014-01-18T12:59:48+02:00

That is where it is right now. The idea was that inlining saves code space.

Statistics: Posted by cpldcpu — Sat Jan 18, 2014 12:59 pm

Re: Minimal USB implementation

2014-01-18T12:44:22+02:00

Why don't you include the CRC routine in usbdrvasm.S. Christian Starkjohann did this in his first implementations. That way the compiler will have nothing to do with it and code will be minimal.

Statistics: Posted by stf92 — Sat Jan 18, 2014 12:44 pm