Driving two stepper motors

[tenaja]

Oh, yeah... if your drive only needs a 5uS pulse, you should minimize the delay in the interrupt, or use it to check for a second interrupt. At 40MHz that is 50 instructions minus the call/return, and you could exit early if you were going to handle the other motor stepping.

[Bill Legge]

Tanaja,

Yes, I've seen the embedded.com article by David Austin. There is also a good application note on the ATMEL site (Application note AVR446) that has rampup/down calculation:

Cn = Cn_1 - 2*Cn_1/(4n+1)

In the C language - I have yet to see if PBP is fast enough to do this.

Was the formula you used like the one above or was it the more complicated 'exact' calculation that needs square roots? If it takes 105uS that's in the ball park for my application.

Re 'context saving' - if you mean 'wsave' and so on - I don't think it's necessary on the PIC18F8722?

Regards Bill Legge

[tenaja]

Yes, I've seen the embedded.com article by David Austin. There is also a good application note on the ATMEL site (Application note AVR446) that has rampup/down calculation:
Cn = Cn_1 - 2*Cn_1/(4n+1)

In the C language - I have yet to see if PBP is fast enough to do this.

Was the formula you used like the one above or was it the more complicated 'exact' calculation that needs square roots? If it takes 105uS that's in the ball park for my application.

1. The concept that Basic is slow and C is fast is a remnant of the 70's when there were no basic compilers, just interpreters. Although it has bee nreduced to a myth that won't let go, in reality it is now all about which compiler author wrote efficient code--not which language he wrote. Recently someone posted that PBP compiled some code in 460 words, but MikroB wouldn't even fit in the chip. My guess would be that the MikroC would be just as bad, unless they had two compiler authors and one was a lousy coder. BTW, in short code, PBP and Proton are similar... but when it gets long, or you use a mix of Words and Longs, Proton really shines. (And when using interrupts.)
2. That's the article and formula I was talking about. without much tweaking, it was running at the speed I previously quoted. It takes around 400 instructions to do a 32 bit sqrrt on a PIC... only good for buffered or slow moves.

Re 'context saving' - if you mean 'wsave' and so on - I don't think it's necessary on the PIC18F8722?

The 18F does save the wreg if you use the Fast Return, but not the variables you are changing and the registers related to them. For instance, if you are in the middle of changing an array value and an interrupt occurs, and you access an array (any array) in the interrupt, you have to save the INDF & FSR registers and anything else PBP uses to manipulate arrays. Proton has this built in, and many PBP users have used the DT Instant Interrupts... which is kind of an oxymoron since all of the saving removes the instant part.