This 1/sqrt(x) implementation is a 12 bits fixed point implementation
and a bit faster than a 32 bits divide (it takes about 11% less time
to complete) and could be even faster if one requires only 8 bits.
Also, precision starts getting poor for big values of n which are
likely to be required by small acceleration values.
Implementation by Roland Brochard <zuzuf86@gmail.com>.
Note: If you wonder how code doing multiplications can be faster than
code doing just shifts and increments: I've measured it. One million
square roots in 30 seconds with the new code instead of 220 seconds
with the old code on a Gen7 20 MHz. That's just 30 microseconds or
600 CPU cycles per root.
Code used for the measurement (by a stopwatch) in mendel.c:
...
*include "dda_maths.h"
*include "delay.h"
int main (void)
{
uint32_t i, j;
serial_init();
sei();
serial_writestr_P(PSTR("start\n"));
for (i = 0; i < 1000000; i++) {
j = int_sqrt(i);
}
serial_writestr_P(PSTR("done\n"));
delay_ms(20);
cli();
init();
...
--Traumflug
Before, endstops were checked on every step, wasting precious time.
Checking them 500 times a second should be more than sufficient.
Additionally, an endstop stop now properly decelerates the movement.
This is one important step towards handling accidental endstop hits
gracefully, as it avoids step losses in such situations.
As a sample application, use it in queue_empty().
There's also ATOMIC_BLOCK() coming with avr-libc, but this requires
a C99 compiler while Arduino IDE insists on running avr-gcc in C89 mode.
Teacup handles motor on/off automatically and if your
intention is to stop the printer, M0 is appropriate (and
conforming with the NIST G-code standard).
That said, M84 is kept as a synonym for M2 to enhance compatibility
with slic3rs default end-G-code.
This means, modify existing code to let the lookahead algorithms
do their work. It also means to remove some unused code in
dda_lookahead.c and reordering some code to make it work with
LOOKAHEAD undefined.
We have now Makefile-AVR - AVR specific stuff - and
Makefile-common - common build instructions.
This effort is the begin of preparing Teacup for ARM targets.
To build the target, copy or link Makefile-AVR or Makefile-ARM
(depending on your target) to Makefile.
Powering on even with a heater set to zero doesn't work, as
temperature driven heaters are set to zero all the time. So,
the PSU was running all the time.
The bug was introduced with 569e3d504aafd1ffc8b279b5d7092970cef72287
The requirement was simply neither obvious nor intuitive. Drawback
is, the indices of temperature sensors can now differ from these
of the heaters. That's easier to recognize for newbies, though.
Markus Hitter
Roland Brochard
David Forrest