Hmm. This was asked over on AVRFreaks, and it's FREQUENTLY a Frequently asked question about CPUs/etc, though I don't recall ever seeing it asked here. Since I actually did the experiment, I'll post the answer anyway!
on the same board runs at 2.667MHz. (This does produce the minimal sbi/cbi/rjmp loop that you'd expect, BTW.)
(so that's about a 20x penalty for the arduino library code; sounds about right: the overhead of abstracting IO to "pin number" is pretty substantial: a subroutine call, lookup table to get the port, another lookup table to get the bit, a third to check whether analogWrite is in use, and then less efficient instructions to access the port "indirectly")
Mega Download Speed Limit
Download Zip 🔥 https://fancli.com/2yGcCZ 🔥
Two, the "function" that turns off those timers has a really ugly chain of if/if/if/if statements that should really be a switch or at least if/else if/else if/else statements. I did a timing analysis like you, westfw, and found that the gcc compiler really does optimize the code the same way since it's all forced inline, and comparing against static const data. But it bugs me to see code that relies on the optimizer to rephrase so drastically to do the right thing-- one accidental tweak or compiler update and boom, digitalWrite() could be twice as slow, because the compiler decides to implement what is written, not what might possibly be implied.
re: 2.667MHz example. Was that at 8hz? I have been operating under the assumption that a 16mhz atmega did 16,000,000 instructions per second. Which would be 5.333 million loops per second with only 3 instructions.
I had assumed digitalPinToTimer() would be false if analogWrite wasn't active, but it's actually a ROM-based function that says which timer MIGHT be associated with the pin. Pin3 used in my example IS a PWM output...
The examples are with a 16MHz MDC Bare Bones Board, as shown by the little frequency readout on my Tek TDS210 scope; you're right that that's not what I'd expect based on instruction timings. This may require more investigation!
Are changing fuses allowed :D? it seems you can also program the CKOUT fuse and get the system clock echoed on CLK0 (digital 8), which could be useful I recon. So that would be a 16mhz toggle speed, and it is conceivable that you could control it with an external gate with high precision.
You can usually suck the system clock off of one of the oscillator pins (XTAL2 is an output of an inverter-based circuit.), especially if you're willing to add a gate to square things off. I guess it depends on whether the fuse bits are set for the "low power" oscillator or the "full swing" oscillator. See Sections 7.2 through 7.4 of the Atmega168 data sheet.
In theory you can beat this by filling the memory space with that OUT instruction, and letting the program-counter roll-over at the end of flash, but there are problems with this solution, despite a theoretical 8Mhz output...
in the arduino standard sketch and I come up with one cycle each instruction. Of course, in that case the iteration overhead consumes 6 extra-cycles whatever inside the loop hence a total of 8 cycles.
I mean, it may SOUND awful that a digitalWrite loop is 20x slower than the "fastest possible" loop, but that "fastest" possible pin change operation is a single instruction, which means that digitalWrite is only using on the order of 20 instructions (including function call overhead), and there is not a lot of room for improvement while maintaining the same functionality (there is room for some, but then you hit the fact that people wanting ultimate speed still won't be happy, and blinding speed is not particularly one of the goals of the arduino environment anyway.) (I think digitalWrite got slower in Arduino15, too...)
@selfonlypath: read the whole thread. The cbi/sbi instructions are two cycles according to the datasheet. The extra instruction you removed to make things faster was added to make the output a square wave rather than asymetric.
or 11 cycles for the whole loop by "analysis." How are you measuring 8 cycles?
Note that your code has the pin set to 1 for 1 or two cycles and set to zero for 9 or 10 cycles; I hope you didn't expect a square wave...
sbi and cbi are 2 cycle instructions, according to my Mega88 datasheet.
This should therefore give a loop of 2 ticks ON, 6 ticks OFF, so 2Mhz output at 25% duty cycle.
I'd test this output, but the only test equipment I own is an ohmmeter, an LED and a damp finger (none of which help here).
An extruder velocity limit would be sufficient in case. As the maximum velocity could be calculated by the maximum mm/s and nozzle width. I can change it for retraction. But the only thing I find is extrude_only_velocity what not does what I want as far I understand.
Not sure I completely understand your intention: Are you looking at implementing a maximum volumetric flow for each material and would like Klipper to respect these values and tune down speed if exceeded?
And of course you are right. But my profiles supports the most important features that should be changed if the material is changed. I think this is last one I really need to address. If this is done no reslicing for other materials are necessary any longer.
Maybe it will not reach the same quality as reslicing would do, but quit close to it. The slices do not do that much magic. (maybe this is depending on the material in some cases)
Uhh this is a nice idea for a hack It could be possible to set the nozzle diameter mega small too have this limits. At least if the monitoring will lower the speed instead of exit with an error.
Can you point out the source code file, so I can read how it is implemented?
Thanks for your help, I could solve the issue by implement the missing functionality directly into klipper. It was really important to know and understand the current state. So your answer was really helpfully as they are often!
For all that searching for a solution, here it is, but I really hope that the pull request will be accepted, so it possibly to contribute more code depending on it without having a custom version of Klipper:
Hello good afternoon!
I am before the update of 2019.12.20 I used raidrive directly with mega had transfer speeds of up to 12mb / s I updated to the current and my transfer rate dropped to 651kbps does not go out of this speed, I would like help as it is dissatisfied with this update.
Hello good afternoon!
I understand perfectly well that Mega has a traffic limit, but my account has no limit currently working with a business account, Business - MEGA this account has no traffic limit, I still have slow transfer speeds to the business account. , my speed for mega is between 650kbps with maximum speed of 1.2mb, on other servers I have extremely high speeds with raidrive.
If you have the "Printer Settings" plugin loaded (it can be found in the MarketPlace) then you can change those settings in Cura and that will affect when the other "speed" boxes turn orange or red. An orange box indicates that the number you entered is getting close to the max or min for that setting. If the box is red then you have entered an illegal value for the setting and Cura often will not slice if there is an illegal setting.
As you can see, I have altered the max Z speed and maximum E speed IN THE PRINTER. So you can change the printer settings in Cura but it will effect Cura only (I did that to match the new values in my printer). To modify the settings in the printer you would need to send M203 E??? and then M500 to save the new setting. Some printers allow a user to change the Max Feedrates, Max Accel, and Max Jerk via an LCD menu.
As I tried to explain - that only affects Cura settings. The printer is separate and may have a different value for Maximum E Speed. There is no way for Cura to know what the printer setting might be unless you check the printer and then manually update the "Printer Settings / Maximum Feedrate" to match. In a perfect world, the max in the printer is also 40 but that isn't necessarily true.
If the printer has in it's memory (in M203) that the Maximum E speed is "10" then whatever you enter in Cura is thrown out the window when the printer receives a gcode command that asks it to go faster. The printer will override the Gcode and although you may have entered "40" in Cura the printer will calculate it's moves at 10mm/sec for the Extruder. That is why you should match the "Maximum Feedrate" in Cura to what your printer has in M203. 152ee80cbc