[2.0.x] Fix extruder stops extruding with LA

[Sebastianv650]

Fixes #11711 and #9899.

When the advance ISR rate of the current block is identical to the advance ISR rate of the previous block and the current block has no acceleration phase the advance ISR will not be started as it should. The esteps during the cruising phase will then not trigger the advance ISR any longer due to:

if (LA_steps && LA_isr_rate != current_block->advance_speed) nextAdvanceISR = 0;

The assumption was that each block enters the acceleration planning block at least once so the extruder ISR gets started. As this is false, I now initialise the extruder ISR when the new block is set up. On the other side, we can now remove some code lines as LA_isr_rate is always started in a defined state at the beginning of the block.

I tested the change with @Itox001 configuration which is known to cause the issue and it solves it. Also K=0 and my own configuration was tested.

Calling @Itox001, @buchnoun and @SJ-Innovation please give this PR a try before it gets merged. I had a ton of problems with the quite buggy Arduino 1.9 beta which I used for the 2.0.x code and it's quite late now, don't want to get a buggy fix merged due to fatigue!

[me-honest]

Tested, and have not noticed any strange with it.

[ModMike]

I'm using an Ender 3 controlled by an Azteeg X5 Mini Wifi with TMC2224 (TMC2208) drivers.

Whenever I enable LA and set to 0, the extruder will not work. So far I only tried the pattern generator code files.

Any tips?

[ModMike]

Just thought of something, would junction deviation cause any issues?

[thinkyhead]

We've been over it and I believe we resolved all issues of JD interaction with LA.
See if an issue search turns up the relevant threads.

[Sebastianv650]

I'm using JD together with LA all the time, no issues. As you found out already, this is a stealth chop issue.