[Feature or Bug] Behaviour of M204

[timschneider]

Setting the max acceleration via M201 is limited to values not zero or negativ.
The following will result in an acceleration of 0.1.

M201 X0

M201
Accelerations (mm/sec^2): X: 0.1, Y: 1500.0, Z: 70.0, E: 3500.0

I guess it is a kind of safeguard, so that the printer can move, even if the acceleration is low.

M204 behaves differently

M204 P0 T0

M204
Maximum printing acceleration 0.0, maximum travel acceleration 0.0 mm/sec^2

This stops the printer from moving the axis while still updating the new position, e.g.

G90
G1 X100 F3000
G1 X500 F3000

will let RRF think the head is at X500 even if the axis didn't move at all and btw. the moves are executed immediately.

It is also possible to set the values negative.

M204 P-1 T-1
M204
Maximum printing acceleration -1.0, maximum travel acceleration -1.0 mm/sec^2

This is just an observation I made when I noticed some strange behaviour from the printer.

SBC Mode

M115
FIRMWARE_NAME: RepRapFirmware for Duet 3 MB6HC FIRMWARE_VERSION: 3.5.0-rc.2 ELECTRONICS: Duet 3 MB6HC v1.02 or later FIRMWARE_DATE: 2023-12-14 10:32:22

[dc42]

@timschneider you are correct, RRF does not currently check that the parameters to M204 have sensible values.

[timschneider]

@dc42
Thank you for adding the same checks as in M201 to M204 and the fast response!

btw. would you prefer to get forum posts/bug reports or PRs for these small things?

[dc42]

@timschneider said in [Feature or Bug] Behaviour of M204:

@dc42
Thank you for adding the same checks as in M201 to M204 and the fast response!

btw. would you prefer to get forum posts/bug reports or PRs for these small things?

If the fix is simple and obvious (e.g. a typo in a text string) then a PR is fine. If it's not completely clear what the fix should be or there are multiple ways of achieving it, then I would prefer a forum post.