HPRT N41 print issues on Greyscale

[ikaruswill]

Hi there, 👋 I just got a HPRT N41 which is essentially identical to the SL42. I compared the PPDs and they were the same except that the color options were not commented out (None/Greyscale) among other paper size option differences (SL42 has more paper size options).

diff N41.tspl.ppd sl42.tspl.ppd ignoring paper size additional options:

96,101c210,215
< *OpenUI *ColorOption/ColorOption: PickOne
< *OrderDependency: 310 AnySetup *ColorOption
< *DefaultColorOption: GrayScale
< *ColorOption None/None:			"<</HWResolution[203 203]/cupsBitsPerColor 8/cupsColorSpace 3>>setpagedevice"
< *ColorOption GrayScale/GrayScale:	"<</HWResolution[203 203]/cupsBitsPerColor 1/cupsRowCount 8/cupsRowFeed 0/cupsRowStep 0/cupsColorSpace 3>>setpagedevice"
< *CloseUI: *ColorOption
---
> *%OpenUI *ColorOption/ColorOption: PickOne
> *%OrderDependency: 310 AnySetup *ColorOption
> *%DefaultColorOption: None
> *%ColorOption None/None:			"<</HWResolution[203 203]/cupsBitsPerColor 8/cupsColorSpace 3>>setpagedevice"
> *%ColorOption GrayScale/GrayScale:	"<</HWResolution[203 203]/cupsBitsPerColor 1/cupsRowCount 8/cupsRowFeed 0/cupsRowStep 0/cupsColorSpace 3>>setpagedevice"
> *%CloseUI: *ColorOption

If I printed in Greyscale (Default) the printer would print a bunch of lines with diagonal patterns, advance several mm, and then stop printing as though it's complete. No errors are observed in the error_log except for some persistent /var/spool/cups/d00130-001 (object 23 0): object has offset 0 lines which is probably not related.

But if I printed with the Color option of None, it will work just fine, prints the whole document except the colored parts of my print wouldn't show up. Probably because it's now Black and White but the color didn't make the threshold.

I'm pretty sure it's mainly an issue with the filter as direct USB works for at least MacOS using the PPD and manufacturer filter.

Some extra details:

• cups 2.3.3op2
• Raspberry Pi OS Bullseye (armv7)
• Raspberry Pi Zero 2W
• Using the cups 2.2.0 armv7 filter from this repo

Does this filter support the Greyscale color option in the PPD? If not how should I print in Greyscale? Or am I missing something somewhere? Would appreciate any advice, thanks!