I've managed to get IRIX 6.5.22 on Indy R4600 installed under MAME 210 and running under MAME 212 ...
I had to install using 210 because on my PC (i8700k Win10) both 211 and 212 at the moment do not appear to correctly map the CDROM to SCSI(6), and the PROM thinks it's a 'disk' instead of 'cdrom' (see hinv output).
This is the command line being used for this shot (I excluded -cdrom1 option to avoid any possible hangups but the hinv output is the same with or without -cdrom1):
I have allocated a 36GB HDD and it's running 24-bit graphics.
I have done a full install of IRIX 6.5 (including Freeware and SoftWindows95) and then did a full upgrade (not yet included any extras, just IRIX) to 6.5.22.
It was quite tedious because in MAME 210, the mouse was slow and jerky and then, the left-mouse button did not work however, whenever the mouse moved along the X-axis from left-to-right, a left-button-click event would fire and sometimes hold and this would happen randomly. So, if I wanted to click on a button in a window, I would first need to move the mouse right-to-left to position it just to the left of the button that I wanted to press then, I would slowly drag the mouse left-to-right horizontally and it would magically press the button for me as I dragged the cursor across it ... I installed 6.5.22 under those conditions and it's taken a long time, not to mention the thirty-or-so times that MAME would randomly lock up part way through the install (which in itself took just over 4 hours to complete!).
I will see if I can talk to the MAMEDEV guys about those issues but suffice to say, MAME Indy R4600-133 (Indy_4613) works with Irix 6.5.22!
P.S. Big Thanks goes out to all the devs who have made this possible! Thanks heaps!