#perq — Public Fediverse posts

In classic spend-an-hour-to-save-five-minutes efficiency, I'm hand-coding 48-bit horizontal microcode... in octal!

(and sometimes the bits are inverted!)

   20  7020  25  10 6 1 1 0  1 2  2 356  0  3    -  SetDDS: R21 := 10, StackReset, loc(7020);  ! Increment display
  ! X : ALU dest register is R25
  ! Y : Y source is the lower eight bits of a constant (8) (not a long constant load? so upper bits 0)
  ! A : AMUX input is the X register
  ! B : BMUX input is a constant value
  ! W : ALU output IS written to any register
  ! H : DMA requests are enabled (seems used only in special cases)
  ! AL: ALU function is identity(BMUX)
  ! F : Combines with SF=2 to mean StackReset
  ! SF: Combines with F∈{0,2} to mean StackReset (does which matter in some other way?)
  ! Z : Probably fills JMUX<7> thru JMUX<0> for a short jump (active low!)
  ! CN: Select the "true" condition to pass along to the sequencer
  ! JP: Sequencer should execute a conditional jump
  ! VT: Not a real field: the jump target VA

#PERQ

45 days until #RetroFest 2026 in Swindon. #PERQ status:

• Flaky Z80-based I/O subsystem: sometimes the #Z80 jumps off the tracks and executes nonsense code
• Disk boots fail: the microcode attempts to load blocks far beyond the end of the disk

Trying today: DIY diagnostic microcode

POV: #PERQ hardware debugging, as usual. The #Z80 (serving as an I/O coprocessor) is behaving strangely: fetching instruction bytes without toggling the M1 pin, jumping to random locations at around 47uS after coming out of reset; what's going on here?

@wec good luck, I look forward to any updates about your progress that you share! I do also hope that continued research into the 37T will reveal some way (e.g. by a software emulator) to run EM/YMS someday: as a #PERQ botherer I am so curious about what @d_j_fitzgerald suggested was (something like) IBM's answer to the PERQ.

Developing technique for "disk baking". The box is a filament dryer for 3-D printing, and the disk "bakes" inside at 55 °C for six hours in an attempt to stabilise the degraded binder that holds the magnetic oxide to the PET substrate. This disk is one of several 8" floppies for #PERQ shared with me by another Mastodon person --- thanks! (So far I've mainly recovered floppies you can already find on Bitsavers, but the as-yet-unarchived ones will be tackled soon.)

Meanwhile, the #PERQ has broken once again. A problem somewhere on the EIO board again, affecting floppy and hard drive both, but only after some data have been loaded from them. DDS=157 or 158 on HDD or FDD boots of POS respectively. PERQs gonna PERQ...

Handy: it looks like it works fine to replace a PAL16R8 with a GAL16V8 (at least a GAL16V8D, -15) as the DCD2 chip on a #PERQ 2T2's DIB.

I was able to reuse the old, singed DCD2 label from the original PAL... which I might have plugged in backwards one day...

oera perq
#kamloops #train #graffiti #art
#oera #perq

Just in time for #PERQtober ! An adapter to replace your missing or broken #PERQ T2 landscape monitor with a VGA display. Thanks to @skeezicsb for early advice.

So you want to connect the floppy drive ribbon cable in your #PERQ to a Gotek instead of a Shugart 851 floppy drive? This might be handy...

At last, at last, at last. This boring photo may be one of my biggest milestone posts for this year: RSRE's Flex operating system recovered and finally running on an actual #PERQ 2. With thanks to @skeezicsb of course.

#Smalltalk -80 on #PERQ --- Mario Wolczko's implementation running with maybe some gremlins still to sort out. attn @skeezicsb as usual 🙂

#PERQ PNX 5.03 manual pages. The most interesting ones don't render very well with my hacked copy of a roff-in-JS "typesetter", but some interesting nuggets are there to reward persistence.

Grab your ear defenders, it's time to see the exciting features of 1986's PNX 5.03, the Unix for the #PERQ 2 workstation! Skip to 2:10 to bypass booting and go straight to the non-X11 graphics action!
https://www.youtube.com/watch?v=TZRoDxD0-JE

Here's some floating point code (and yes, I'm aware of the gamma function). It looks like PNX does floating point in microcode. (#PERQ has no dedicated FP hardware, though there is an unpopulated spot for an 8087 on one board.)

#PERQ documentation for cc may not talk about -S, and the assembler may be classified, but cc -S still works just fine. It should not be too hard to figure out more details of the architecture by looking at compiled C code. attn: @skeezicsb

#PERQ PNX seems a bit cagey about its own instruction set! cc(1) lists no -S flag for generating assembly output, but it does mention an assembler. OK, so let's man as:

Here's the manual for the ICL PNX C compiler. PNX, a System III UNIX for #PERQ workstations, uses its own instruction set, which it programs into the PERQ's CPU microcode. But there is a mysterious absence...

I have fresh-install disk images of #PERQ PNX 5.02 and 5.03 for the Gesswein hard drive emulator (emulating a 43 MB Vertex V150 MFM hard drive). Anyone want a copy?

Here are some images from ICL's looping demo that runs on the #PERQ 2T2 under PNX 5.

OK, so the #PERQ 2T2's disk system will work if:

• you let it warm up for a bit
• you have the logic analyser attached to U9 on the EIO board
• ...and running

attn @skeezicsb , @fvzappa

About a month ago I fixed the mouse on my circa-1983 #PERQ 2T2 computer: a key feature for an early graphical workstation. It was a wild troubleshooting journey --- in the end, there was nothing wrong with the mouse itself. You might not believe what it was...

Fixing #PERQ computers eats notebooks! It was working, now it won't talk to the hard drive. After probing three interface boards on the bench, I now think the problem lies elsewhere...

U141 on the EIO board is another 74S225 dropping bits, the third failed 225 so far. The 225 has proved to be the most unreliable kind of IC in my #PERQ 2T2, and the machine has at least 22 of them.

I've recruited my #rc2014 Zed Pro Pride's Z80 SIO/2 serial port interface IC into #PERQ service: the PERQ has two and at least one was broken! @rc2014 , I will have to collect your top tips this weekend for getting spares!

@andreas_heitmann @smittytone I sincerely hope you’re not taking me for an #Apple fanboy. I am not. I just happen to be using #UNIX-like OSs ever since 1984 (the first one being #PNX on an #ICL #Perq — Learn all about this one on Wikipedia. This includes #NetBSD and assorted #Linux based sytems. I just believe one has to be flexible enough not to bet fixated on a particular feature perhaps better handled by another system. Apple isn’t doing badly at all.

Let’s continue once again our magical trip into GUI Wonderland, and leave timesharing behind with the extremely capable Three Rivers / ICL PERQ and its stunning graphical capabilities! If you want to come with us, feel free to check this article out!

Anche in 🇮🇹

https://blisscast.wordpress.com/2024/08/20/three-rivers-perq-gui-wonderland-4

#perq #vintagecomputer #retrocomputer #GUIWonderland