kens

55 ms·

961.
by kens 4y ago
I'm pretty sure that the extra bit will get ignored. There is internal circuitry that expands the register number in the instruction to a 5-bit register number. (You need 5 bits to handle 8-bit registers, 16-bit registers, segment regi
962.
by kens 4y ago
Author here. Any questions about 8086 microcode?
963.
by kens 4y ago
Unicode has completely separate rules for characters and emojis. Characters and scripts generally need solid documentation that they are real existing symbols. Emojis, on the other hand, are accepted largely on how likely they are to be use
964.
by kens 4y ago
Looking at the 8086 in detail has given me much more appreciation for RISC. Every special case in the 8086 or random footnote corresponds to a block of extra logic. And there are a lot of them.
965.
by kens 4y ago
Author here: this is about as far as I can go. When chips get more than 1 metal layer, I don't have a good way to examine them. Professional reverse-engineering firms can go a lot further.
966.
by kens 4y ago
Yes, more 8086 reverse engineering. I'm here for questions...
967.
by kens 4y ago
I'm pretty sure that steering wheel locks were required by law starting in the 1970s. Does this process bypass the steering wheel lock somehow? Or do these cars not have steering wheel locks?
968.
by kens 4y ago
For those who don't like Twitter threads, this is also in blog form: https://www.righto.com/2023/02/bendix-central-air-data-compu...
969.
by kens 4y ago
I'm here for all your mechanical computer questions :-) This article is a bit of a change of pace from my 8086 posts.
970.
by kens 4y ago
The INC/DEC instructions block the control signal that updates the carry flag. This happens in the carry flag circuit.(See footnote 10.) For LOOP, the microcode doesn't have the F bit set, so the flags aren't updated from the
971.
by kens 4y ago
That chip is too complex for me. My cutoff is chips with one metal layer. I don't have a good process for removing one layer at a time if there are multiple metal layers. Also, Moore's law means that chips get exponentially more c
972.
by kens 4y ago
> please do a blog post on the insane bus management on this device I'm working on it, but it's a difficult topic. The bus management circuitry is both very complicated (a bunch of flip flops making a complex state machine full
973.
by kens 4y ago
Yes, there's an output from the Group Decode ROM that indicates the instruction is an IN or OUT instruction. This causes the M/IO line to signal an I/O operation rather than a memory operation.
974.
by kens 4y ago
The 8086 inherited the separate I/O space from the Datapoint 2200, a "programmable terminal". Since the Datapoint 2200 had a custom TTL processor, it was convenient to build in instructions to manipulate its I/O hardware
975.
by kens 4y ago
More 8086 reverse-engineering for your enjoyment. Let me know if you have any questions.
976.
by kens 4y ago
Forced Windows updates caused me no end of problems too. I'd run a simulation overnight and discover Windows had rebooted on its own and I lost all my results. Or I wanted to show a movie at a birthday party but Windows decided it had
977.
by kens 4y ago
Inside Google, there was this weird semi-status-symbol thing where headshots had a colored gradient directory if you were an "important" person and a plain background for most people. Anyone know if this is still at thing at Googl
978.
by kens 4y ago
The Bitcoin symbol is the most well known. Also the Group Mark from 1960s mainframes. The mask work symbol, like copyright for IC dies. And four half-stars.
979.
by kens 4y ago
This article is sort of a prelude to looking at the 8086's hardware. (I was looking at the Intel documentation and realized it was confusing and slightly wrong, so needed to figure out what is really happening.) The 8086 implements the
980.
by kens 4y ago
IBM System/360 (1964) had separate instructions for decimal arithmetic. The Z80 had a DAA instruction, but a separate status bit tracked if the previous operation was addition or subtraction.
981.
by kens 4y ago
If there's something missing from Unicode, you can propose it and there's a good chance they will add it to Unicode. Source: I got 7 characters added to Unicode.
982.
by kens 4y ago
No. It's often believed that the 8008 came from the 4004, but they have completely different architectures. They are essentially unrelated except many of the same people worked on both. The 8008 came from the Datapoint 2200, a desktop
983.
by kens 4y ago
The algorithm was published by Dennis Allison in "A design philosophy for microcomputer architectures", Computer (Volume: 10, Issue: 2, February 1977), https://doi.org/10.1109/C-M.1977.217645 Curiously, the a
984.
by kens 4y ago
There's not a lot to say about the ASCII adjust instructions. I mention them in footnote 2. They are the same idea except they act on a single BCD digit. They aren't specifically for ASCII, but if you ignore the upper nybble, ASCI
985.
by kens 4y ago
Yes, the other adjust instructions are invalid in 64-bit mode. The Auxiliary Flag can get set in 64-bit mode, but I don't think anything uses it. You could access it through the EFLAGS register but I think it's otherwise useless.
986.
by kens 4y ago
Anyone have questions on the DAA instruction? This is a bit of a niche post, I have to admit.
987.
by kens 4y ago
Wow, that video is exactly my thoughts, but expressed much better!
988.
by kens 4y ago
I took a 20% pay cut for a 4 day/32 hour work week a few years ago and it was great. One additional day off is much more free time than you'd think. It's 50% more days off compared to the weekend. I'd recommend it to any
989.
by kens 4y ago
I don't have the solution; I just see the problem :-) Programs could be in some sort of database rather than a set of files, so the code you're interested in gets displayed without you caring about how it is broken down into a seq
990.
by kens 4y ago
My unpopular opinion is that computing is stuck in a local maximum based on technology from the 1970s. In particular, typing into an 80x25 terminal window with unformatted fixed-width characters should be obsolete; we don't need compat

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