Posts by AddieM 8 publicly visible posts • joined 2 Sep 2020
*Hopefully* it's only a feature available to those that hand over the dosh. Because if any old program can register itself to read whatever text you've got highlighted and run some arbitrary code to decide whether to offer an action or not, then that's your entire clipboard history being sent off to some server somewhere for perusal, while masquerading as something else.
Or alternatively, just switch the damned thing off.
It's convenient for the character generation that the bottom five bits of the low order byte represent the screen from left-to-right, and the bottom three bits of the high-order byte represent the 'three chunks' from top to bottom. It means that when you're copying character glyphs that you can set the low-order byte to the 'top' of the character, and iterate when drawing it downwards by incrementing the high byte.
But the missing bit of the puzzle here is getting the image to screen; there's no double-buffering or anything, the ULA just locks the memory that it need to draw the next scanline and reads it simultaneously with the CRT output. The Z80 CPU in the Speccy isn't fast enough to read/write the screen memory as quickly as is needed for video output, so it needs the custom hardware. Memory access to the screen display area is contended; it will take a couple more cycles to change values that the ULA is reading, since it absolutely needs priority. (If you're cunning, you can measure this behaviour to optimise your screen drawing code and minimise flicker.) And it happens that this weird memory layout is just right for outputting PAL video.
On the other hand, since the only screen output is direct writes to the framebuffer, then all Spectrum games have 60 Hz output - no console-style 'cinematic 30 fps' :-)
*Per suite*, which I'm assuming is about thirty machines or so. Keyboards and monitors don't need to be replaced, so that' £(600 to 700) per machine. Seems cheap to me; might be that much to get them in a box on a palette by the front gate, but by the time you've installed and configured them, stuck a PAT label on them, wiped and ejected the old ones, then the man hours add up.
That would probably be enough commands for my personal projects, when it's only me making changes, although I'd probably add `git diff` as well. For work, when my colleagues might inconsiderately change files that I'm working on too, or I need to backport fixes to a release branch, then `git rebase` and `git cherry-pick` are essential too.
Hey Tim. My background is as senior commissioning engineer in the water industry for the last twenty years, working across Europe. Regarding our water companies: I would say that any cynicism in dealing with them is extremely well-deserved and completely justified. On the other hand, I've always found Severn Trent to be relatively open about what they do, and they don't take *every* opportunity to screw over their own staff, contractors and suppliers - I'd probably rate them 2 out of 5 for being water company bastards, there's a lot of them I've really enjoyed working with over the years. Now, travel a bit to the South-East off their patch (but not as far as the coast); phew, now that's a different matter...
A well-trained but highly-insured human being has the passwords that let you change all the settings in the control system, and then the computer does all the busywork of actually running things. This frees up the human being to take laboratory samples, go look at things that have stopped responding, receive chemical deliveries, and all the other exciting jobs that water treatment entails. The plants don't quite run themselves, but can quite often be left to do their own things for weeks at a time without raising an alarm that needs a human being to go look at it *right now*.
Hopefully the description here has been over-simplified for IT people? Severn Trent's water treatment plants have a hierarchy of control:
- generally, each process area is controlled by a Programmable Logic Controller (PLC) - these are sat in a cabinet in a Motor Control Centre (MCC) and are responsible for monitoring instrument readings, starting and stopping drives, opening closing valves, that kind of thing. They're generally hardwired to each device; slightly more modern plants would use a token-ring networking system called Profibus to connect everything up, but Severn Trent are old-school. PLCs are hard-real time controllers about the size of a fag packet that use specialised programming techniques, usually ladder logic. The PLCs will have a local Human Machine Interface (HMI) screen, which shows the status of all the kit and all the set-points in effect, in pretty picture form, called a mimic. They're super simple and reliable; we've still got PLCs from the 60s that have just been ticking away every day.
- the PLCs are monitored over the network using a Supervisory Control And Data Acquisition (SCADA) system - generally over ethernet, sometimes ethernet over fibre optics if they're a bit further apart. SCADAs are generally server blades running Windows. They'll have a copy of the mimics for every HMI, so you can supervise the status of the whole plant; will let you change any set-point anywhere, which saves having to wander around the site to do it, and they'll have a lot of trending information available - they record all of the PLC instrument readings, so you can check how deep a tank was a year ago, for instance. You wouldn't want to outsource them; running a plant without one changes it from a one-or-two man job to an all-hands-on-deck, 24/7 cover disaster, and so an outage would be very very bad. Many of these sites are in the arse end of nowhere, and have unreliable internet connections: local, network-isolated Windows running on redundant servers can actually have a very good uptime.
- the SCADAs will report some telemetry info to STW's central database, so that the bods in head office can monitor the info. I think that's what's being proposed for changing over here? At the moment, STW only monitor a few key pieces of information (total plant flow, etc). United Utilities have been attempting to change over to their own system for the last several years, which monitors literally every piece of info for every asset they own, which is costing them millions per year in huge Oracle racks and which is very very slow; it's a prime candidate for moving to the cloud. STW are generally a bit more cautious and conservative, but can possibly leapfrog the 'do it on the premises' step - I think it would make a lot of sense. The SCADAs themselves generally keep years' worth of trending info stored, so they can buffer for a while if the networks go down and just update whenever otherwise - there's hardwired emergency callouts for things like power failures otherwise.
The three suppliers are Siemens, Allen Bradley, and Mitsubishi, I think. STW have been generally changing over from AB to Mitsi for all their control needs, but Siemens have been basically giving away the hardware and then stinging you for licenses and spares lately, and have been making inroads.
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