|
Not racing the beam as such, but spotting the beam, yes.
In around 1981 I built myself a UK101 kit computer; 6502 CPU, (originally) 4k memory and RF output to a monochrome television of 32 (originally 16) rows and 64 columns. Complete with full logic diagram. I'd made various mods to the system, but decided it would be cool to be able to "draw" directly on the screen. This in the days before mouse pointers, tablets, touch-screens etc. I knew the image on the CRT was a bright dot racing across the screen and figured if I had a light-sensitive diode, I could trigger a signal in response to the dot passing under it. That signal was connected to an interrupt and the interrupt processing code accessed what was effectively a hardware tick counter, that was synchronised to the clock for the video driver. Based on the value of that tick counter I could tell where the electron beam would be, and therefore I could calculate a character row and column.
So long as there were some pixels in the character, and a little adjustment to the TV brightness controls, it could detect the position of the light-sensitive diode pretty accurately. Fit the diode in the end of a "wand" and, hey presto, I could draw lines on the screen.
As you can see my grasp of it all was a little tenuous, but the excitement and joy when it actually worked was amazing... especially at the total cost of a few pennies and a couple of dozen lines of assembler code.
|
|
|
|
|
I built my first computer in 1978 and still have it. So you essentially built a light gun. I wonder, does shooting the (nonexistent) bea still work on modern monitors? do some game consoles even have light guns? It seems like I saw the last ones some time in the last millenium.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
IIRC, the NES one and some others will not work with modern TVs because they depended heavily on the CRT tech itself. We thought of it as "shooting the TV" but I might recall (or confuse with something else) reading the gun was technically being shot by the beam from the TV and then sending the angle of that back to the console and it would deduce from that where the gun was aimed.
There are newer ones (Wii and PS4 had them for sure) but they are based on different techs. The PS4 had these big balls of light on the controllers and a camera watched them. The Wii used some kind of IR system with a bar you put in front of the TV.
I suppose games are still "racing the ray" in a sense. It's just you don't get garbage on screen, rather, a frozen screen/choppy framerate if frames aren't coming fast enough.
|
|
|
|
|
Light guns (or light pens) Were not very complicated. you could build them yourself with some cheap parts from Radio shack. All you basically needed was a photocell, a button and a toy gun to put these into. Many graphics chips simply had registers that told the current position of the electron beam. When the sensor in the gun detected the electron beam, it must be pointed at exactly these screen coordinates. No wild calculation of angles or anything like that. But this of course does not work when there is no electron beam to detect.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
Wow, this really took me back 40+ years. While I never "raced the beam" I did plenty of other coding around interrupts (actual REAL interrupts, not the software abstracted ones of today) versus syncing up with the code.
|
|
|
|
|
Interrupts - what a luxury. On my old box I do bit banged serial communication without a UART. Currently all is well at 19200 baud. 38400 works for single bytes, but not for larger memory blocks. The timing error in the delay loops obviously accumulates too much when too many bytes are sent at once. Maybe I can resynchronize at every start bit, but I would have to overclock the old 8 bit processor a little more. It could go faster than 8 MHz if I raised the processor's core voltage above 5V. Perhaps it would then even become noticably warm and the processor would actually require cooling.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
Impressive! I never went below the UART interrupt level. Your mention of 8MHz reminded me of one of the things I tell my once a week Data Structures class that I teach - namely, that when I first started working with microprocessors the clock rate was in KHz, not GHz as they now are.
|
|
|
|
|
Fun times, sounds like. I never got that far back. I coded 6502 asm but Nintendo's hardware (NES) already had a pretty slick PPU that made timing somewhat easy.
Still coded in ARM32 asm for the DSi but that was mostly to do basic geometric transforms in the weird video memory it had (bitmaps were not stored in a straightforward manner).
|
|
|
|
|
The memory addressing logic was designed to let whatever graphics hardware you had access its video buffer quickly, not for the programmer's convenience. The hardware was racing the electron beam for you, so there was little time to waste. And then there is also the old problem of how to synchronize CPU and graphics hardware access to the same memory.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
I'm surprised no-one's mentioned ZX80 and ZX81. They didn't have specialised circuitry to handle the display, but, instead, had the Z80 execute the contents of the screen, ensuring that the Z80 itself saw only NOP until the end of the line. The contents of the data bus (the actual character codes) were then fed to the character generator.
|
|
|
|
|
Z80! Haven't heard that for almost 40 years, I used to write assembler for that, too.
You know this really means we are all a bunch of old farts!
|
|
|
|
|
|
I have that book in the shelf myself. A shame that all that pedal to the metal assembly code has been replaced by hard wired logic in some graphics processor since then. But things have been that way all along. Turns out that even my first computer kindof raced the electron beam, but it was automated via interrupts and DMA so all I had to learn was how to set up an interrupt routine and had not to worry about how to put pixels on the screen anymore.
The computer's design goes back to 1976. At that time having graphics at all were a complicated and expensive affair, so usually little single board computer kits did not have any at all. To make it not only affordable, but also relatively uncomplicated to use was a small wonder.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
I may have to build myself an MS-Dos (Circa 1995) computer, just so I can do some nostalgic programming again.
I do still have a set of Masm32 disks somewhere 
|
|
|
|
|
Ales with spirit point to starters (9)
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
|
|
|
|
|
Like it! 
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
|
|
|
|
|
Cheers, I hope someone solves it as we're becoming a monopoly again - I think it's largely the time difference - how's Mrs Griff ? sounded like a very nasty break to me.
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
|
|
|
|
|
Herself is getting more sleep, which indicates that it's getting better, albeit slowly.
I emailed you a pic.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
|
|
|
|
|
Got the email but no pic
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
|
|
|
|
|
Check the attachments - it shows as there in my "sent items" log".
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
|
|
|
|
|
Is it the email where you gave the answer to todays ?
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
|
|
|
|
|
No, a second one - you hadn't asked about Herself when I sent the first.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
|
|
|
|
|
It's just arrived Paul
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
|
|
|
|
|
I would oblige but in the car from 7am tomorrow so won't be able to do one.
|
|
|
|
|
No worries Rich
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
