Streaming video on a Sinclair Spectrum

Ethernet card for the Sinclair ZX Spectrum and a demonstration of streaming video to the Spectrum.
See http://spectrum.alioth.net/doc for more information.

Category:

Science & Technology

Tags:

• streaming
• video
• zx
• spectrum
• ethernet

[jbase44]

I used to program for Speccy a lot when a kid.

Its probably something like:

LD HL,#4000

IN A,(#FE)

LD (HL),A

INC HL

JP .....

Is that it? You are sending complete bytes to Speccy. Or, you're probably using INIR command, port input in a loop? That would be pretty fast, I guess. ZX didn't have a DMA though.

Memories... Oh, those memories. Bring them back...

[74HC138]

@jbase44 It's a memory mapped device, so LDIR to copy out the ethernet buffer to screen (a sequence of LDI instructions would be faster). When the spectranet is paged in there are 4 x 4K pages in the memory map between 0x0000 and 0x3FFF, two of the 4K pages (lowest and highest) are fixed but the middle two can be paged as RAM, flash ROM or ethernet buffers.

[jbase44]

@74HC138, oh that's not exactly fair then. ;) Back in 90-s we didn't have the luxury of memory mapping an external device or paging video RAM although some other Z80 and 8080 based computers had it. One could use paging to produce smoother animation.

[74HC138]

@jbase44 It makes no difference that it's memory mapped, INI and LDI both take the same number of T-states, and the data still has to be copied from the ethernet chip to the frame buffer. Since I already have to have all the paging for the ROM and extra RAM, might as well memory map the ethernet buffers too since it simplifies the design of the glue logic. (The Speccy 128K does have paged screens, btw, so you had paged video ram in 1986 with the original 128K :-))

[harryhardest]

25 years ago you would have been rich!

[pufixas]

@harryhardest

25 years ago, there was not such technology as now, and he couldn't make it that easy

[Squiddy200]

@ToricoUK The trouble is it would of been all blocky..but with no colour clash :p

[MarkP0rter]

ha why are you watching RTL II? that's a German station.

[68HC060]

uhm.. Try setting sp, then push : push : push : push : push ... it might be faster.

Anyway, very nice. I just wish it was demonstrated on the original 48k model. ;)

To "expand" pixels, you could probably AND with 170, then write, then XOR the original and write in a line somewhere below; you'd have split every 2nd pixel, so you'd have to mess up the datastreem at the source, but you might get an even better performance.

Anyway, good work!! :)

[eggnogonthebog]

Good black block quality

[drewish]

nice hack

[malc1976]

Is that film Terminal Invasion? think i just seen Bruce Campbell

[summer20105707]

@syrus3k

These eight bit computers from the eighties had loads of potential that were never realized back in the day. All of them did great things if put into the right hands.

[ToricoUK]

I'd like to see this on c64

[twotimesqwertyuiop1]

I remember from Z80 instruction LDIR its very fast - as DMA :)

[TableWolfMusic]

I'm trying to get my head around this having watched arduino microcontroller video players (of similar black & white quality). From what I gather, lets say they have a microcontroller (amtel) hooked up to a nokia 3310 screen or equivalent, each bitmap pixel is drawn to the screen. No discrete cosine transform compression of anything fancy. My understanding is sketchy. So this spectrum just grabs the image on screen from the video stored on the PC, regardless of the codec. Is that correct?