Search found 159 matches

by mc6809e
Tue Nov 19, 2013 5:48 pm
Forum: Hardware
Topic: Project idea: 16MHz CPU with faster ST RAM
Replies: 46
Views: 7396

Re: Project idea: 16MHz CPU with faster ST RAM

I think I quite follow you. How about using DE from GLUE to switch between the old MMU RAS/CAS signals and new RAS/CAS from extra logic? If that doesn't work, you might even use HSYNC and VSYNC along with a couple of counters running at 16MHZ and comparison logic to control the switch. What you tal...
by mc6809e
Mon Nov 18, 2013 4:53 pm
Forum: Hardware
Topic: Project idea: 16MHz CPU with faster ST RAM
Replies: 46
Views: 7396

Re: Project idea: 16MHz CPU with faster ST RAM

Video and MMU will work with original speed. As is described - you keep 250nS cycle for it . But CPU access to RAM happens at double speed as in normal STe . This needs some + logic and data storage for short periods - so will use latches, as is already done in original ST, but more chips. Will nee...
by mc6809e
Sun Oct 20, 2013 8:06 pm
Forum: Games - Requests
Topic: DOOM on atari st
Replies: 384
Views: 76646

Re: DOOM on atari st

While there are plenty of problems with performance of compiled code when looking closely at it, I think the most significant one is the fact that high level languages don't translate structurally to optimal assembly programs, because there is no sense of resource competition. Yeah, they seem to fo...
by mc6809e
Sun Oct 20, 2013 4:47 pm
Forum: Games - Requests
Topic: DOOM on atari st
Replies: 384
Views: 76646

Re: DOOM on atari st

Bit of an update on this today. The decision to break the code up into several smaller, simpler passes with buffering of small packets in between each pass turned out to be a good one - it depends on the packets being as small and simple as possible but it does work well. e.g. the raycaster generat...
by mc6809e
Mon Sep 23, 2013 7:10 pm
Forum: Hardware
Topic: ST vs Amiga : advantages/disadvantages
Replies: 180
Views: 37704

Re: ST vs Amiga : advantages/disadvantages

7MB/s?!? how is it possible??! How "fast" is FastRAM in Amiga500 (32bit bus on 7.14MHz??)? MC68000 8MHz can "transfer" up to 4MB/s right? Memory can be accessed as quickly as every two CPU cycles, though the CPU isn't fast enough to take advantage of this, limiting CPU memory ac...
by mc6809e
Mon Sep 23, 2013 6:27 pm
Forum: Hardware
Topic: ST vs Amiga : advantages/disadvantages
Replies: 180
Views: 37704

Re: ST vs Amiga : advantages/disadvantages

I have 2 GVP sidecar drives. I had one in 1992 too but it died :( I never seen the drives transmit more than a meg a second. Certainly faster than the IDE hard disks around on the 600 etc at the time. The SCSI controller on the board isn't custom. It's off the shelf if I remember correctly. Should ...
by mc6809e
Mon Sep 23, 2013 1:54 pm
Forum: Hardware
Topic: ST vs Amiga : advantages/disadvantages
Replies: 180
Views: 37704

Re: ST vs Amiga : advantages/disadvantages

How fast is the GVP hard drive then? Sent from my Nexus 4 using Tapatalk 2 Considerably slower than the ultra satan I'd wager. The ST had a blazing fast DMA controller built in from day one. The controller on the GVP had to be implemented on the device itself/ The Amiga really missed an opportunity...
by mc6809e
Wed Sep 18, 2013 11:13 pm
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

But there's a deeper can of worms here: what is the accurate definition of 'cycle 376'? ... So what I'm trying to answer is the root hardware defining "what is cycle 376'"? What does zero mean in this numbering system? Is the write actually happening on cycle 376, or is it cycle 377? Wher...
by mc6809e
Mon Sep 16, 2013 10:58 pm
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

Of course, but, poking the Shifter (820a) at cycle 52 will produce an NTSC starting position instead of PAL - and if the actual pixels also are displayed at cycle 52 (and 56 respectively) then I can't imagine how there would be time for anything else to be involved. They're not. They appear on the ...
by mc6809e
Mon Sep 16, 2013 6:20 pm
Forum: Hardware
Topic: ST vs Amiga : advantages/disadvantages
Replies: 180
Views: 37704

Re: ST vs Amiga : advantages/disadvantages

No, the amount of refresh done in the ST is overkill. You only need to refresh each page once every few ms (4ms for the Fujitsu RAM in mine) - during the screen period, this actually occurs naturally, since the video is arranged so adjacent words are on different pages; it therefore reads 160 pages...
by mc6809e
Mon Sep 16, 2013 4:54 pm
Forum: Hardware
Topic: ST vs Amiga : advantages/disadvantages
Replies: 180
Views: 37704

Re: ST vs Amiga : advantages/disadvantages

hm... just one more thing: I suppose that RAM does not need so much refreshing cycles (16.000 in case of ST)? how this is done in Amiga? Does refreshing cycles occur between CPU cycles? and if there is so much free time of RAM in ST, could Atari gave e.g. 64KB for frame buffer? There are four refre...
by mc6809e
Mon Sep 16, 2013 4:51 pm
Forum: Hardware
Topic: ST vs Amiga : advantages/disadvantages
Replies: 180
Views: 37704

Re: ST vs Amiga : advantages/disadvantages

On the ST many of those memory access cycles are simply turned into memory refresh cycles and can't be used by anything else. On the Amiga they are available for work. I'm not sure about that. I would think that in the ST memory refresh is done in the same manner as in Amiga, it takes only a few cy...
by mc6809e
Sun Sep 15, 2013 7:23 pm
Forum: Hardware
Topic: ST vs Amiga : advantages/disadvantages
Replies: 180
Views: 37704

Re: ST vs Amiga : advantages/disadvantages

Atari cpu cycles/frame = 508*263 = 133,604 cycles. ... Amiga has 226*263 = 59,438 memory accesses/frame can you explain what this numbers mean? and help me to understand your post :) why 508 * 263? what is 508? and what is 263? (and 226 and 263 on Amiga?) Those numbers are for NTSC machines. For NT...
by mc6809e
Wed Sep 04, 2013 2:26 am
Forum: 680x0
Topic: Blitter HOG / Blit mode
Replies: 9
Views: 2852

Re: Blitter HOG / Blit mode

Actually it works. Blitter needs to be started with so called "Class 0 instruction" : http://pasti.fxatari.com/68kdocs/68kPrefetch.html Six or seven years ago I did some tests and I posted somewhere on AF some screenshots from STe Very nice trick! So basically you get the CPU to do all in...
by mc6809e
Mon Sep 02, 2013 2:31 am
Forum: Chat forum [ENG]
Topic: The birth of Atari ST
Replies: 33
Views: 7621

Re: The birth of Atari ST

IMHO the Megadrive was a much bigger thread to the Amiga than to the ST. I still see cheap PCs with Windows 3.1 as the ST and Falcon killer. Those who could afford, bought Macs, those who did not moved to PCs in the 90s except for a small small minority. Don't underestimate the degree to which the ...
by mc6809e
Sun Sep 01, 2013 7:29 pm
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

Again, the shown color is not a direct intermediate value between the previous and next color: it depends mainly on the next bitmap word. That's a interesting find. It could be that while the MMU is controlling some of SHIFTER's control lines for a CPU write to the palette registers, it also has bi...
by mc6809e
Sun Sep 01, 2013 4:13 pm
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

This means probably that the power "on" burst will send a RESET at slightly different times for each individual chip. As the Shifter works at 32 MHz, it is even more sensitive to these different starts and can then have 4 different phases compared to a 8 MHz chip. If i am pressing the war...
by mc6809e
Sun Sep 01, 2013 5:34 am
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

As near as I can tell there seem to be two things happening: 1) GLUE is in one of four phases relative to the MMU's CPU/SHIFTER memory access cycles. 2) In one or two of these phases, the CPU can touch GLUE's internal registers at times that straddle some critical point when GLUE is updating interna...
by mc6809e
Wed Aug 21, 2013 8:02 pm
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

If we can see any 'warmup' cases which only depend on syncmode, then I can look at those. But as I understand it all the problem cases are on the resolution register only, and I suspect all those are inside the shifter. (Although the actual change in timing may not be entirely sourced there, since ...
by mc6809e
Tue Apr 23, 2013 12:09 am
Forum: Demos - General
Topic: Display Trick Idea - would like some thoughts...
Replies: 26
Views: 13112

Re: Display Trick Idea - would like some thoughts...

I think on the Amiga it's possible every 4th pixel. The copper does half on the even cycles and the CPU does the other half on the odd cycles. Bitplane DMA must be turned off, however, to make room for the CPU. I always thought that the Copper in the Amiga could do a 4 pixel write either with trick...
by mc6809e
Fri Apr 19, 2013 8:46 pm
Forum: 680x0
Topic: Lance 12.5 / 25 / 50 KHz routine for STE (V13)
Replies: 71
Views: 20289

Re: Lance 12.5 / 25 / 50 KHz routine for STE (V9)

Getting a 50KHz output rate using just 40% CPU time is impressive.

I remember writing a 4-voice polyphonic synth for a 6809 machine years ago and shaving away every cycle I could just to get an 11KHz output rate. I bet you're really enjoying yourself :).
by mc6809e
Thu Apr 18, 2013 3:13 am
Forum: Demos - General
Topic: Display Trick Idea - would like some thoughts...
Replies: 26
Views: 13112

Re: Display Trick Idea - would like some thoughts...

it is not speed of computer/CPU but rather design or "organisation" of computer... could Amiga do the trick? this is due to bus bandwidth which is determined by memory access time. Exactly the same issue exists in Amiga where during visible a line Cooper can change color every 8th low res...
by mc6809e
Wed Apr 17, 2013 12:54 am
Forum: Demos - General
Topic: Display Trick Idea - would like some thoughts...
Replies: 26
Views: 13112

Re: Display Trick Idea - would like some thoughts...

A single blitter write takes 4 CPU cycles. One read and one write take 8. Every 8 CPU cycles is 16 pixels so the blitter is too slow for this.
by mc6809e
Thu Apr 11, 2013 2:45 pm
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

About your code : In your prologue lsl instruction will clean right bits of the LSW but not the ones of the MSW. So when it cames to "or.l d4,d2" and "or.l d5,d3" before le writing the first block you'll get graphic gliches. In addition, i'm pretty sure that move.l (an)+,dn and ...
by mc6809e
Thu Apr 11, 2013 3:03 am
Forum: Coding
Topic: horizontal scrolling on ST
Replies: 575
Views: 143215

Re: horizontal scrolling on ST

I like Paulo's way. Modifying Paulo's code a little I get a total of 2512 cycles per scanline for a 3 or 4 pixel shift. The two pixel shift is 2352 cycles leaving about 10,000 cycles free at 16.67 fps. Not a lot. But maybe enough for a simple scroller. ;a0, a1 point to beginning of scanline ;d7 is s...

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