12 November 2021, 08:23 | #621 |
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Thanks for the details on midi. Indeed, PAULA could have profited from a serial input FIFO for higher baud rates, indeed. Contemporary PC serial interface chips had a four-bytes receiver side FIFO which helped for higher baud rates. PAULA was, however, just an upgraded POKEY design with its single-byte fifo.
Actually, the Atari design already showed that the Pokey input buffer of one byte was close to the limits at the SIO transfer speed of 19200 bytes, so I wonder why that wasn't changed, or PAULA wasn't upgraded along with AGA. |
12 November 2021, 11:25 | #622 | |
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But if we are comparing the Amiga serial port's MIDI performance with that of the PC then whether it used a 16550 or 8250/16450 is irrelevant, because neither was capable of the 31.25k baud rate required. That is why to use MIDI on a PC you needed a special MIDI port, which typically was included on sound cards (most of which still needed a MIDI interface cable to convert the TTL serial signals to optocoupled I/O). Last edited by Bruce Abbott; 12 November 2021 at 12:08. |
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12 November 2021, 12:03 | #623 | ||||
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This reminds me of a music program by Gold Disk called 'Music' that was bundled with the A500. They made the fundamental mistake of using an 8 color hires screen, which sucked bandwidth from the CPU making response sluggish. Nobody who understood the basics of Amiga hardware would make that mistake. Makes me cringe to think how many A500 users got their first impressions of the machine's capabilities from this poor effort. Quote:
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12 November 2021, 13:29 | #624 | |
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12 November 2021, 14:40 | #625 | ||
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So, is the Amiga able to do the same? And if yes, are the mechanisms to handle errors in the MC6850 are as well effective in the Amiga? For the record here is the extract of the MC6850 documentation for the receive part: Quote:
Last edited by TEG; 12 November 2021 at 14:47. |
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12 November 2021, 14:51 | #626 |
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PAULA behaves in this respect the same as POKEY, its direct predicessor - and exactly as the 6850 ACIA. It is also double-buffered. While the receive register is being filled, the previous copy can be retrieved by the CPU.
However, the serial port does have problems catching up data at high bitrates, which is why we have these "RADBOOGIE" mode of the serial device which bypasses a couple of tests just to speed up interrupt processing. A four-bytes FIFO would have helped. |
12 November 2021, 15:03 | #627 | |
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Yeah, I forgot about what you said in your previous post about POKEY buffer while I redacted mine. So Dave Haynie sentence was a bit over-simplified or his memory played him some trick. So I conclude that both machines serial port are buffered but the Amiga needed a larger one due to multitasking or simply Interrupts design. |
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12 November 2021, 18:51 | #628 | |
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Its really not like there is no working MIDI-software for the Amiga:
https://aminet.net/package/mus/midi/BarsPipes-demo https://aminet.net/package/mus/midi/horny-68k https://aminet.net/package/mus/midi/MIDIMon https://aminet.net/package/mus/midi/MIDIPlayground https://aminet.net/package/mus/midi/MIDIstuff_II Or: https://aminet.net/package/docs/hard/TriplePlay2 Quote:
That said: CBM could have made it a lot easier and better. As discussed elsewhere on EAB, sound generally should not have been that closely coupled to the gfx-chips. Paula/Portia should have been combined with CIA and DMAC and probably some FiFos as an independent unit of the system. |
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12 November 2021, 19:12 | #629 | |
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Now you exaggerate. We don't say it can't, we say it was not perfectly reliable. Testimonies (and history) seems to go into this direction. Of course it would be better to have first hand experiences to be sure. |
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12 November 2021, 20:36 | #630 | |
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of course they could use multiplierless YCoCg color space however it was invented by Microsoft around 2003... So HAM is RGB limited and RGB itself was sane decision - all computer technology showed that analog RGB was and still it is right choice. Side to this YUV equation are different for NTSC and for PAL and if Amiga will go for YUV internally then it would need also different scaling factors for Y, B-Y, R-Y as they are not the same for NTSC and PAL so even more complicated design. In theory there is nothing against coding HAM as YUV and transform YUV embedded on RGB lines to proper RGB externally even nowadays - or instead YUV use YCoCg color space... This could be embedded to modern (FPGA) Denise/Lisa re-implementation as feature that can be controlled by Copper so MPEG/H.264/H.265 video could be decoded without time consuming YUVtoRGB step... TTL-RGB was extensively used by all external video modifiers (DCTV, HAM-E, A2024 etc). Another topic is a MIDI - even on PC most popular MIDI UART was MC6850 (present in Atari ST) - definitely there is no FIFO there, simple external oscillator make possible to produce 31250bps - not possible on PC due NTSC derived frequency (same as on Amiga where system clock is tailored for NTSC or PAL) - simple freq divider prevent PC and Amiga to get 31250 bps. This lead to biggest Amiga limitation directly affecting audio and serial capabilities - lack of the NCO - with NCO (16 bit NCO means 4 x 74283 - not much when compared to overall system complexity) instead simple digital frequency divider, Paula immediately get proper (music friendly), fine control over sampling frequency and also serial will get way more functionality due possibility to select usable transmission speed (as single NCO can be shared with 4 audio channels and serial port). Atari ST deals with simple MIDI because it is not multitasking machine so reaction for interrupts is less affected by latency and associated jitter. FIFO is mandatory for multitasking systems and that's why it was introduced on PC - to deal with time critical events... btw forgot to add but 1 bit DA converters was understood and properly designed around 5..8 years after Amiga, also dithering and noise shaping is something that was born way after 1990 - single bit DA in Amiga is not feasible if full Paula compatibility is goal (to do 1.79MHz sample rate and at least 20..32 times oversampling necessary for delta sigma then we need at least 30..50MHz clock and design - probably beyond MOS Technology/CSG capabilities as they struggle with 28MHz designs - ECS Denise palette shuffling and limitations - probably they introduced some form ot time interleaving so probably CSG was incapable to do something more complex above 25MHz). Last edited by pandy71; 12 November 2021 at 20:44. |
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12 November 2021, 21:29 | #631 | |
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How created CRTs RGB color from YUV? Analogue, of course, but I would expect that originally no RGB output was considered, but this was probably relatively late adjustment. |
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12 November 2021, 22:24 | #632 | |
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Why would you do that? You just stay in the YUV space all the time, for all digital purposes. (The only (analog) conversion one might do is at the output, where it is done in the A1000 as well - just in the other direction.) |
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12 November 2021, 23:31 | #633 | |
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https://ieeexplore.ieee.org/document/1095151 H. R. Schindler, “Delta Modulation,” IEEE Spectrum, Oct. 1970 (with circuitry) H. S. McDonald, “Pulse Code Modulation and Differential Pulse Code Modulation Encoders” U.S. Patent 3,526,855 filed Mar. 18, 1968 H. Inose and Y. Yasuda, “A Unity Bit Coding Method by Negative Feedback,” IEEE Proceedings, Nov. 1963. And no: we do certainly not need "30..50MHz" for that! The Super Audio CD has only a 2.8 MHz sampling frequency for it's bitstream. Last edited by Gorf; 12 November 2021 at 23:37. |
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13 November 2021, 01:24 | #634 | ||||
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There is no consumer TV equipped with YUV input, some broadcast monitors may have Y, B-Y, R-Y inputs but still this is not YUV - recently (with HD introduction i.e. almost 30 years ago) YPbPr component interface was present at TV's - mostly US but still this is not YUV but rather something like RGB. Most if not all "YUV" based computers are simple delay logic where "sine" and "cosine" are created as taps in some serial shifter - good for maybe 100..200 colors. So you can have FBAS or rather CVBS or perhaps S-Video (Y+C where Y bandwidth is max 5.5MHz and C bandwidth somewhere around 2..3MHz). RGB was simply better as native representation natural for video world (cameras and displays work natively in RGB space) Quote:
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SACD has only 2.8MHz but comparable bandwidth to PCM with sampling around 50ksps - Paula 8 bit PCM sampling rate is 1.79MHz so you need to oversample signal at least 20..32 times to get comparable 8 bit quality (around 40..50dB) in Delta Sigma (my assumption is that they will use first or second order Delta Sigma max due stability issues for higher DS orders). Btw FPGA DS DAC implementations are usually clocked with 50..100MHz and still they are rather poor DAC's (somewhere around 60dB i.e. 10 bit quality). |
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13 November 2021, 02:52 | #635 | |||||
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You can derive the composite signal even easier from YUV than from RGB, since the Y is actually luma... Same goes for S-Video. There is absolutely no benefit to having a RGB signal except for dedicated monitors with RGB input. As a reminder most CGS or EGS pc-colormonitors, the most common monitors back in 1985, had only digital RGB color inputs and 16 fixed colors ... but most also had a composite input ... Real analog RGB monitors became only fashionable with VGA. So it is actually a little bit awkward, that CMB was insisting on RGB, while they were in a hurry to get then chipset done... Quote:
Later it was an advantage, but by then an additional RGB output could have been added to new models. On the other hand: all video codecs as well as jpeg use some kind of YUV, and it would have been also easier to implement some Gouraud shading when early 3D games become fashionable. (the Atari Jaguar did this) Quote:
99.9% of all programs or games for the Amiga perform no operations on the color-space. With YUV you only fill your colour registers with slightly different values. And the firs 4-bit nibble of your 12-bit value would be Y = brightness. So it you want a slightly darker tone of the same colour, you just lower the first nibble by 1. Quote:
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Just because Paula treats 8bit-samples internally up to 1.79MHz it does not add any information to it (except loudness). It is just repeating the same value up to 64 times ... So this are just some inner workings of Paula that do not matter at all, if you would design a new chip with sigma-delta output in mind. You only have to take the PCM sample frequency as it comes from RAM into account. There are a lot of discrete circuit designs from the 70s and early 80s around doing just that ... AT&T was experimenting with that for voice transmission and finally AMD mass-produced a modem-chip with sigma-delta DAC in 84... So yeah, it would have been bleeding edge technology, but not impossible. |
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13 November 2021, 06:02 | #636 | |
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The Jag actually used CRY, its very own color model developed by flare. Similar to YUV (luminance + two color components), but not the same, and it's not straightforward to convert from CRY to YUV. |
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13 November 2021, 06:41 | #637 | |||||||
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The idea that Commodore only put RGB in the Amiga because they were in a hurry is laughable. Analog RGB was considered the gold standard for video displays, which is why IBM used it in their high-end systems (and later for VGA). RGB is the natural method because that is how our eyes see color. Composite/YUV was only invented to get around the severe bandwidth limitations of broadcast TV. It sucks, but was the only way to 'compress' the color information to be compatible with monochrome transmission. Unfortunately it continued to be used in the digital age (for similar reasons). I have a Samsung SyncMaster 940MW LCD monitor/TV. These are very rare in New Zealand because we didn't embrace SCART here, but I was lucky enough to get one from the local op shop for $75. It's a good screen except for one very annoying limitation - the upscaler only works with YUV encoded color, optimized for low bandwidth composite - so it first coverts the RGB to this format before upscaling it. I got into the secret service menu and turned off every 'enhancement' I could that was trying to compensate for the lack of color bandwidth, but it still applies some edge enhancement. The SCART RGB picture is 'OK', but would be so much better if they had upscaled it directly! Quote:
Slightly OT - in New Zealand the importers hot-glued a bung over the composite input on Amiga monitors. Why? Consumer electronics attracted 40% sales tax, but computer monitors were a 'business' item so the tax was only 25%. Of course customers simply pulled the bung off as soon as they got it home. Quote:
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13 November 2021, 08:54 | #638 | |
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TV signals are all YUV based. Of course not YUV-component based, but composite or FBAS, which was the conventional form how home computers back then supplied a signal to a monitor. Of course, the quality is worse due to the lower bandwidth, which was probably the reason why they changed their mind.
Certainly, all of them, or most of them, just that it's modulated. FBAS, or component, as I said. Quote:
But this was exactly what was happening. Originally considered a games console, they changed it into a PC. HAM was originally for YUV, and there it would have made more sense. Actually, instead of HAM, 422 sampled data (YUYV) would have made even more sense. |
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13 November 2021, 08:58 | #639 |
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But not the brain behind the eye. The human vision system is much less sensible to hue variations than to luma variations, so something like YUV that separates out the luminance makes a lot of sense.
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13 November 2021, 14:51 | #640 | ||||
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(Or are you talking about these RF-modulators? These are terrible of course, but that’s a different thing.. ) If Denises output was YUV the composite (and S-Video) output would have been better. Quote:
CMB changed the design of the custom chips from YUV to RGB despite of being in a hurry to get the new machine out! That is the strange thing… Quote:
In this case native YUV would improve the signal quality. Quote:
You take this out of context here. At this point the discussion was about general advantages of the RGB colour-space in computing, so I brought the counterargument of video-codecs and shading. |
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