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How About: Full Banks Standard?


rje
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The FAQ notes that 512k banked RAM is the planned shipping configuration.

i reckon this is a cost consideration.  But isn’t it likely to cap programs to only use 512k?  It feels like a handicap, however minor.

 

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It's extremely minor, and easily overcome. 512k is still an embarrassment of riches for an 8-bit computer, and it means that it can act as a baseline for compatibility, and pretty much any game or application that will work within 2MB can work in some form at 512k. A program can detect the number of banks and load extra data into the higher banks for quicker access. This can make having more RAM act as a cache to mass storage to cut down on load lag. Or extra RAM can enable things like more music and sound effects, so the user experience is enhanced. If a program absolutely needs 2MB to be functional, that would definitely hamper its adoption, and chances are it could have been more intelligently designed to make it work in some form in 512k.

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Posted (edited)

That's sort of what I am thinking, except on the opposite side.  TOOLS as well as games will be written for 512K.   They COULD do RAM cache, but I suggest it's easier to make do without, unless you absolutely have to.

As you say, it is an embarrassment of riches, and so we can live without the other 1500K, and I think we will.  😞

Your examples have some merit though.  I could see a music or effects cache, and if there's a cheap and easy way to leverage that, then I could see it.  Assuming ... well assuming lots of things.  

This is a weird ecosystem.  But the part that's NOT weird is how like Commodore this process is.  Take a stab at things, have possibilities, but in the end you don't really know what sort of impact it will make.

***

I use the banks statically: I load them once and use them.  But I could see a cached solution.  Hmm.

Edited by rje
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What is the cost difference for 3 more 512x8 SRAM ICs? 20 bucks US? If it's 10% of the total cost, I'd say it's worth it to make them all 2Mb machines, and make that the lowest common denominator, because the LCD is what programmers will write for. Quadruple the embarrassment!

Having said that, here's some assembly language code to determine the max RAM bank number:

LDA #FF
STA 00
STA A000
SEC
SBC #40
CMP #FF
BNE #F4
STA 00
CMP A000
BEQ #07
SEC
SBC #40
CMP #3F
BNE #F2
RTS

Edited by Ed Minchau
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Lowest Common Denominator is what I'm thinking about.  I would REALLY want to use the full 2MB, and if I do that, I won't want to write code that accommodates a 512K system... except I'm kind of hamstrung, aren't I, into coding to LCD, in which case forget the 2MB version... But the developer inside of me says "make a decision, do one or the other and stick with it".

Note that I wouldn't have been thinking this way if Eight Bit Guy hadn't specifically TALKED ABOUT IT in his videos on the VIC-20, Plus/4, et al.

 

 

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Posted (edited)
On 6/20/2022 at 12:19 PM, Ed Minchau said:

What is the cost difference for 3 more 512x8 SRAM ICs? 20 bucks US?

Total?  Somewhere around there, it seems.

Quote

 If it's 10% of the total cost [...]

Nickels and dimes add up.  But yeah. 

Edited by rje
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Another cost consideration is the move to a single FPGA design. Quadrupling the RAM would likely be much more than a 10% increase in cost. And even with discrete through-hole RAM chips, as we have seen, the market for chips like this has gone whackadoo (I apologize for using such a technical term), with demand outstripping supply by an order of magnitude (or more!), as chip fabs put their limited resources to producing high-quantity, high-profit components for modern systems. Prices for the kinds of chips used in the X16 have doubled in the last couple years, if not tripled or worse! And supplies being how they are, there may simply not be enough RAM chips available to put more than 512k in every unit. We could even be looking at a lottery situation for completed X16 units at first.

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There's also the kit factor. If you get a board with pads/vias for more RAM, you can try your hand (literally) at adding the RAM yourself. Not that everyone will want to do this or even be able to do it.

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Removing 3 RAM chips and the support demux also saves considerable board real estate. No telling which way Kevin will take the official board, but the prototype PCB for my design left them out to save on board space and fit the whole thing into a mini-ITX form factor. I left a header and jumper for expanding the RAM if I ever felt the need. $20 extra in BOM cost does not mean $20 extra in sticker price - I hope everyone realizes this. When you start manufacturing these things you have to add margins to account for production losses (bad components, bad boards, customer returns, and on, and on).

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On 6/21/2022 at 8:43 PM, Wavicle said:

Removing 3 RAM chips and the support demux also saves considerable board real estate. No telling which way Kevin will take the official board, but the prototype PCB for my design left them out to save on board space and fit the whole thing into a mini-ITX form factor. I left a header and jumper for expanding the RAM if I ever felt the need. $20 extra in BOM cost does not mean $20 extra in sticker price - I hope everyone realizes this. When you start manufacturing these things you have to add margins to account for production losses (bad components, bad boards, customer returns, and on, and on).

Last I heard, the official story is that the sockets would be there, but that only one out of the four would be populated. So unless the plans have changed, the chip select and other hardware will be on the board. We're literally just talking about 3 memory chips.

 

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On 7/30/2022 at 5:39 AM, Fabio said:

could the extra ram chips be moved to an expansion board?

In theory, but it would require changes to the expansion slots, and it would make the extra RAM more expensive, rather than less. 

At this point, if they want people to actually be able to use 2MB of RAM, the cheapest alternative is to leave the sockets in place on the board, but not populate them. 

 

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Since I don't consider the Panasonic MSX Turbo-R Machines to be 8-bit computers (the ASCII R800 featured 16-bit integer instruction arguments, registers, and at least one 16-bit data bus), the 8-bit computers with the most standard RAM would be the final production year Tandy CoCo 3 and Fujitsu FM-77, with 512-640K system RAM each (plus 128-384K separate VideoRAM in the case of the FM-77 AV40 Level 3).  That said, the Apple IIc+ and IIe Anniversary Edition, Sharp X-1 Turbo Z and X, and NEC PC8816/18 have O/S memory maps capable of addressing up to 2MB, and Atari 8-bit computers equipped with the FREDDIE MMU/DMA can address up to 4MB.

Back in the day, two full megabytes of High RAM+124K Video RAM, 4K PCM Buffer, and 64K Low RAM would together be seen as overkill until Ca. 1990-91, with only the Apple IIGS and Amiga 750 and then 1200 possessing similar memory amounts among contemporary non-PC Clone competition.*

 

*I do not consider the Macintosh III and Quadra, Sharp X68000, High End Amigas, or Acorn Archimedes A4000/A6000 series to be anything close to hypothetical market segment competitors.

Edited by Kalvan
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Make a DDR2 etc DRAM interface using an FPGA which have a DIL socket under it. Behaves like a RAM chip but way more availability.

The important thing is to make sure all relevant (address) signals are available in the socket. One option is to place another smaller DIL socket inside the larger than such that ordinary RAM chips use the standard pins but a special board may enable even more (D)RAM by using extra high address signals from a center connector.

 

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On 10/19/2022 at 3:43 PM, neutrino said:

Make a DDR2 etc DRAM interface using an FPGA which have a DIL socket under it. Behaves like a RAM chip but way more availability.

The important thing is to make sure all relevant (address) signals are available in the socket. One option is to place another smaller DIL socket inside the larger than such that ordinary RAM chips use the standard pins but a special board may enable even more (D)RAM by using extra high address signals from a center connector.

 

Once again, this isn't going to happen. There are no more planned changes to the hardware, and if you have an idea for a hardware product, you should be prepared to design and build it yourself. 

An REU-like memory expander is possible, but there is no way to fully bank out memory on the mainboard. That design feature was intentional, as David wanted the memory banking to be as simple as possible. So if you have an idea for your own memory expansion module, you'll want to figure out how to build it within the constraints of the expansion ports. As in:

  1. Each port gets 32 bytes of I/O space. If I recall, there are actually give 32-byte blocks, so your card will need to be able to select from one of those blocks.
  2. Your card can read from and write to main memory, but it must follow the DMA process outlined by @Lorin Millsap here: 
  3. There are four expansion slots, so your card must get along with cards plugged into the other slots. IE: it needs to stick to its 32 bytes of address space and not try to tie up all the I/O space for its own use. If you want to store stuff in expansion RAM, it needs to go through the 32 bytes in that card's slot. How you do that is up to you, but I suggest you read up on how the Commodore 1750 REU works as an example.

 

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