MSX-C — A new, low-cost MSX Turbo R computer!

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Van konamiman

Paragon (1143)

afbeelding van konamiman

10-04-2021, 16:24

A few things that come to my mind after thinking a little more about the project:

First, my biggest concern is the absence of the DB9 ports. While you see these as merely joystick ports, that's not the only function they have; in the MSX world these ports are first-class expansion ports (used for stuff like mouse or trackpad too, for example) and I think the MSX experience isn't complete without these. The parallel port is a different story, it would be nice to have it but it's not as critical.

Second, this is how the list of features would be in my ideal world, in a must/nice separation:

Must have:

- Turbo Z80
- 2MB RAM
- V9958
- PSG+MSX-MUSIC
- 2 cartridge slots
- 2 DB9 ports
- Rewritable BIOS (all firmware ROMs, actually)
- RTC
- SD slot
- WiFi
- USB port

And nice to have:

- R800
- MSX-AUDIO
- SCC
- OPL4
- PCM
- V9990
- Ethernet port

SD slot is important as an alternative (or a complement) to flash storage, especially to store custom BIOS and downloaded software; that's much more versatile than fixed storage and allows for easy backups and offline customization.

USB offers endless possibilities of future expansion, for example to connect floppy disk drives, mass storage devices, or (almost) whatever we can think of.

Third, do you know the SX|2? Hardware-wise it's basically what you want to do minus the dedicated keyboard and the OPL4/V9990. Maybe you could contact 8bits4evver and perhaps join forces?

Fourth, and this is just brainstorming that might or might not make sense: maybe you could use some simple/cheap "all-in-one"-type small computer/board for the auxiliary, non-strictly-MSX part. For example, a Raspberry Pi W costs about 10$/€ and gives SD, USB and WiFi "for free"; this is just an example, I'm not saying it's the best choice.

And that's what I have for now, I hope this braindump is useful :)

Van JEckert

Rookie (22)

afbeelding van JEckert

12-04-2021, 17:01

AxelStone wrote:

+1 to change the name. MSX-C is already used by MSX C programming language, it's very confused to have 2 different things with the same name.

If it comes down to it, will have to change the name, but MSX-C is the right name to market, considering what the 'C' would stands for (consumer, cost-reduced, etc.)

Van JEckert

Rookie (22)

afbeelding van JEckert

12-04-2021, 17:17

For inputs, USB may seem like the best choice after all. We can program it to emulate MSX inputs depending on what is inserted.
I want to avoid DB9 for many reasons. They're more expensive compared to today's ubiquitous USB ports and underlying controllers. But as many of you know, DB9 was used on so many computers and games consoles at the time, and that means their pinouts differ. We shouldn't give the customer the opportunity to plug in something they're not supposed to and cause a short that damages the system or hurts themselves. Plus, USB is more ESD tolerant; if you spark your finger on a DB9 you can run the risk of damaging the IO controller on a real MSX. USB is more practical and less costly. Sorry for the DB9, but modern problems call for modern solutions.

Let's go over konamiman's proposed features and check off what we certainly want:
2MB RAM
V9958
PSG+MSX-MUSIC
2 Cartridge Slots
Rewritable BIOS (so firmware can be updated)
RTC
WiFi

Features that we should include:
Built-in keyboard
SCC
Moonsound
PCM
Ethernet

Features we want but may drop
SD Slot
MSX-AUDIO
R800
Turbo Z80
V9990

Features we should drop
DB9 ports

Van ren

Paragon (1860)

afbeelding van ren

12-04-2021, 17:39

Quote:

MSX-C is the right name to market

That's something that can be argued about. (I stick with what I said before: there's a naming conflict here, plus I simply find it dull (no offense) :))

Regarding USB/DB9: I don't really buy the 'protect the user from themselves' argument.
DB9 seems to have its use/place, though I figure USB <> DB9 converters exist? If that could interface with this MSX (with little to no latency (important I figure)), then that's an argument to just go with USB.

Van SergeyK

Supporter (2)

afbeelding van SergeyK

13-04-2021, 00:58

A few comments regarding previously asked questions, and some random notes:

  • Zilog still makes Z80 CMOS CPUs, the Z84C00xxyEG parts for example. They go up to 20 MHz (e.g. Z84C0020PEG), so there is plenty of room for "super turbo" if you want that. Using actual Z80 might increase the price - they go for $10 in single quantity ($6 when you buy a 1000). Another potential issue - most FPGAs have 3.3V (or lower) I/O voltage. The Z80 uses 5V power supply, and being CMOS IC, it has near 5V output voltage for logic signals. Luckily it has "TTL compatible" inputs, and it would accept 2.2V or higher as a logic "high" level. It might be possible to add some resistors between the CPU and FPGA...
  • To avoid issues with SD-RAM it is possible to use 512KB (or larger) SRAM chips. Again, this might add a bit to the price
  • I don't think generic DB9 to USB converters exists, or could exist at all. DB9 (or rather, the correct name is DE9), was used for many different purposes. You will find a lot of RS-232 serial (DB9 side) to USB adapters, which will not work with MSX peripherals.
  • I am not FPGA person, but knowing a bit about USB, it might be fairly difficult to implement a USB host in an FPGA. Not only that, it will also need to be a layer to emulate the MSX peripherals (e.g. a joystick) using USB peripherals. So, instead, it is be much easier to implement MSX ports (e.g. joystick ports).
  • SD cards on the other hand are really simple to interface to. They can use SPI protocol. A bit of software will be required to handle that, but nothing too complicated.

Van dhau

Paragon (1570)

afbeelding van dhau

13-04-2021, 01:20

I think MSX-C will be the best computer to run all the great games from Team RyJuZo!

Van lintweaker

Champion (414)

afbeelding van lintweaker

13-04-2021, 08:36

Maybe I missed it, you mention dropping the SD slot. What (modern) storage option is planned?

JEckert wrote:

Features we want but may drop
SD Slot
MSX-AUDIO
R800
Turbo Z80
V9990

Van AxelStone

Prophet (3032)

afbeelding van AxelStone

13-04-2021, 08:47

JEckert wrote:

Features we want but may drop
SD Slot
MSX-AUDIO
R800
Turbo Z80
V9990

Why dropping the SD slot? What kind of storage device are you thinking about? Also dropping Turbo Z80 is a shame because it provides a lot of possibilities to the computer.

Van Randam

Paragon (1369)

afbeelding van Randam

13-04-2021, 11:26

I am a big fan of everything Turbo R, but just a question; if you might drop r800 and/ or turbo Z80, what would be the turbo part? I hope you at least keep that part...

Van konamiman

Paragon (1143)

afbeelding van konamiman

13-04-2021, 16:09

Quote:

But as many of you know, DB9 was used on so many computers and games consoles at the time, and that means their pinouts differ. We shouldn't give the customer the opportunity to plug in something they're not supposed to and cause a short that damages the system or hurts themselves

I'm sorry but I don't think that this reasoning makes much sense in the (current) context of MSX computers. We've had DB9 ports in MSX since the very beginning and the case of someone damaging his computer by plugging a peripheral designed for another machine, while not impossible (probably, I'm not sure), is something I (active MSX user uninterruptedly since 1986) have never heard of (and even less someone hurting himself, if I am not mistaken we are dealing with 5V at most)... we could also say that someone could plug a cartridge backwards, but we don't advocate for suppressing the cartridge slots for that reason. I think I'm not terribly mistaken if I say that we in the MSX world (or the retrocomputing world in general, for that matter) are all adults and we know what we are doing (and if we don't but we want to experiment anyway, it's entirely our responsibility).

So allow me to insist because I really believe it's a very important aspect of any MSX computer design: DB9 ports are an integral part of the core MSX experience, aren't just for joysticks but for expansion in general, and shouldn't be left out in the same way as cartridge slots shouldn't; trying to be overprotective of users would be counterproductive in this case.

I'm sorry to be so insistent and I'm double sorry if I sound harsh (I don't intend to), also it's your project after all, but I really want this project to succeed and I really think that leaving out the DB9 ports wouldn't make that easy.

Quote:

Features that we should include:

I would include SD and Turbo Z80 in this list (for the reasons already commented by others), in exchange I don't think PCM and Ethernet are so important (especially if having WiFi, also Ethernet could be "easily" achieved via USB)

Also the built-in keyboard should be a must, otherwise you'll end up with something too similar to the already existing SX|2 :)

Quote:

I am not FPGA person, but knowing a bit about USB, it might be fairly difficult to implement a USB host in an FPGA

One step below not beign a FPGA person there's me, not a hardware person in general :) But it's my understanding that the FPGA part would be for implementing the core MSX part, and any extras (USB, WiFi) would be handled by other specialized components (e.g. a CH376 for the USB). The FPGA could just provide some kind of bridge (e.g. via one of the Z80 ports) to interact directly with those.

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