msxdos2 question

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Van PingPong

Prophet (3898)

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03-03-2022, 00:19

So, this means, for example that there is no standard minimal sw interface for disk drives, ( disk are not a msx standard ? ) ?

there is no standardization for msx disk devices, i guess- not a single row of specifications - am i right?

Van Grauw

Ascended (10602)

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03-03-2022, 01:47

I don’t understand what you mean? Disk BIOS is completely standard, although optional as seen even in the MSX2+ generation (Sanyo Wavy PHC-35J). Disk drives are one of the few instances where developers rarely dare to access them directly and bypass the BIOS. Since there are so many disk controllers it really shows the benefits of having a standardised BIOS for it. It would be an incompatible nightmare situation otherwise (like it is for MIDI, for example).

Van PingPong

Prophet (3898)

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03-03-2022, 02:11

i mean something like the VDP or PSG. msx computers must have a VDP compatibile hw chip.
For disk drives there is no such kind of spec. (for example a specific FDC controller)

Van Briqunullus

Hero (525)

afbeelding van Briqunullus

03-03-2022, 08:52

Diskdrives can vary wildly, take the SVI-707 for example. That's a 5,25 inch drive. The MSX doesn't know. It uses the diskrom to access it and the physical device doesn't matter.

PingPong wrote:

I remember my NMS8245 (msx2) booting msxdos1 without any cart. But it was msx2.
What's the difference?
Is only due that msx2 models with built in drives have also built in bios?

Yes, the 8245 has a built in diskrom. See that as an internal cartridge.

It's just that msxdos2 was introduced in 1988 or 1989. Any machines from before that time obviously only could have built in msxdos1 diskrom. Any machine from a later date could have a built in msxdos2 diskrom. In fact the Turbo R has it.

So Turbo R doesn't need an external cartridge to run msxdos2. It has it internally.

Van Grauw

Ascended (10602)

afbeelding van Grauw

03-03-2022, 11:12

PingPong wrote:

i mean something like the VDP or PSG. msx computers must have a VDP compatibile hw chip.
For disk drives there is no such kind of spec. (for example a specific FDC controller)

Right. The MSX standard just defines the BIOS which gives hardware makers the freedom to choose between any competing chip. This is also the reason why from an MSX software perspective hard drives are accessed the same way as disk drives. On other systems that do use a specific FDC controller and access it directly, it was difficult to introduce HDD support later in their lifecycle.

Most of the MSX standard is defined in this way. That’s why almost all standardised hardware includes a BIOS ROM, and should officially be accessed through it. In practice, for many things manufacturers in practice often used the same chips and I/O ports. For example, in principle you could replace the PPI keyboard interface with a serial PS/2 one, and everything continues to work thanks to the standardised BIOS. But because there exists software that does not use the BIOS to access the keyboard, today it is no longer practically possible to attach a non-PPI keyboard without losing a portion of software support.

Van gdx

Enlighted (5572)

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03-03-2022, 16:35

In the first version, the MSX standard strongly advised to go through the main BIOS and those of the peripherals only, but ASCII relaxed the rules gradually for several reasons including some design flaws in the system that were difficult to fix and the need for speed to make certain things. I think there also were ideological differences to make the compatiblility by hardware or by software. We've had a mix up in following versions moving more and more towards compatible hardware.

Van Grauw

Ascended (10602)

afbeelding van Grauw

03-03-2022, 23:17

The only two exceptions I am aware of are:

  1. The VDP, for the sake of game performance, but you still should read the I/O ports from the BIOS.
  2. MSX-MIDI, which is I/O only. Afaik the ROM contains a BASIC extension only, no BIOS.

What else?

Note I’m not meaning to tell anyone that they can’t access hardware directly in this day and age, just how I see what ASCII’s design philosophy was. I consistently see them applying a BIOS, to MSX-AUDIO, MSX-MUSIC, MSX-RS232, MSX-DOS, etc.

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