[Oberon] Emulators

Michael Schierl schierlm at gmx.de
Wed Jul 29 17:04:56 CEST 2020

Hello Wojtek,

Am 29.07.2020 um 14:49 schrieb Skulski, Wojciech:
> Michael:
>   now you got me confused. We had this long discussion concerning image formats. I was asking whether it is possible to modify your emulator to open the original *unpatched* image. From all that you were saying I understood that it is not only possible, but in fact it was done. The only reason to patch the images into the PNG format was that the raw format cannot be served over the web (no support for binary file transfer in IE10), while every web browser will take the PNG.

Yeah, we had that discussion. And I tried to point out that there is a
difference between the format of the image (PNG vs RAW) and the hardware
emulated by the emulator. Seems that I was unable to get the point across.

My JS emulator supports both PNG and RAW images. RAW images are the same
image format as the other emulators use. However, it does not emulate
all of the hardware of the real board, in particular it does not emulate
the SD card conected via SPI (and it does not emulate the PS/2 keyboard,
but that is noticed much later in the boot process). So you need an
image that contains a "driver" for the disk interface emulated by the
emulator. Most images for other emulators do not contain such a driver,
hence the requirement to "patch" such a driver into the image before
using it with my JS emulator.

This is the same as with other hardware. You may be able to attach both
SATA hard disks and USB hard disks to your computer and boot from both.
Yet if you take a hard disk that contains an operating system compiled
with only USB hard disk drivers (no SATA disk drivers) from a USB hard
disk enclosure and attach it via SATA directly, it will  not *boot*,
while it did still boot while in the USB enclosure. You will still be
able to read the disk content fine when booting from another disk, even
when the disk is attached via SATA but the OS on the disk only contains
USB disk drivers.

Analogous if you attach an unmodified image (with original SPI SD disk
driver) to my JS emulator, yet boot it via serial link from another
system that has the correct disk driver, you can access the disk just
fine. (This is left as an exercise to the reader.)



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