> On Sep 21, 2015, at 10:52 AM, Johnny Billquist <[email protected]> wrote:
>
> ...
>>> I've tried to boot an RX01 Floppy in RX02 mode, that failed on all disks
>>> I've tried. Is an original RX02 able to boot (RT11) from an RX01 disk?
>>
>> As far as I know, it can't. An RX02 can read/write an RX01 disk, but the
>> software
>> interface to the controller is so different (the RX)2 uses DMA, the RX01
>> doesn't for
>> one thing) that the RX02 cannot boot an RX01 disk.
>
> Of course an RX02 *drive* can read an RX01 *floppy*. And yes, a system with
> an RX211 and an RX02 *drive* can boot from a floppy that what written by an
> RX01 *drive*. But you need the boot code for an RX211 controller, and that
> boot code also needs to handle RX01 format floppies. If the boot sector on
> the floppy is for an RX11, then no, an RX211 will not understand things. The
> programming model for the two controllers are different. You need different
> device drivers.
>
> But this is really a question about the controller and the software running
> it, not the floppy or the drive.
And it would certainly be possible to write a driver that can handle both
controllers; it would start by determining which controller it's dealing with,
and then run the one or the other set of algorithms. Since a boot block is
just a small driver, the same is true there, so long as the whole body of code
fits in the available space. I suspect in this case that's doable; most
bootloaders (other than MSCP ones) require only a small fraction of the
available space.
paul
