The dual drives do it with a separate gcr rom. Look for that on my petindex site http://www.6502.org/users/andre/petindex (sorry, only on mobile device right now) André Gesendet mit AquaMail für Android http://www.aqua-mail.com Am 13. Januar 2013 17:47:10 schrieb Gerrit Heitsch <firstname.lastname@example.org>: > On 01/13/2013 05:27 PM, email@example.com wrote: > > > > On 2013-01-13, at 07:30, Groepaz wrote: > > > >>> Is there anything known that would be still faster? AFAIU ProfessionalDOS > >>> does it faster but with help from its hardware. Anyone heard of faster > >>> than 1571 but pure software based decoding? > >> > >> thats basically just an eprom with an huge lookup table though (the cbm dual > >> drives do it in a similar way) > > > > Like putting bits on address lines and reading the outcome from data > lines? It could be an option, depending on how "huge" the table has to > be... It can't be 40 bits so some bit fiddling has to be done anyway. > > > > Also I found a post by Jim Drew on Lemon64, where he admitted to have > decoded GCR in real time thanks to extra RAM on the SC+ card and > "creative tables". Since he's got "only" 8K of extra RAM, he had a hard > limit on the size of the table. If I fit into 8K and have GCR decoded > in RT I can't have any more wishes ;-) How is it done in dual drives? > > I thought GCR is a 10/8 encoding, meaning you get 10 Bits off the disk > which translate to 8 Bits. That would mean you need a 1 KByte table to > do decoding full bytes by lookup table. > > If you do it by nibble, you need a table with 32 entries. > > Gerrit > > > > Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2013-01-13 21:00:02
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