aliu@nunki.usc.edu (Alejandro Liu) (02/16/89)
One simple and unsophisticated (therefore, not that dramatic) approach
to the speed-up problem is by using the 1541 fast mode. I remember
that the VIC-20 could make serial transfers 25% faster than the C-64,
that's why C-64's had such a hard time reading the old 1540 drives.
People who had VIC-20's could take advantage of this extra speed by
sending the user command 'uj' to the disk (I am not 100% percent sure
about this, I don't have my Disk Manual handy, but I think is fairly
common thing)
Anyway, a simple but easy way to speed up ALL disk operations is to
send this command to the disk drive, to put it at VIC-20 speed. That
will make the 1541 run 25% faster. Normally, the C-64 will have a
hard time coping with this extra speed. The way to put the C-64 at
the same speed without great programming feast, is by simply blanking
the screen. (Blanking the screen, produces the C-64 to run 25%
faster, because the Video Chip doesn't need to access the memory any
more). Therefore, everytime one wants to perform a disk access, one
simply blanks the screen, and enjoy a humble 25% improvement in the
speed. (I actually tested this on LOAD and SAVE, and works. File
operations didn't improve at all because I was using BASIC, and
Commodore BASIC is slow enough that the Drive is still faster that the
interpreted BASIC)
--
aliu@nunki.usc.edu (Alejandro Liu)
(Simple .signature, $CHEAP$) fred@cbmvax.UUCP (Fred Bowen) (02/17/89)
In article <2719@nunki.usc.edu> aliu@nunki.usc.edu writes: >One simple and unsophisticated (therefore, not that dramatic) approach >to the speed-up problem is by using the 1541 fast mode. I remember >that the VIC-20 could make serial transfers 25% faster than the C-64, >that's why C-64's had such a hard time reading the old 1540 drives. >People who had VIC-20's could take advantage of this extra speed by >sending the user command 'uj' to the disk (I am not 100% percent sure >about this, I don't have my Disk Manual handy, but I think is fairly The command is UI- to remove a 40us delay per bit, imposed to cope with VIC-II DMA's. As you indicated, blanking the VIC screen (POKE53265,PEEK(53265)AND239) or placing a C128 in FAST mode stops VIC DMA's and so this delay can be removed. The command UI+ re-imposes the delay. So, like the C64's MAX mode, the 1541 has a 1540 mode. Guess that makes the C128D something like, um, 7 machines in one? The extremes to which we go in the name of compatibility boggles the mind, doesn't it? -- -- Fred Bowen uucp: {uunet|rutgers|pyramid}!cbmvax!fred arpa: cbmvax!fred@uunet.uu.net tele: 215 431-9100 Commodore Electronics, Ltd., 1200 Wilson Drive, West Chester, PA, 19380