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