Using the 14Mhz speedup modification.

If you have performaed the 14Mhz modification and find that you have disk
errors, it is probably because of the track stepping speed having been
altered.
All of the disk read/write operations aren't directly controlled
by the 68000 cpu so our sppedup mod shouldn't affect this. However the
track stepping on the drives is controlled directly by the CPU.
Normally the trackdisk.device uses a value of 0BB8 as a count between it
when it should send step pulses to the drives. At high speed the time taken
for the count will diminish, in some cases to a point where the step pulses
are sent to the drive quicker than it's track to track access time which
could be around 20ms.While using an 80track 5 1/4" drive with a 5ms track
time there is no problem whatsoever, however with the internal drive on some
machines they cannot keep up with the cpu.

The fix is relatively simple however.

If you are booting from a hard disk such as the A590 include the program
SPEEDUP from this disk as part of your startup sequence.
for example   -  SPEEDUP FFF   -   this will change the delay value from
BB8 to FFF which should be sufficient for most drives. if not just increase
the value till the read/write errors dissapear.
For drive df1: use  SPEEDUP df1: fff

If you are booting from floppy the procedure is a little more complicated.

The easiest way is to add some code to the boot sector to directly patch
the trackdisk.device code.

When the machine is booting a series of vectors and values associated with
trackdisk.device are loaded into RAM. On a 1meg Amiga with no hard disk or
other auto-configuring device connected the location for the trackstep
coundown value is loaded to $C0475E.
All that has to be done is to modify this location during execution of the
boot block code to our new count of $FFF.
This location will differ for other configurations. Use ROMCRACK or some
such thing to find the absolute location in memory for your particular
system.

Examine the bootblock code on this disk in the file TRAKBOOT
Dissassemble it and you will find the assembler instruction:

	move.w    #$0FFF,$c0475e

This bootblock can be installed on any of your normal DOS disks to allow
the speedup mod to operate correctly.It will however only work on a 1meg
amiga with no axpansion memory or hard drive. With the hard drive however
you can use the speedup program in your startup on the HARD disk as
previously described.
I am using kickstart 1.3 so this memory location may vary with other
kickstart versions.

Alternatively if you don't have the the trakboot file with this doco,
modify your boot block to the following using a suitable sector editor:

 00: 444F 5300 DE23 CD7F 0000 0370 48E7 FFFE 
 10: 6152 4CDF 7FFF 43FA 0018 4EAE FFA0 4A80
 20: 670A 2040 2068 0016 7000 4E75 70FF 4E75
 30: 646F 732E 6C69 6272 6172 7900 2C78 0004
 40: 207A 001A 227A 001A 93C8 2009 7205 7400
 50: 227C 0000 0000 4EAE FD96 6008 0020 0000
 60: 003F FFFF 33FC 0FFF 00C0 475E 4E75 0000 ---- note the relevant bytes
 70: 0000 03F2 0000 03EB 0000 0001 0000 03F2
 80: 0000 0000 0000 0000 0000 0000 0000 0000
 90: 0000 etc.....

If you find this hardware mod and doco usefull I urge you to send $5 (or
more if you like it that much!) to :
Leslie Ayling P.O. BOX 334 Glebe 2037 Australia
in the spirit of shareware.

 I hope you like the mod.......Regards Leslie Ayling.

p.s. with an A590 with 2megs of ram the location of the countdown value
appears to be $C069EE. so if you want to boot from the floppys (under 1.2
kickstart for example make the appropriate changes).