ruud.baltissen_at_abp.nl
Date: 2008-01-30 12:30:40
Hallo allemaal,
In the next text you'll find info I'm sure you already know but to save
some time I use the text that I just placed on comp.sys.cbm and
VIC20-Denial.
Question: does anyone know of speedloaders not calling 1541 routines or
addressing the 1541 hardware directly?
I want to present 1541IDE8 V0.4. This is phase 4 in a project where at
the end I should be able to handle IDE hard drives (HD) up to 128 GB
using a 1541 as base. A problem is that the original File System (FS) of
the 1541 only can handle 170 KB disks. Using the BAM technology of a
8250 we can screw this number up to about 16 MB. Replacing the two-bytes
Track/Sector link by a four-bytes LBA link, we can handle drives up to
one TeraByte!
At http://www.baltissen.org/newhtm/1541ide8.htm you'll find the more
technical details including schematics and a picture of my home brew
interface. For the rest the page is a bit outdated but I'm working on
it, therefore this update.
Remark: at this moment I'm using an 8-bits interface and therefore only
using half of the capacity of an HD. So if I mention a 128 GB HD like
above, only 64 GB of it can be used.
What does phase 4?
Phase 4 can handle multiple D64 images. At startup the 1541 will use
image 0 to start with. With OPEN 1,8,15,"Z:xxxxx" : CLOSE 1 (or
@Z:xxxxx) you can change the image. 'xxxxx' is the number of the image
from 0 (zero) up to 12271. But before you can use the drive you have to
format it using the command OPEN 1,8,15,"Y" : CLOSE 1 (or @Y). This
command will fill the image directory and the BAM sector of every
available image with zeros.
I don't 'format' the other sectors. Doing the above for a 4 GB HD will
already take about 2 minutes. Formatting all sectors would cost about 7
hours (I think). But before you can use an image at all, you have to
format it anyway using the well known OPEN 1,8,15,"N:<name>,<id>" :
CLOSE 1 (or @Z:<name>,<id>) and then all sectors are filled with zeros.
An image occupies 768 sectors. These are the original 683 sectors plus
five extra tracks of 17 sectors each as used in various 40-tracks FS's.
These extra 5 tracks are NOT formatted as the original FS has no
knowledge of them.
When formatting an image, an entry is made in the image directory. This
directory occupies (a multiple of) 768 sectors, good for 12788 entries.
As IDE starts counting from sector 1, the first 768 are in fact only 767
sectors, therefore the number 12271 you have read above.
The image directory can be shown using OPEN 1,8,15,"$$" : CLOSE 1 (or
@$$). It will show the number and disk header of the available images.
Remark: I have no idea what will happen if the listing exceeds the
maximum size of a BASIC program. As JiffyDOS outputs a directory listing
direct to screen, it shouldn't be a problem IMHO. But how a standard C64
will act, I have no idea (overflow error ???).
Files:
http://www.baltissen.org/files/idejd4.asm - source code
http://www.baltissen.org/files/idejd4.bin - 32 KB binary
http://www.baltissen.org/files/mp-asm.exe - my own assembler
I use an AT29C256 EEPROM, therefore the size of 32 KB. Sorry, I just
realised it when writing this. Use DEBUG or another program to cut off
the first 16 KB as you only need the second 16 KB for a 27128 EPROM.
Another option is using a 27256 or equivalent.
The number of images an HD can support is hardcoded for the moment and
can be found at $F69E, $002FF0 = 12272 (label CSubIma in the source
code). At $E7B5 you'll find how many clusters of 256 sectors are
reserved for the image directory. At this moment that is 3. This number
MUST be a multiple of 3. 768 sectors are good foor 12280 entries or 4.8
GB. So if you use a 6.2 GB HD this number must be 6 and the number at
$F69E about 18000. During the format of the whole disk I check if a BAM
sector can be written and you'll get a fashing LED if things go wrong
but no info WHERE it goes wrong (for the moment).
Compatibility:
The only speedloader I'm sure of that 1541IDE8 V0.4 supports is
JiffyDOS. Speedloaders that address the floppy drive directly, like FC3,
you can forget now and in the futere. Speedloaders that only call some
routines of the 1541 ROM still make a chance but that is something for
the future. Speedloaders not calling 1541 routines should work but I
don't know of any so I have no proof.
Parallel loaders:
Can 1541IDE8 work with parallel loaders like SpeedDOS and Dolphin DOS?
The answer is simple: I dont know. But IMHO, just get the source code
(in the worst case disassemble the original binaries), combine it with
my source and see for youself.
Remark:
I have two 7-segments LED displays for debugging purposes coupled to the
free A-port of one of the 6522, the one normally used for parallel
loading. If you really want to experiment with parallel loading, look
for and remove everything that has the label 'POSTcode'.
Have fun !!!
--
___
/ __|__
/ / |_/ Groetjes, Ruud
\ \__|_\
\___| URL: Ruud.C64.org
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