Disc Transfer

 

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ADFS Explorer now has the facilities for sending or receiving disc images to your BBC computer.

This feature requires a serial cable to connect your Mac to your BBC computer. Instructions for making up a serial cable can be found here.

The disc transfer features are based on the XFER 5.1 program but only has the facilities (at the moment) for sending or receiving complete disc images and not individual files.

However, a big advantage over XFER is that RLE compression is now used when transferring the data.

RLE compression works by counting the number of consecutive characters of the same value and sending a special count/byte sequence rather than the individual bytes.

You will see major benefits from RLE compression if your disc only contains a few files or lots of blank sectors.

If you have a disc full of random machine code files then you won't see much increase in transfer speeds.

I did try LZH compression but it took longer to compress the data than to actually send it so this was no use.

To use the disc transfer features, you need to make up a serial cable and connect it between your Mac and BBC computer.

In ADFS Explorer, there is a new menu called ADFS Xfer with several options.

You need to first of all tell ADFS Explorer which serial port you are using and what baud rate you wish to use for the transfer. A higher baud rate will of course mean quicker transfers but if you have a slow computer or are using the computer for something else whilst a transfer is in progress, you may notice some retries or CRC errors on the transfer screen due to lost data. A slower baud rate should improve in this situation.

Secondly, you need to transfer a small BBC Basic over to your BBC which acts as a server program for sending/receiving the disc images.

Select Send Basic Program off the menu and follow the instructions given on the dialog box.

If you get problems at this point and cannot get the program across, check out your serial cable connections.

Once you have the program on your BBC, save it away to disc somewhere, then fire it up !

The ADFS Xfer menu contains two sub-menus for sending or receiving disc images and two sub-menus for sending or receiving data images. A disc image is an exact sector by sector copy of the entire disc surface whereas a data image only transfers used sectors. A data image will therefore be much quicker if you don't have many files on your disc.

Pick the BBC drive you want to use. If you have a hard drive fitted, you can backup/restore your hard drive by selecting drive 0 or 1.

After picking the ADFS disc type, you will be asked for a Mac filename containing the disc image to send or asking for the name to call the received disc image.

Once this is all entered, the disc transfer will commence. A progress bar will be shown on screen so you can see how the transfer is proceeding.

Once the disc is transferred, you can then load it into ADFS Explorer to view the contents or run the software on your BBC as appropriate.

If things don't go to plan, another option on the ADFS Xfer menu called Trace will allow you to open a window to monitor the transfer process. You can also capture this information to disc so if you get problems, you can send me the trace file so I can help you work out where any problems may lie.

A further option is also available on the ADFS Xfer menu called 'Check Before Transfer'. Enabling this option will perform a CRC check on the source and destination data before transferring it. If the CRC's match, the data will be skipped. If you already have a disc image available and want to update it to match your BBC's disc, enabling this option will therefore only transfer data which has changed and should yield a much faster transfer rate than simply sending this disc image again. This option could also be used to verify that a source and destination disc image match.

This is the first implementation of disc image transfer in ADFS Explorer but it appears to work OK on my setup here.

Please ensure you have backup copies of your ADFS discs before attempting to transfer them (just in case !)

Future versions may well incorporate some bufffer techniques at the BBC end to speed things up even further. Some time is being lost at the moment whilst the disc continually spins up to speed before reading/writing tracks. I should be able to improve on this by using sideways RAM or main memory to read multiple tracks at once which will improve on this issue.

As usual, if you get any problems or have suggestions to improve on this new feature, please let me know personally.


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Copyright 2006 Jon Welch
Last modified: 17-08-2010