ROM contents and tools of the Floppy-Speeder Professional-DOS, Version 1

As with many other floppy speeders for the C64 and C1541, the Kernal ROM of the C64 and the DOS ROM of the C1541 needs to be replaced for Professional-DOS.

Firmware and tools download

Professional-DOS, Version 1 ROM files (28kB): ZIP-File with all the ROMs and tools discussed here in raw binary format. Each of the ROMs does not contain the typical CBM style load addresses at the beginning of the file (except for program files ending with .prg). They are meant for professional EPROM burners or Flash programmers (PC based).
Professional-DOS, Version 1 Kernal files (25kB): ZIP-Compressed D64 disk image with all the ROMs and tools discussed here in typical CBM style format. They are meant for direct use with eprom burners for the C64.

C64 Kernal ROM

With the first versions of Professional-DOS, many users got the ability to modify existing speeder firmware with a special ROM patch utility to create a C64 Kernal ROM their own. This way the user didn't need to learn other command sets, but could the already known of the old speeder.
For the Professional-DOS version presented here the C64 Kernal was missing since it arrived, but one patch utitlity could be found, that creates a Kernal out of an existing SpeedDOS floppy speeder system. This way a C64 Kernal for Professional-DOS Version 1 could be created. You can find this utility as well as the ready built C64 Kernal ROM in a ZIP archive below.

C1541 DOS ROM

The EPROM of the drive expansion board doesn't not only contain the drive replacement ROM located in the C1541 memory map from 0xe000 to 0xffff. It also contains additional ROM code, that is mapped to the memory location 0x8000-0x9fff (this is only valid for Version 1). The floppy ROM located from 0xc000 to 0xdfff remains untouched.
When you insert the drive expansion board, you have to remove the main (upper) DOS ROM as the manual says, because the replacement ROM is already supplied with the board. Some logic of the board splits the 16KB EPROM (27128) into two parts and maps each half to another memory location of the drive's memory map. The EPROM adresses from 0x0000 to 0x1fff are mapped onto the drive's addresses from 0xe000 to 0xffff. EPROM adresses from 0x2000 to 0x3fff are mapped to the drive's addresses 0x8000 to 0x9fff.
The ROM code, that has been added mainly contains fast GCR decoding routines as well as some big decoding tables. But these routines will not work without the special hardware extensions given by the drive expansion board. As far as the GCR decoding process could be revealed until now, the decoding routines only select the right table. The hardware does the whole rest: splitting a byte into nibbles, decoding each nibble with the help of the big GCR tables and storing the result into RAM. All you can see (if you disassemble the ROM) are many consecutive LDA and ORA instructions, that make no sense under normal circumstances, e.g.:

902f 50 fe bvc $902f 9031 b8 clv 9032 ae 01 1c ldx $1c01 9035 bd 00 81 lda $8100,x 9038 bd 00 80 lda $8000,x 903b 50 fe bvc $903b 903d b8 clv 903e ae 01 1c ldx $1c01 9041 1d 00 83 ora $8300,x 9044 c5 39 cmp $39 9046 f0 03 beq $904b 9048 4c 7b 91 jmp $917b 904b bd 00 84 lda $8400,x 904e 50 fe bvc $904e 9050 b8 clv 9051 ae 01 1c ldx $1c01 9054 1d 00 87 ora $8700,x 9057 85 1a sta $1a 9059 bd 00 80 lda $8000,x 905c 50 fe bvc $905c 905e b8 clv 905f ae 01 1c ldx $1c01 9062 bd 00 81 lda $8100,x 9065 1d 00 82 ora $8200,x 9068 85 19 sta $19 906a 45 1a eor $1a 906c 85 1a sta $1a 906e 50 fe bvc $906e 9070 b8 clv

C1541 additional RAM

The drive expansion board also brings an additional 8K static RAM into the drive's memory map. This 8K RAM is located at the addresses from 0xa000 to 0xbfff. Take note, that this is only valid for Version 1 of Professional-DOS. Later revisions mapped the extra ROM and RAM into the address space from 0x4000 to 0x7fff.

Wolfgang Moser, 2002-09-25