ECB Gide - IDE Interface for Z80 ECB Systems

Sometime in the first quarter of 2006 i tried to recover my old Prof80 CP/M Z80 System. After i had the system up ad running from floppy disk i thought about adding a harddisk to it. Till Rehmann designed an universal ide interface for Z80 systems. It was implemented as an adapter that fits into a z80 cpu socket but i wanted to have a card for the ecb bus. The original design used pal's but i dont have a programmer for pals. I found another implementation where the original schematic was used to program a xilinx cpld (9572). I thought i could use this one without modifications but it did not work for me, the access to the 16 bit data of the ide disk was not working.

Ok, why not implementing the stuff in vhdl ? I never worked with vhdl before but the language did not look very complicated. After some evenings i had the first code that worked fine in the emulator and i tried it on real hardware. It worked, but only sometimes. Up to now, i dont really understand it. With help from vhdl gurus on mikrokontroller.net i got tips that spikes may produce this behavior, after inserting some latches it finally worked with tillmanns ide test program written in turbo pascal. (VHDL Source for viewing or Download)

The next step was writing a CPM3 bios and a loader. I decided to use some kind of partition table and a master table on the disk. The master boot record contains the boot code, data about the disk geometry and a partition table. The first sector of the disk is read without initializing the disk to a specific geometry, hope that this works with all disks (i tried 2 or 3 drives and it worked).

Structure of the first sector

The table may contain up to 16 CPM partitions. To allow accessing the first 4 partitions from linux, there are compat fields but they are not yet filled. I wrote a simple fdisk in pascal that can create the partition structure.

The boot process works as follows:

• Monitor loads the first sector to F000h and jumps to the loaded code
• MBR code initializes the drive geometry and checks what partition should be used for boot
• The CPM loader will be loaded to 2100h beginning with the second sector of a partition
• The loader gets started with a jump to 2100h and this will load cpm3.sys

The first sector of a partition contains the disk format and the cpm loader sits after this table:

As you can see, this is the dpb used by cpm3. The ide bios sets the dpb from this table when the login function is called from cpm. There are some maximums that can be set, see ide.z80 for details. Btw, i converted most of the files to z80 and i'm using the slr assembler. Currently i'm using the loader from DR, i also tried ZPM3LDR but it did not work ?

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