P112 Frequently Asked Questions


Q: Does the GIDE operate as a boot device?
Yes, it does.  The P112 Boot ROM searches the boot chain until it finds a boot device with a properly-formatted Boot Record.  It repeats the search ten times before declaring an error.  If there is not a floppy disk in Floppy A:, and no SCSI device is present, the GIDE will be booted (if present and the boot record is properly formatted.)
Q:  What is the "Boot Chain"?
The Boot Chain sequence is Floppy, SCSI, and then GIDE.  The P112 ROM first attempts to boot the floppy.  If an error occurs (such as no disk in the drive) it will attempt to boot SCSI Unit 0:.  If not found, or it doesn't have a properly-formatted Boot Record, the P112 will attempt to boot from the GIDE.  Again, a properly-formatted Boot Record is required.  BPSYSGEN.COM is used to install the operating system image on the Boot Tracks and format the Boot Record.
Q: Does the GIDE mount directly to the P112?
Yes, but there's a problem: the P112's battery holder is too tall.  The materials supplied with the GIDE adapter kit require that the battery holder be removed and either relocated (laid flat) or replaced with an external battery.  Another option is to mount the GIDE UNDER the P112.  To do so will require that the P112's 3x16 expansion connector be mounted to the BOTTOM of the P112 instead of the top.  Obviously, this has to be done during initial construction.  A photo is available on the photo page for reference.
Q:  After GIDE boot, Floppy A: becomes Drive A: and GIDE Partition 0: is Drive F:.  Why isn't GIDE 0: set as Drive A:?
After using BPSYSGEN to copy the OS to the GIDE system tracks, you must run BPCNFG on GIDE partition 0: to logically re-assign the drives to the desired drive letter.
Q:  How do I re-assign drive letter mapping?
Use the command line BPCNFG ?: (where ?: is GIDE partition 0:) and select menu option 5 - Logical Drive Layouts.  Read the prompts at the bottom of the screen, and swap the logical devices around until you have the logical drive mapping the way you want it.  At the very least, Drive A: should be set as the first GIDE partition.  Exit BPCNFG, allowing it to update the Boot Track system image, and reset the P112 to boot from the GIDE.  Drive A: should now be GIDE partition 0:.  If you're using a banked image for RAM sizes > 64K, you should also assign the same logical mapping to the banked image with a command line such as:
BPCNFG BANKxxxx.IMG   <--- Where 'xxxx' is the size of the image, such as 128K, 256K, 512K, or 1M.
Q: Why does loading a Banked image require a two-stage boot?  Why not boot directly into the banked image?
Quoting from the B/P BIOS manual:
"For most of the existing CP/M-compatible computers to begin executing a Disk Operating System, a program must be placed on a specified area of a Floppy or Hard Disk Drive.  Normally, the first two or three tracks on the disk are reserved for this purpose and are referred to as the "Boot Tracks."  Since the space so defined is generally restricted, neither a complete B/P Bios nor a banked installation is possible.  Instead, a scaled-down system roughly equivalent to those currently in use is used to start the computer and serve as the Operating System, with larger systems loaded later as needed."
Additionally, changes made to the Banked images (size, location, etc.) may also require changes to the Boot ROM.  While not impossible, it would eliminate much of the versatility of having different Banked images available for different applications.
Q: Is it possible to run the P112 with an 18.432MHz Crystal?  Why should I?
Yes.  Mine is running at 18.432MHz and works fine.  You gain two advantages: 1) A slightly faster machine with a 15% decrease in execution time, and 2) slightly more accurate baud rates, particularly important at baud rates above 38K.
Q: What else do I need to do to run my P112 at 18.432MHz?
When running B/P BIOS, certain timing functions are determined by the CPU clock, including baud rates.  The BPCNFG Menu 1 - System Options --> Option 4 allows you to define the system clock speed in MHz, and offers the option of scaling the timer constants.  Select 'Yes' and the Reload/Timer constants will be updated automatically.  MHz are entered in the nearest whole number, so '18' is correct.  To effect this modification, you should first run BPCNFG on both the Boot and Bank images, and then change the clock rate and timer constants.  Shut down the system, replace the crystal, and then power up and boot.
Q: How much memory is 'necessary' for P112 operation?
The P112 ships with 64K of static RAM.  This is sufficient for full operation of the P112 when using the operating system disk supplied with the P112.  However, when running the GIDE adapter, the BIOS is changed to Hal Bower's B/P BIOS, a Banked BIOS, and a fully-configured B/P BIOS requires more memory.  Although a 64K memory map will work with the B/P BIOS, you won't get the full advantage of the Banked OS unless you have Banked memory, i.e., more than 64K.  128K is a minimal configuration for a B/P BIOS implementation without a RamDisk or User Bank.  To enable the RamDisk and User Bank features of the B/P BIOS, you'll need a minimum of 256K of RAM.  This is accomplished by installing two 128K RAMs.  However, a single 512K RAM is cheaper than two 128K RAMs, and provides a much larger RamDisk.  The only advantage to having 1MB of RAM is an even larger RamDisk.  Consequently, 512K RAM is considered the 'standard' RAM for a fully-configured P112 with B/P BIOS and a GIDE adapter board.
Q: Do Compact Flash-IDE adapters work well with the GIDE?
Yes, they work extremely well.  They appear to be slightly faster than a hard drive, run cooler and much quieter, and use far less current.  CF modules DO have a write-cycle limit, but the best information I can find suggests that anywhere from several hundred thousand to millions of write cycles are common before the CF module is 'worn out,' so it should last for a few years in most cases.  Although this photo shows I'm using two 128MB modules, the BIOS partitioning is such that a single 64MB module is sufficient.  Of course, you can easily modify the partition tables to use larger (or smaller) modules if desired.  Either one (Master) or two (Master-Slave) module(s) can be used.  You can also use a CF-IDE adapter as Master (or Slave) and a normal IDE drive as Slave (or Master.)
Q: Can I use the GIDE adapter with my original, Dave Brooks-issued P112?
I don't know - it hasn't been tested, but I can't think of a single reason why it wouldn't.  It WILL require a Boot ROM upgrade to the current ROMv5 software, available on the Services page.  If any 'old' (original) P112 owners want to experiment, special arrangements can be made as a test case.  E-mail this site for additional information.
Q: What capacity IDE drive can I (or should I ) use?
There is no good answer for this.  As configured, the B/P BIOS allows for 5 partitions on a single drive, with a total of 64MB of storage.  These numbers were set as a 'reasonable' estimate of typical usage.  If you want more, you can easily re-configure the BIOS to allow 10 partitions on a single drive.  Each partition can easily have 20MB of storage capacity.  Realistically, I suspect I will never use the full capacity of one 64MB Compact Flash drive.  And I'm running two of them! (The second drive is used only for backup purposes.
As for BIOS limitations, although the BIOS can 'handle' Cylinder, Head, and Sector values for an 8GB drive, it can only address 512MB on a physical drive.
Q:  My CDROM drive faults out and CDZSWP exits every time I try to load a CD.  What's wrong?
There seems to be a timing issue with older CDROM drives.  In essence, I believe the driver 'times out', generates an error, and CDZSWP exits.  By enabling the internal debug code, the driver runs a little slower, and older CD drives that wouldn't work, will then work fine.  Compiled versions are available the make use of the secondary GIDE adapter, for both Master or Slave drives, with and without Debug code included.
Q:  22DISK doesn't work with the P112.  Has something changed?
The original P112 has an entry in the 22DISK diskdef file that worked with the original P112 disk parameters.  However, the 'new' P112 uses slightly different parameters in the diskdef.  The following parameters (with the new values) have been shown to work correctly with 22DISK:
 DSM 710 - Additional System Track means 4 blocks less free space
 DRM 255 - Now has 256 DIR entries, vice 128 in old definition
 AL0 0F0H - DIR Allocation Byte Zero (not 'oh') to reserve 4 blocks for DIR
 OFS 2 - Two System Tracks vice one
Q:  9600 Baud is too slow.  How do I change baud rates on the P112?
The baud rate has to be changed in four different places.  Before you begin, download and RAWRITE a new system disk.  Boot the disk, and run BPCNFG A: from the command line.  This will allow you to change the baud rate used by the Boot BIOS.  Select menu option 2 - I/O Configuration, and then option 2 on the sub-menu.  Select the baud rate you want to use - try 19.2K.  Depending on your terminal, you MIGHT be able to use 38.4K without Flow Control.  When complete, press RETURN twice to save the modified Boot BIOS.  Reset the P112 and press ESC before the boot process begins.  The Configuration menu will be displayed - select option 'D' to change the baud rate stored in the NvRAM.  Select the same baud rate you set for the Boot BIOS.  Press ESC to exit the configuration menu and save the new values.  The P112 will restart, and you'll see garbage on the screen - this is expected, so just ignore it for now.  Next, change the baud rate on your terminal to whatever was selected for the Boot BIOS and the NvRam.  The particulars of how to do this are in your terminal's manual.  All terminals and terminal programs can be changed in one way or another.  When complete, reset the P112.  It should display correctly at the higher baud rate.  Let the system boot into the Boot BIOS, but do not allow it to load a Banked BIOS.  Finally, you must run BPCNFG BANK1M (or whatever memory size image you normally use) and perform the same modification you did earlier to the Boot image.  When complete, you can load the Banked image with LDSYS BANK1M.
When this change is complete and working correctly, you'll need to BPSYSGEN the boot image to all boot disks, and copy the Banked image to the same disks.


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