Boot ROM source

This package contains my boot ROM source. Its a fork of the official code developed back in the late 1980s. It has the following features/enhancements :-

• Supports the use of the 80 column card, or the VDP chip in a crude 56 column mode (aka "SCPM" mode).
• Supports FDX disc controller, SDX disc controller, or ROM disc controller.
• Supports booting from RAM Disc, if it looks like it contains CP/M.
• Supports RAM Disc types 50, 51 and the recently invented 52.
• Supports initialising RAM Disc from a ROM card, if RAM Disc doesn't contain what looks like CP/M (aka "RCPM" mode).
• The boot drive/type order can be configured.
• The boot ROM turns off the sound on startup.
• Pressing both Shift keys during startup prevents booting CP/M.
• Ability to download Intel Hex files.
• Remote Command mode.

Source for CONFIG.COM and SIDISC.COM is included also, as this understands the new type 52 RAM Disc. It should be noted that RECONFIG.COM in REMEMOTECH and REMEMOrizer is a superset of this, and also supports SD Cards, and provides better error messages.

Usage

The boot ROM signs on, performs a memory test, and then tries to boot from various drives of various types, such as drive B of type 07 :-

MTX Bootstrap Prom #@SDX03-V03

Ram Test - OK

Boot B07

Ordinarily a boot ROM for a given system will have a boot drive sequence suitable for it. eg: if the system has RAM Disc, it will be set up to try F51 or F52 before any of the floppy disks.

If you hold down Enter during the Ram Test, you get a > prompt, where you can use these commands :-

• B<drive><type> - Boot from drive of given type, eg: BC07
• S<addr> - Show and Substitute, ie: display and edit memory at address. Type new hex values to change bytes. Space advances to next byte without editing. Down arrow moves to next row of 16 bytes. Return exits back to the prompt. eg: S8000
• G<addr> - Goto address. eg: G0100
• D - Dialog. Initialises RS232 B to 19200,N,8,2 and behaves as a crude terminal until ^Q is typed to exit the mode. MTX serial port B is wired as a DTE. Use this to prove the serial cable connecting to a DCE or null modem cable connecting to another DTE is working.
• R - Read. Initialises RS232 B to 19200,N,8,2 and then downloads data in a subset of Intel Hex format. This should be a set of type 000H data records followed by a single type 001H End-of-file record. The address in the End-of-file record should be where execution should start from. If the data received is invalid, it returns to the prompt. Note however that not many data validity checks are performed. In this scenario you'll be using a null modem cable because both the MTX serial port B and the PC sending data to it are wired as a DTE. Where "SCPM" screen mode is used, it is necessary for the sender to pause sending when it knows the screen will scroll (as this is very slow) causing loss of data - this is only an issue for downloads over 35KB.
• C - Remote Command mode. Initialises RS232 B to 19200,N,8,2. Receives commands over RS232 allowing a remote host to do I/O, read/write memory and execute code.

The boot ROM copies itself to 0E000H and above, and its stack will be at 0E000H growing downwards. If experimenting with the S and R commands, best to leave memory above DF00 alone.

Earlier versions of this code didn't initialise the RS232 settings properly, so D and R commands didn't work. I am not sure if the original FDX boot ROM code (or the SM1 boot ROM code before it) had the same problem.

The Remote Command mode is an optional enhancement over the functionality of the original boot ROM code. See the ZMON Remote Command mode tool to understand how to use this feature.

The MTX has real RS232, at 12V levels. Modern PCs don't seem to come with RS232 ports any more, so its quite common to use a USB to RS232 converter, and these are dead cheap on eBay. However, many of these are USB to RS232 TTL (ie: 5V levels). As I'm not confident the MTX would work if only fed 5V, or whether these cheap converters would tolerate 12V from the MTX, I have bought and successfully used a CHIPI-X converter, which has the FTDI chipset and converts voltages.

Building

Code is supplied with a Linux makefile, which makes it possible to compile the various ROMs using MEMU, M80 and L80.

Customisation is a combination of EQUates specified in the assembler source file, called BOOTCONF.INC.

To reproduce the BOOT ROM I used in my fully-loaded FDX system, which had 512KB extra RAM, 2x 8" drives and 2x 5.25" drives, use a file starting like this :-

;
; BOOT ROM configuration
;

; One of these must be selected
CRT80	EQU	1
CRT56	EQU	0

; One of these must be selected
FDXFDC	EQU	1
SDXFDC	EQU	0
ROMFDC	EQU	0

; This can be selected
ISIDISC	EQU	1

; This can be selected
ROMPAIR	EQU	0

; This can be selected
REMCMD	EQU	1

; At least one of these must be selected
BOOTF50	EQU	0
BOOTF51	EQU	1
BOOTF52	EQU	0
BOOTD13	EQU	1
BOOTE13	EQU	1
BOOTB07	EQU	0
BOOTB03	EQU	1
BOOTC07	EQU	0
BOOTC03	EQU	1

; This can be selected
INITF	EQU	0

; Set system type
STYPE1	EQU	'F'
STYPE2	EQU	'D'
STYPE3	EQU	'X'

Immediately after these EQUates are a set of checks designed to spot when the user chooses illegal combinations.

Sensible combinations :-

• only use 3.5" or 5.25" types if FDX, SDX or ROM FDC
• only use 8" types if FDX FDC
• only use RAM Disc types if Silicon disc handler installed
• only try to initialise RAM Disc if RAM Disc type is selected

Some examples :-

• FDX - CRT80,FDXFDC,BOOTB03,BOOTC03
• My fully-loaded FDX - CRT80,FDXFDC,ISIDISC,BOOTF51,BOOTD13,BOOTE13,BOOTB03,BOOTC03
• Older SDX - CRT80,SDXFDC,BOOTB03
• Modern SDX with extra 512KB RAM - CRT80,SDXFDC,ISIDISC,BOOTF51,BOOTB07
• Videowall MTX - CRT56,SDXFDC,ISIDISC,BOOTF51,BOOTB07
• Videowall SDX with ROM card - CRT56,SDXFDC,ISIDISC,BOOTF51,BOOTB07,INITF
• A better Videowall MTX with 128KB ROM card acting as ROM Disc - CRT56,ROMFDC,BOOTB03
• A better Videowall MTX with 2x128KB ROM cards acting as ROM Disc - CRT56,ROMFDC,ROMPAIR,BOOTB03
• My one-off SDX+ - CRT56,SDXFDC,ISIDISC,BOOTF52,BOOTB07
• My older SDX - CRT80,SDXFDC,BOOTB03

After building, the result is BOOT.BIN.

Installing

The FDX User Manual includes the circuit diagram for the FDX bus interface card. This is the card that usually contains the boot ROM.

The card has 3 link settings, supporting various chip types :-

• a - TMS2564
• b - TMS25128 (ie: like a TMS2564, but twice as big, if such a thing exists)
• c - 27128 or 2764

Odds are you'll be able to most easily source 2764 or 27128, or something pin compatible with it, such as an W27C512 EEPROM. So hope that your links are set to position c. If you source something bigger, just repeat the content. eg: repeat 8KB 8 times to fill 64KB W27C512.

In the circuit diagram, A13 is fed to the socket, which is pointless. In order for the chip to be selected, A15-A13 must be 001. If R0 can be rewired in place of A13, and a 16KB device installed, then the socket can host one 8KB image for ROM slot 4 (the CP/M boot ROM) and another 8KB image for ROM slot 5 (a SDX BASIC ROM).

Older SDXs will only accept 8KB EPROMs. Later SDXs will accept 16KB EPROMs, which should contain the CP/M boot ROM in the bottom 8KB and SDX BASIC ROM in the top 8KB. I have successfully used W27C512s in place of a 27128 in my later style SDX.

Memory map

High memory looks like this :-

Address	Content
0EC00H	SIDISC, if installed
0F000H	KBD
0F300H	DBUF (used by DISC / FDSC)
0F400H	CRT / SCRT
0F980H	TDBUF (used by DISC / FDSC / ROMD)
0FA00H	DISC / FDSC

CP/M CBIOS and certain user programs usually use the drivers through vectors installed very high in memory.

However, be advised that certain programs are known to look directly inside the CRT handler code, and even call directly into it (eg: VDEB.COM).

Silicon and RAM Disc support

Memory above 0F000H is where the CP/M boot ROM installs itself to. The boot ROM source presented here can also load the Silicon Disc and RAM Disc drivers below 0F000H, in much the same way that the SIDISC.COM program does. Because of its ability to do this, it becomes possible to boot from RAM Disc. At this time, its not possible to boot from Silicon Disc, primarily because the code doesn't include a mechanism to test whether Silicon Disc contains what looks like CP/M. This could be revisited, should the need arise.

Shrunken type 51 RAM Discs

If using a 512KB RAM disk card, then there was 512KB of memory for the F:51. If using series 2 MTX, or MTX 2000, then the RAM disk size had to be shrunk, using S2R.COM or similar programs. Different type codes for new smaller sizes of RAM Disc would have been better.

56 column VDP support

ROMs with this feature are known as "SCPM" ROMs.

This feature was developed to provide a cheap way for SDX owners to run CP/M, without having to need an 80 columm card. It was particularly useful for Video Wall Controllers, where although the system booted using CP/M, it would go directly into the Video Wall program, which used the VDP. There was no real requirement for the 80 column card.

The SCRT screen driver has some limitations compared to the normal 80 column card CRT screen driver :-

• The new CRT module has only 56 columns.
• The DOT and VCT control codes are not installed, as are any block graphics.
• Neither the cursor or any characters flash.
• Write masks are ignored and so are print control attribute bytes (ESC-W,P,N,B). No known software uses these control codes and no new ones are expected to.
• Colour is per 2 thin characters only.
• Certain CP/M programs may use the VDP screen and after they finish the screen will probably be corrupt. However a CLR reinitialises part of the VDP. It does not re-install the character set. If this is lost you may recover it by using the SCH.COM program.

Two extra escape codes have been provided:-

Code	Action
^[Q	Disables all colour update of the screen. Colour control codes are not ignored but merely do not affect the screen. This will result in slightly FASTER screen update.
^[R	Re-enables colour update of the screen. Any colour changes that may have occured before will now become apparent.

Both these codes perform a screen CLR. These control codes have NO EFFECT on an 80-col card.

Programs that won`t work :-

• VDEB.COM Written for 80 column screen size. Directly looks and calls inside CRT handler. Use ZSID.COM instead.
• FDXB.COM. Written for 80-col card. Use MTX, MBASIC or BBCBASIC.
• WS.COM. Cannot be patched for screen width of 56, use N56.COM. Note: N56.COM is not the latest NewWord, but it as version that does not try to patch the keyboard low-level drivers.
• CONTACT.COM. Writes directly to the 80-col card hardware It is possible to patch CONTACT to use the new SCRT module, although this has not yet been done.
• COLDBOOT.COM - uses boot ROM !

Initialising RAM Disc from ROM card

ROMs with this feature are known as "RCPM" ROMs.

This was a feature developed to allow Videowall Controllers to be shipped with a ROM card instead of a SDX disk drive. The ROM card would contain the RCPM ROM and the initial RAM Disc. When the system boots, it would spot the RAM Disc is unitialised and initialise it from sub-pages of the ROM card.

Sub-page 0 contained the RCPM CP/M boot ROM (compiled with CRT56,SDXFDC,ISIDISC,BOOTF51,BOOTB07,INITF). Sub-pages 1-15 contain the initial RAM Disc image.

To prepare the ROM images :-

• FORMAT F:
• SYSCOPY F:
• Copy the files onto F:
• STAT F:*.* to see how much space is used
• add 8KB to allow for directory space
• divide by 8KB, rounding up, to give the number of ROM files (note: sometimes, it may be necessary to add one)
• RCPMGEN name number_of_ROM_files+1
• Use files BOOT.BIN, name1.ROM, name2.ROM, ... etc. to blow the EPROMs.

As an example, to create a boot from ROM system for the Video Wall program (VW6.COM) and video wall program sequences for Top Shop (DEMO.VW and OTHER.VW), use the following commands :-

B:
CONFIG F:51
FORMAT F:
SYSCOPY F:
F:
STARTUP S2R\VW6 F8\\F3\\F1\\"DEMO"\\F8\\F4
B:
PIP F:=C:VW6.COM
PIP F:=C:*.VW
PIP F:=B:S2R.COM
STAT F:*.*                    (total disc space <= 72KB say)
                              (add 8K for directory = 80KB)
                              (divide by 8K gives 10)
                              (add one just in case)
RCPMGEN C:TOPSHOP 11

This gives 12 .ROM files altogether (including the "just in case" one). That gives 3 32KB EPROMs, so we might as program the "just in case" .ROM file anyway.

When the newly produced system boots, the following should occur :-

A>S2R
A>VW6 F8\F3\F1\"DEMO"\F8\F4

If you have a 128KB EPROM board modified to hold 32KB RAM chips then you can use the utility EP.COM to "blow" the RAMs. Type :-

EP filename.ROM sub-page_number

It copies the 8KB file "filename.ROM" into ROM 2 at sub-page "sub-page_number", and verifys that copying went ok. When you have used EP on all of the .ROM files then just reset. This should prevent blowing EPROMs that wont work.

ROM Disc

Recently, the ROMFDC option has been added, and this provides a much better alternative to initialising RAM Disc from ROM. Instead of copying R/O content to R/W RAM Disc and then usually not modifying the result, simply run directly from ROM Disc. No RAM Disc is required, and we can benefit from compression.

Disk to ROM explains how to make the disk image.

MTX ROM Card is a simple and large ROM Card.

Download

Full package downloadable from here.