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Fundamentals of FOSSIL implementation and use
Draft Version 4 August 10, 1987
Vincent E. Perriello, VEP Software

IFNA Address: Network 141 Node 491 (141/491)
Usenet address: ...decvax!envore!vaxine!spark!141!491!Vince_Perriello

Copyright (C) 1987, VEP Software, Naugatuck, CT 06770. All rights reserved.

This document may be freely used or copied by anyone interested in the data
contained herein. No fees may be charged for distribution of this document.
You will be held accountable for all such charges, and expected to either
reimburse those persons or organizations so charged, or to make a donation
in the exact amount of those fees to the International FidoNet Association,
to assist them in their efforts to advance the technology of personal
computer telecommunications.

Fundamentals of FOSSIL implementation and use Page 1

A. Objectives of this document

This document is directed at implementors or intellectuals. It is meant
for use in implementing applications that can use FOSSIL drivers, or for
details needed to implement a new FOSSIL. As such it won't always go out
of its way to explain itself to the neophyte.

This document will have served its purpose to you if you are able to use
the data contained within to perform either of the above tasks. If you
feel that necessary data has been omitted please contact Vince Perriello
at the above listed address so that the appropriate changes can be made.

B. Historical perspective

For those people who were not lucky enough to have an IBM PC or a system
nearly completely compatible, the world has not been very friendly. With
his implementation of the Generic Fido(tm) driver, Tom Jennings made it
possible for systems that had nothing in common with an IBM PC except an
808x-class processor, and the ability to run MS-DOS Version 2 and above,
to run his Fido(tm) software. That was a lot to ask, and a lot of people
thought it was enough.

But not everyone. While Thom Henderson was debugging Version 4.0 of his
SEAdog(tm) mail package, an "extended" Generic driver was designed (in
cooperation with Bob Hartman) as a quick kludge to help him get past a
problem with certain UART chips.The new hook was quickly pounced upon by
Vince Perriello, who, with almost DAILY prodding (ouch! it still hurts)
by Ken Kaplan,had been working with Henderson to get DEC Rainbow support
into SEAdog. Vince then coded a driver to use this hook and - Voila! -
SEAdog 4.0 started working like a champ on the Rainbow.

At the same time something was rotten in the state of Texas. Wynn Wagner
started encountering some serious difficulties in his Opus development
effort. Specifically, he couldn't force the Greenleaf(tm) Communications
Libraries to behave in exactly the way he felt Opus required. Enter Bob
Hartman.Having already enjoyed success in the effort with Thom Henderson,
he suggested to Wynn that with very few extensions, any driver that was
already SEAdog(tm) 4.0 compatible could drive Opus as well. About that
time, Vince called Wynn to discuss porting Opus to the DEC Rainbow. Wynn
called Bob, Bob called Vince, and the FOSSIL driver came into existence.

FOSSIL is an acronym for "Fido/Opus/SEAdog Standard Interface Layer". To
say that the concept has gained wide acceptance in the FidoNet community
would be an understatement. Henk Wevers' DUTCHIE package uses the FOSSIL
communications services. Ron Bemis' OUTER package uses FOSSIL services
for everything it does and as a result it is completely generic. There
are already FOSSIL implementations for the Tandy 2000, Heath/Zenith 100,
Sanyo 555 and other "non-IBM" architectures. With each new 'port' of the
spec, the potential of a properly coded FOSSIL application grows!

Fundamentals of FOSSIL implementation and use Page 2
Basic conventions and calling method

C. Basic principles of a FOSSIL driver

1) Interrupt 14H.

The one basic rule that the driver depends upon, is the ability for ANY
target machine to allow the vector for INT 14H (usually pointing to BIOS
comm functions) to be "stolen" by the driver. In a system where the INT
14H vector is used already, it must be possible to replace the "builtin"
functionality with that of a FOSSIL, when an application that wants the
use of a FOSSIL is to be run on the target machine.

2) How to install a FOSSIL driver in a system

There's no hard and fast way to do this. The FOSSIL might be implemented
as part of a device driver (like Ray Gwinn's X00.SYS) and therefore gets
loaded using a line in CONFIG.SYS at bootup time. It might be done as a
TSR (terminate and stay resident) program, in which event you install it
by running the program (DECcomm by Vince Perriello and Opus!Comm by Bob
Hartman work this way, for example).

3) How an application can detect the presence of a FOSSIL

The driver has a "signature" that can be used to determine whether it is
present in memory. At offset 6 in the INT 14H service routine is a word,
1954 hex, followed by a byte that specifies the maximum function number
supported by the driver. This is to make it possible to determine when a
driver is present and what level of functionality it provides. Also, the
Init call (see below) returns a 1954 Hex in AX. SEAdog(tm) looks at the
signature and Opus just goes for the Init. Fido doesn't do either.

4) How to call a FOSSIL function

The FOSSIL driver is entered by issuing a software Interrupt 14 Hex from
the application program. The code corresponding to the desired function
should be in 8-bit register AH. For calls that relate to communications,
the port number will be passed from the application in register DX. When
DX contains a zero (0) it signifies use of COM1, or whatever the "first"
serial port on your machine is called. A one (1) in DX points the driver
at COM2, and so on. A value of Hex FF in DX is considered a special case
where the driver should do no actual processing but return SUCCESS. In
the specific case of Init or Uninit with DX=FF,the FOSSIL should perform
all non-communications processing necessary with such calls. In some
machines (H/Z-100 for example), the FOSSIL must assume control of the
keyboard in order to service the keyboard functions.

For all functions, any registers not specifically containing a function
return can be assumed to be preserved across the call.

Fundamentals of FOSSIL implementation and use Page 3
Communications functions

D. Functions currently defined for FOSSILs

AH = 00HSet baud rate
Input:AL = baud rate code
DX = port number

This works the same as the equivalent IBM PC BIOS call, except that it
ONLY selects a baud rate. This is passed in the high order 3 bits of AL
as follows:

010 = 300 baud
011 = 600 ''
100 = 1200 ''
101 = 2400 ''
110 = 4800 ''
111 = 9600 ''
000 = 19200 '' (Replaces old 110 baud mask)
001 = 38400 '' (Replaces old 150 baud mask)

The low order 5 bits can be implemented or not by the FOSSIL, but in all
cases, if the low order bits of AL are 00011, the result should be that
the communications device should be set to eight data bits, one stop bit
and no parity. This setting is a MINIMUM REQUIREMENT of Fido, Opus and
SEAdog. For purposes of completeness, here are the IBM PC "compatible"
bit settings:

Bits 4-3 define parity: 0 0 no parity
1 0 no parity
0 1 odd parity
1 1 even parity

Bit 2 defines stop bits: 0 1 stop bit;
1 1.5 bits for 5-bit char;
2 for others

Bits 1-0 character length: 0 0 5 bits
0 1 6 bits
1 0 7 bits
1 1 8 bits

AH = 01HTransmit character
Input:AL = character
DX = port number
Output: AX contains status bits (see function 3)

AL contains the character to be sent. If there is room in the transmit
buffer the return will be immediate, otherwise it will wait until there
is room to store the character in the transmit buffer. On return, AX is
set as in a status request (see function 3).

Fundamentals of FOSSIL implementation and use Page 4
Communications functions

AH = 02HReceive character
Input:DX = port number
Output:AL = input character

If there is a character available in the receive buffer, returns with
the next character in AL. It will wait until a character is received if
none is available.

AH = 03HRequest status
Input:DX = port number
Output:AX = status bit mask (see below)

Returns with the line and modem status in AX. Status bits returned are:

In AH:
Bit 0 =RDA - input data is available in buffer
Bit 5 = THRE - room is available in output buffer
Bit 6 = TSRE - output buffer is empty

In AL:
Bit 7 =DCD - carrier detect

This can be used by the application to determine whether carrier detect
(CD) is set, signifying the presence/absence of a remote connection, as
well as monitoring both the input and output buffer status.

AH = 04HInitialize driver
Input:DX = port number
( BX = 4F50H
CX = ^C flag address --- optional )
Output:AX = 1954H if successful
BL = maximum function number supported
(not counting functions 7E and above)
BH = rev of FOSSIL doc supported

This is used to tell the driver to begin operations, and to check that
the driver is installed. This function should be called before any other
communications calls are made. At this point all interrupts involved in
supporting the comm port (specified in DX) should be set up for handling
by the FOSSIL, then enabled. If BX contains 4F50 hex, then the address
specified in BX:CX is that of a ^C flag byte in the application program,
to be incremented when ^C is detected in the keyboard service routines.
This is an optional service and only need be supported on machines where
the keyboard service can't (or won't) perform an INT 1B or INT 23 when a
Control-C is entered. DTR is raised by this call.

NOTE: Should an additional call to this service occur (2 Inits or Init,
Read,Init, etc.) the driver should reset all buffers, flow control, etc.
to the INIT state and return SUCCESS.

Fundamentals of FOSSIL implementation and use Page 5
Communications functions

AH = 05HDeinitialize driver
Input:DX = port number

This is used to tell the driver that comm port operations are ended. The
function should be called when no more comm port functions will be used
on the port specified in DX. DTR is NOT affected by this call.

AH = 06HRaise/lower DTR
Input:DX = port number
AL = DTR state to be set (1 = Raise, 0 = Lower)

This function is used to control the DTR line to the modem.AL = 0 means
lower DTR (disable the modem), and AL = 1 means to raise DTR (enable the
modem). No other function (except Init) should alter DTR.

AH = 07HReturn timer tick parameters
Output:AL = timer tick interrupt number
AH = ticks per second on interrupt number in AL
DX = approximate number of milliseconds per tick

This is used to determine the parameters of the timer tick on any given
machine. Three numbers are returned:

AL = Timer tick interrupt number
AH = Ticks per second on interrupt number shown in AL
DX = Milliseconds per tick (approximate)

Applications can use this for critical timing (granularity of less than
one second) or to set up code (such as a watchdog) that is executed on
every timer tick. See function 16H (add/delete function from timer tick)
for the preferred way of actually installing such code.

AH = 08HFlush output buffer
Input:DX = port number

This is used to force any pending output. It does not return until all
pending output has been sent. You should use this call with care. Flow
control (documented below) can make your system hang on this call in a
tight uninterruptible loop under the right circumstances.

AH = 09HPurge output buffer
Input:DX = port number

This is used to purge any pending output. Any output data remaining in
the output buffer (not transmitted yet) is discarded.

Fundamentals of FOSSIL implementation and use Page 6
Communications functions

AH = 0AHPurge input buffer
Input:DX = port number

This is used to purge any pending input. Any input data which is still
in the buffer is discarded.

AH = 0BHTransmit no wait
Input:DX = port number
Output:AX = 1 if character was accepted and 0 if not.

This is exactly the same as the "regular" transmit call, except that if
the driver is unable to buffer the character (the buffer is full), a
value of zero (0) is returned in AX. If the driver accepts the character
(room is available), a one (1) is returned in AX.

AH = 0CHNon-Destructive Read-ahead
Input:DX = port number
Output:AX = next character or FFFF if none available

Return in AX the next character in the receive buffer. If the receive
buffer is empty, return FFFF. The character returned remains in the
receive buffer. Some applications call this "peek".

AH = 0DHKeyboard read no wait
Output:AX = IBM-style keyboard scan code or FFFF if
no keyboard character available

Return in AX the next character (non-destructive read ahead) from the
keyboard; if nothing is currently in the keyboard buffer, return FFFF in
AX. Use IBM-style function key mapping in the high order byte. Scan
codes for non-"function" keys are not specifically required, but may be
included. Function keys return 0 in AL and the "scan code" in AH.

AH = 0EHKeyboard input with wait
Output:AX = IBM-style keyboard scan code

Return in AX the next character from the keyboard; wait if no character
is available. Keyboard mapping should be the same as function 13.

AH = 0FHEnable or Disable flow control on transmit
Input:AL = bit mask describing requested flow control
DX = port number

This is used to stop output when the "other end" is overwhelmed, or when
a BBS user wants to stop a screen.

Two kinds of flow control are supported:

Bit 0 = 1Enable Receiving of XON/XOFF
Bit 1 = 1CTS/RTS
Bit 2 is Reserved
Bit 3 = 1 Enable Sending of XON/XOFF

Fundamentals of FOSSIL implementation and use Page 7
Communications functions

Flow control is enabled, or disabled, by setting the appropriate bits in
AL for the types of flow control we want to ENABLE (value = 1), and/or
DISABLE (value = 0), and calling this function. Bit 2 is reserved for
DSR/DTR but is not currently supported in any implementation.

Applications using this function should set all bits ON in the high
nibble of AL as well. There is a compatible (but not identical) FOSSIL
driver implementation that uses the high nibble as a control mask. If
your application sets the high nibble to all ones, it will always work,
regardless of the method used by any given driver.

AH = 10HExtended Control-C / Control-K checking and transmit on/off
Input:AL = flags byte
DX = port number
Output:AX = status (see below)

This is used for BBS operation, primarily. A bit mask is passed in AL
with the following flags:

Bit 0enable/disable Control-C / Control-K checking
Bit 1disable/enable the transmitter

The Enable (bit 0 = 1) and Disable (Bit 0 = 0) Control-C/Control-K check
function is meant primarily for BBS use. When the checking is enabled, a
Control-C or Control-K received from the communications port will set a
flag internal to the FOSSIL driver, but will not be stored in the input
buffer. The next use of this function will return the value of this flag
in register AX then clear the flag for the next occurrence. The returned
value is used by the BBS software to determine whether output should be
halted or not.

The Disable (Bit 1 = 1) and Enable (Bit 1 = 0) Transmitter function lets
the application restrain the asynchronous driver from output in much the
same way as XON/XOFF would.

AH = 11HSet current cursor location.
Input:DH = row (line)
DL = column

This function looks exactly like like INT 10H, subfunction 2, on the IBM
PC. The cursor location is passed in DX: row in DH and column in DL. The
function treats the screen as a coordinate system whose origin (0,0) is
the upper left hand corner of the screen.

AH = 12HRead current cursor location.
Output:DH = row (line)
DL = column

Looks exactly like INT 10H, subfunction 3, on the IBM PC. The current
cursor location (using the same coordinate system as function 17) is
passed back in DX.

Fundamentals of FOSSIL implementation and use Page 8
Communications functions

AH = 13HSingle character ANSI write to screen.
Input: AL = character to display

The character in AL is sent to the screen by the fastest method possible
that allows ANSI processing to occur (if available). This routine should
not be used in such a way that DOS output (which is not re-entrant) can
not be employed by some FOSSIL driver to perform the function (in fact,
on the IBM PC that is likely to be how it's done). On some systems such
as the DEC Rainbow this will be a very fast method of screen writing.

AH = 14HEnable or disable watchdog processing
Input:AL = 1 to enable or 0 to disable watchdog
DX = port number

When watchdog is enabled, the state of the carrier detect (CD) line on
the comm port specified in DX should be constantly monitored. Should the
state of that line become FALSE (carrier lost), the system should be re-
booted, to enable the BBS (or other application) to start up again. This
monitor is not affected by Init/Uninit etc.

AH = 15HWrite character to screen using BIOS support routines
Input:AL = character to display

The character in AL is sent to the screen using BIOS-level Input/Output
routines. This differs from function 19 in that DOS I/O CANNOT be used,
as this function might be called from driver level.

AH = 16HInsert or Delete a function from the timer tick chain
Input:AL = 1 to add a function or 0 to delete one
ES:DX = address of function
Output:AX = FFFF if unsuccessful

This function is used to allow a central authority to manage the timer
interrupts, so that as code is loaded and unloaded, the integrity of the
"chain" is not compromised. Rather than using the traditional method of
saving the old contents of the timer vector, storing the address of your
routine there, and executing a far call to the "old" routine when yours
is done, instead you call this function. It manages a list of such entry
points and calls them on a timer tick (interrupt) using a FAR call. All
the usual cautions about making DOS calls apply (that is, DON'T!).

This makes it possible for a program to get in and out of the tick chain
without having to know whether another program has also done so since it
first insinuated itself. At least 4 entries should be available in the
driver's table (including one to be used by Watchdog if implemented that

Fundamentals of FOSSIL implementation and use Page 9
Communications functions

AH = 17HReboot system
Input:AL = 0 for "cold boot" or 1 for "warm boot"

Perform the old 3-finger salute. Used in extreme emergency by code that
can't seem to find a "clean" way out of the trouble it has gotten itself
into. Hopefully it won't happen while you're computing something in the
other half of a DoubleDOS system. If your machine can make a distinction
between a "cold" (power-up, self-test and boot) and a "warm" (just boot)
bootstrap, your FOSSIL should support the flag in AL. Otherwise just do
whatever bootstrap is possible.

AH = 18HRead block (transfer from FOSSIL to user buffer)
Input:CX = maximum number of characters to transfer
DX = port number
ES = segment of user buffer
DI = offset into DS of user buffer
Output:AX = number of characters actually transferred

A "no-wait" block read of 0 to 0xffff characters from the FOSSIL inbound
ring buffer to the calling routine's buffer. DS:SI are left untouched by
the call; the count of bytes actually transferred will be in AX.

AH = 19HWrite block (transfer from user buffer to FOSSIL)
Input:CX = maximum number of characters to transfer
DX = port number
ES = segment of user buffer
DI = offset into DS of user buffer
Output:AX = number of characters actually transferred

A "no-wait" block move of 0 to 0xffff characters from the calling
program's buffer into the FOSSIL outbound ring buffer. The actual number
of characters moved into the ring buffer will be returned in AX.

AH = 1AHBreak Begin or End
Input:AL = 1 to start a 'break' or 0 to end one.
DX = port number

Send a break signal to the modem. If AL=1, the driver will commence the
transmission of a 'break'. If AL=0 the driver will end the 'break'. This
is useful for communications with devices that can only go into 'command
mode' when a BREAK is received. Note: the application is responsible for
the timing of the BREAK. Also, if the FOSSIL has been restrained by an
XOFF received from the modem, the flag will be cleared. An Init or Un-
Init will stop an in-progress BREAK.

Fundamentals of FOSSIL implementation and use Page 10
Communications functions

AH = 1BHReturn information about the driver
Input:CX = size of user info buffer in bytes
DX = port number (if data about port desired)
ES = segment of user info buffer
DI = offset into DS of user info buffer
Output:AX = number of bytes actually transferred

Transfer information about the driver and its current status to the user
for use in determining, at the application level, limits of the driver.
Designed to assist "generic" applications to adjust to "foreign" gear.

The data structure currently returned by the driver is as follows (sorry
but you'll have to live with assembly syntax):

infoequ$; define begin of structure
strsizdwinfo_size; size of the structure in bytes
majverdbcurr_fossil; FOSSIL spec driver conforms to
minverdbcurr_rev; rev level of this specific driver
identddid_string; "FAR" pointer to ASCII ID string
ibufrdwibsize; size of the input buffer (bytes)
ifreedw?; number of bytes left in buffer
obufrdwobsize; size of the output buffer (bytes)
ofreedw?; number of bytes left in the buffer
swidthdbscreen_width; width of screen on this adapter
sheightdbscreen_height; height of screen " "
bauddb?; ACTUAL baud rate, computer to modem
info_size equ $-info

The ident string should be null-terminated, and NOT contain a newline.
The baud rate byte contains the bits that Function 00H would use to set
the port to that speed.

Additional information will always be passed after these, so that, for
example, offset "sheight" will never change with FOSSIL revs.

Fundamentals of FOSSIL implementation and use Page 11
"Layered Application" services

The functions below are not necessarily FOSSIL related. However, because
dispatchers that support them are hooked on Interrupt 14H, it behooves
the FOSSIL developer to support them as well to avoid fragmenting memory
with several dispatchers.

AH = 7EHInstall an "external application" function
Input:AL = code assigned to external application
DX = offset of application entry point
DS = segment of application entry point
Output:AX = 1954H
BL = code assigned to application (same as input AL)
BH = 1 if successfully installed, 0 if not.

This call is used by external application code (special screen drivers,
modem code, database code, etc) to link into the INT 14H service for use
by multiple applications. The "error return" (BH=0 with AX=1954H) should
mean that another application layer has already been installed at that
particular code. Codes 80H through BFH should be supported.

External application codes 80-83 are reserved by FOSSIL developers for
re-organizing FOSSIL services by type (comm, screen, keyboard, system).

Installed application code will be entered, via a FAR call, from the INT
14H dispatcher whenever it is entered with AH=(application code).

If the value returned in AX from this function is not 1954H, the service
code that is trying to be installed should bring up its own INT 14H code
that can service INT 14H functions 7E-BFH (80-BF are "applications").

AH = 7FHRemove an "external application" function
Input:AL = code assigned to external application
DX = offset of application entry point
DS = segment of application entry point
Output:AX = 1954H
BL = code assigned to application (same as input AL)
BH = 1 if successfully removed, 0 if not.

Removes an application's entry into the table. Usually so it can remove
itself from memory. Error return means DS:DX did not match or that there
is no entry at the slot described by AL.

An application that wants to remove itself from memory can issue the 7F
function to remove itself from the table, then, if it is successful, get
out of memory. If it had to install itself with an INT 14H dispatcher it
may back itself out, provided no other applications have been installed
on top of it (using its dispatcher).

Fundamentals of FOSSIL implementation and use Page 12

E. Validation Suite.

Well, there is one, but it's involved. Run FIDO_GEN V11w on your FOSSIL
for about a week with reasonable caller activity in the message areas,
file uploads and downloads, and FidoNet(tm) mail. Run SEAdog for a few
days, sending and receiving a reasonable number of messages. Then run
Opus for about the same amount of time. Using Ron Bemis' OUTER package
is also a useful test of the timer tick and reboot code. Some reasonable
combination of the above steps should ensure that your FOSSIL will work
with most everything coded for one.

F. Distribution.

The good folks who distribute Opus will be more than happy to take note
of your new FOSSIL driver and to add it to their distribution. And, of
course, you can upload it to any system you want, but your work will get
more publicity in the Opus community than anywhere else.

G. Technical Discussion.

A FOSSIL echomail conference exists, for the purpose of exchanging info
and implementation details for FOSSIL drivers.It is coordinated by Vince
Perriello at IFNA node 141/491. Contact him for details on how to join.
Keep in mind though, that this conference is intended SPECIFICALLY for
implementors of FOSSIL software and not as a general Q&A conference for
people who think FOSSILs have something to do with paleontology.

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