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 Rick Moore
at the above listed address so that the appropriate changes can be made.
Any lines changed in the current version are marked with "|" in the left
margin.

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 FSC-0015
Basic conventions and calling method Page 3

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,
1954h, 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 1954h 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 14h 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 00FFh in DX is considered a special case
where the driver should do no actual processing but return SUCCESS. In
the specific case of Init/Uninit with DX=00FFh,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, ALL REGISTERS NOT SPECIFICALLY CONTAINING A FUNCTION
RETURN VALUE MUST BE PRESERVED ACROSS THE CALL.

Fundamentals of FOSSIL implementation and use FSC-0015
Communications functions Page 4

D. Functions currently defined for FOSSILs

AH = 00h Set baud rate

Parameters:
Entry: AL = Baud rate code
DX = Port number
| Exit: AX = Port status (see function 03h) 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 = 01h Transmit character with wait

Parameters:
Entry: AL = Character
DX = Port number
Exit: AX = Port status (see function 03h)

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 03h).

AH = 02h Receive character with wait

Parameters:
Entry: DX = Port number
Exit: AH = 00h
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 = 03h Request status

Parameters:
Entry: DX = Port number
Exit: 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 1 = OVRN - the input buffer has been overrun. All
| characters received after the buffer is
| full should be discarded.
Bit 5 = THRE - room is available in output buffer
Bit 6 = TSRE - output buffer is empty

In AL:
| Bit 3 = Always 1 (always return with this bit set to 1)
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. Bit 3 of AL
is always returned set to enable programs to use it as a carrier detect
bit on hardwired (null modem) links.

AH = 04h Initialize driver

Parameters:
Entry: DX = port number
( BX = 4F50h
| ES:CX = ^C flag address --- optional )
Exit: AX = 1954h if successful
| BL = maximum function number supported
| (not counting functions 7Eh 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 4F50h, then the address
specified in ES: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 1Bh or INT 23h when
| a Control-C is entered. DTR is raised by this call. The baud rate must
| NOT be changed 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.

AH = 05h Deinitialize driver

Parameters:
Entry: DX = Port number
Exit: None

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 = 06h Raise/lower DTR

Parameters:
Entry: DX = Port number
AL = DTR state to be set (01h = Raise, 00h = Lower)
Exit: None

This function is used to control the DTR line to the modem. AL = 00h means
lower DTR (disable the modem), and AL = 01h means to raise DTR (enable the
modem). No other function (except Init) should alter DTR.

Fundamentals of FOSSIL implementation and use FSC-0015
Communications functions Page 7

AH = 07h Return timer tick parameters

Parameters:
Entry: None
Exit: 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 = 08h Flush output buffer

Parameters:
Entry: DX = Port number
Exit: None

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 = 09h Purge output buffer

Parameters:
Entry: DX = Port number
Exit: None

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

AH = 0Ah Purge input buffer

Parameters:
Entry: DX = Port number
Exit: None

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

Fundamentals of FOSSIL implementation and use FSC-0015
Communications functions Page 8

AH = 0Bh Transmit no wait

Parameters:
Entry: DX = Port number
Exit: AX = 0001h - Character was accepted
= 0000h - Character was not accepted

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 0000h is returned in AX. If the driver accepts the character
(room is available), 0001h is returned in AX.

AH = 0Ch Non-destructive read-ahead

Parameters:
Entry: DX = Port number
Exit: AH = 00h - Character is
AL = Next character available
AX = FFFFh - Character is not available

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

AH = 0Dh Keyboard read without wait

Parameters:
Entry: None
Exit: AX = IBM-style scan code (Character available)
= FFFFh (Character not available)

Return in AX the next character (non-destructive read ahead) from the
keyboard; if nothing is currently in the keyboard buffer, return FFFFh 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 00h in AL and the "scan code" in AH.

AH = 0Eh Keyboard read with wait

Parameters:
Entry: None
Exit: AX = IBM-style 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 0Dh.

AH = 0Fh Enable or disable flow control

Parameters:
Entry: AL = Bit mask describing requested flow control
DX = Port number
Exit: None

TRANSMIT flow control allows the "other end" to restrain the transmitter
when you are over-running it. RECEIVE flow control tells the FOSSIL to
attempt to do just that if it is being overwhelmed.

Two kinds of basic flow control are supported:

Bit 0 = 1 Xon/Xoff on transmit
Bit 1 = 1 CTS/RTS (CTS on transmit, RTS on receive)
Bit 2 Reserved
| Bit 3 = 1 Xon/Xoff on Receive

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.

Enabling transmit Xon/Xoff will cause the FOSSIL to stop transmitting
upon receiving an Xoff. The FOSSIL will resume transmitting when an Xon
is received.

Enabling CTS/RTS will cause the FOSSIL to cease transmitting when CTS is
lowered. Transmission will resume when CTS is raised. The FOSSIL will
drop RTS when the receive buffer reaches a predetermined percentage full
The FOSSIL will raise RTS when the receive buffer empties below the
predetermined percentage full. The point(s) at which this occurs is
left to the individual FOSSIL implementor.

| Enabling receive Xon/Xoff will cause the FOSSIL to send a Xoff when the
| receive buffer reaches a pre-determined percentage full. An Xon will be
| sent when the receive buffer empties below the pre-determined percentage
| full. The point(s) at which this occurs is left to the individual FOSSIL
| implementor.

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 = 10h Extended Control-C / Control-K checking and transmit on/off

Parameters:
Entry: AL = Bit mask (see below)
DX = Port number
Exit: AX = 0001h - Control-C/K has been received
= 0000h - Control-C/K has not been received

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

Bit 0 Enable/disable Control-C / Control-K checking
Bit 1 Disable/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 = 11h Set current cursor location.

Parameters:
Entry: DH = Row (line)
DL = Column
Exit: None

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 = 12h Read current cursor location.

Parameters:
Entry: None
Exit: 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 16h) is
passed back in DX.

AH = 13h Single character ANSI write to screen.

Parameters:
Entry: AL = Character to display
Exit: None

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 = 14h Enable or disable watchdog processing

Parameters:
Entry: AL = 01h - Enable watchdog
= 00h - Disable watchdog
DX = Port number
Exit: None

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 = 15h Write character to screen using BIOS support routines

Parameters:
Entry: AL = Character to display
Exit: None

The character in AL is sent to the screen using BIOS-level Input/Output
routines. This differs from function 13h in that DOS I/O CAN NOT be used,
as this function might be called from driver level.

AH = 16h Insert or delete a function from the timer tick chain

Parameter:
Entry: AL = 01h - Add a function
= 00h - Delete a function
| ES = Segment of function
DX = Offset of function
Exit: AX = 0000h - Operation successful
= FFFFh - Operation 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
way).

AH = 17h Reboot system

Parameters:
Entry: AL = 00h - "Cold boot"
= 01h - "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 = 18h Read block (transfer from FOSSIL to user buffer)

| Parameters:
| Entry: CX = Maximum number of characters to transfer
| DX = Port number
| ES = Segment of user buffer
| DI = Offset into ES of user buffer
| Exit: AX = Number of characters actually transferred

| A "no-wait" block read of 0 to FFFFh characters from the FOSSIL inbound
| ring buffer to the calling routine's buffer. ES:DI are left unchanged by
| the call; the count of bytes actually transferred will be returned in AX.

| AH = 19h Write block (transfer from user buffer to FOSSIL)

| Parameters:
| Entry: CX = Maximum number of characters to transfer
| DX = Port number
| ES = Segment of user buffer
| DI = Offset into ES of user buffer
| Exit: AX = Number of characters actually transferred

| A "no-wait" block move of 0 to FFFFh characters from the calling
| program's buffer into the FOSSIL outbound ring buffer. ES:DI are left
| unchanged by the call; the count of bytes actually transferred will be
| returned in AX.

| AH = 1Ah Break begin or end

| Parameters:
| Entry: AL = 01h - Start sending 'break' = 00h - Stop sending 'break'
| DX = port number
| Exit: None

| Send a break signal to the modem. If AL=01h the driver will commence the
| transmission of a break. If AL=00h 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 FSC-0015
Communications functions Page 14

| AH = 1Bh Return information about the driver

| Parameters:
| Entry: CX = Size of user info buffer in bytes
| DX = Port number
| ES = Segment of user info buffer
| DI = Offset into ES of user info buffer
| Exit: 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):

| info equ $ ; define begin of structure
| strsiz dw info_size ; size of the structure in bytes
| majver db curr_fossil ; FOSSIL spec driver conforms to
| minver db curr_rev ; rev level of this specific driver
| ident dd id_string ; "FAR" pointer to ASCII ID string
| ibufr dw ibsize ; size of the input buffer (bytes)
| ifree dw ? ; number of bytes left in buffer
| obufr dw obsize ; size of the output buffer (bytes)
| ofree dw ? ; number of bytes left in the buffer
| swidth db screen_width ; width of screen on this adapter
| sheight db screen_height ; height of screen " "
| baud db ? ; 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.

| The fields related to a particular port (buffer size, space left in the
| buffer, baud rate) will be undefined if port FFh or an invalid port is
| contained in DX.

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

| 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 = 7Eh Install an "external application" function

| Parameters:
| Entry: AL = Code assigned to external application
| DX = Offset of application entry point
| ES = Segment of application entry point
| Exit: AX = 1954h
| BL = Code assigned to application (same as input AL)
| BH = 01h - Installation was successful
| = 00h - Installation failed

| 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 80h-83h 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 7h-BFh (80h-BFh are "applications").

| AH = 7Fh Remove an "external application" function

| Parameters:
| Entry: AL = Code assigned to external application
| DX = Offset of application entry point
| ES = Segment of application entry point
| Exit: AX = 1954h
| BL = Code assigned to application (same as input AL)
| BH = 01h - Removal was successful
| = 00h - Removal failed

| Removes an application's entry into the table. Usually so it can remove
| itself from memory. Error return means ES: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).

Well, there is one, but it's involved. Here is a list of software that
is known to use FOSSIL calls, and the range of calls used by that
software:

Software package Fossil calls used

Fido, V11w, generic version 00h - 07h
SEAdog, V4.1b 00h - 0Eh
Opus, V1.03a 00h - 17h
BinkleyTerm, V1.30 00h - 1Bh

While there is certainly no guarantee that your FOSSIL is bug-free if
all the above software runs with it, you have probably done as much
as you can in a test environment if your FOSSIL is tested with each of
these packages.

A FOSSIL echomail conference exists, for the purpose of exchanging info
and implementation details for FOSSIL drivers. It is coordinated by Ray
Gwinn at FidoNet node 1:109/639. 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.

This document may be distribute freely as long as it is not modified in
any way. Please list all changes and deviations in a given FOSSIL
implementation in an addendum contained in a separate file added to the
FOSSIL archive. Also, please do not distribute this document without
the accompanying version of FOSSIL.CHT. This will help avoid confusion,
among both FOSSIL implementors and application developers.