open https://gitlab.synchro.net/main/sbbs/-/issues/1165

SVDM: Add configurable CONNECT result speed for DOS BBS software

I tested SVDM v0.3 with SPITFIRE BBS v3.7 on Windows 10 32-bit as a possible replacement for NetSerial.

TEST ENVIRONMENT

- Windows 10 32-bit
- SPITFIRE BBS v3.7
- SVDM v0.3
- SVDM operating in Telnet/listen mode
- SPITFIRE using direct UART access, not FOSSIL
- Virtual serial configuration:
- COM2
- IRQ 3
- Base address 02F8
- TCP listen port: 2323

SVDM.INI

Mode=Telnet
Port=2323
Listen=true
Debug=true
LogLevel=Debug

[UART]
Virtualize=true
ComPort=2
IRQ=3
Address=0x2f8

LAUNCH BATCH

@ECHO OFF
CD /D C:\SVDM
SVDM.EXE C:\SF\SF.BAT

SPITFIRE MODEM CONFIGURATION

SPITFIRE successfully initializes SVDM using:

Pre-initialization: ATZ
Initialization: AT&C1&D2S95=129
Answer string: ATA

SPITFIRE reports:

Hardware data flow control enabled.
16550 UART detected.
Initializing system at 115200 bps.
OK
SPITFIRE ready for use.

This is an excellent result. SVDM successfully emulates the UART and Hayes modem interface well enough for SPITFIRE to initialize and wait for calls.

INCOMING TELNET RESULT

An incoming Telnet connection works correctly:

RING
ATA
CONNECT 9600
Connected at 9600 bps.

The caller reaches the BBS and can proceed through the login sequence.

However, SPITFIRE appears to pace its output according to the reported connection speed. The Telnet session therefore displays at approximately old 9600-bps modem speed.

The same SPITFIRE installation is fast when used with NetSerial, regardless of the BBS modem-speed configuration.

No SVDM receive-rate limit is configured:

- No Rate= entry exists in SVDM.INI.
- No -r option is used on the command line.
- SPITFIRE itself initializes successfully at 115200 bps.

SOURCE OBSERVATION

The current SVDM source appears to return CONNECT 9600 for extended modem result codes:

return response(modem, modem->ext_results ? CONNECT_9600 : CONNECT);

REQUEST

Could the reported modem connection speed be made configurable through SVDM.INI?

For example:

ConnectRate=115200

This would cause SVDM to return:

CONNECT 115200

while leaving the underlying TCP connection unrestricted.

Keeping 9600 as the default would preserve compatibility, while allowing DOS BBS packages that use the modem result speed for output pacing to operate at a higher virtual connection rate.

Suggested possible values might include:

9600
19200
38400
57600
115200

SPITFIRE has already been tested with its DTE/system baud rate set to 115200 and initializes normally.

Please let me know if the CONNECT 9600 response serves another purpose or if there is already a supported way to change it that I missed.

Thank you for creating SVDM. Its kinda awesome to see SPITFIRE v3.7 answering Telnet connections through the Synchronet Virtual DOS Modem :smile:

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https://gitlab.synchro.net/main/sbbs/-/issues/1165#note_9404

One additional observation from my production SPITFIRE setup using NetSerial:

When a caller connects through NetSerial, SPITFIRE displays:

Error correction modem detected.

That suggests NetSerial is returning a modem result or extended result code that causes SPITFIRE to recognize the connection as error-corrected, similar to a real high-speed modem.

With SVDM, SPITFIRE currently receives:

CONNECT 9600

and reports:

Connected at 9600 bps.

So there may be two related compatibility differences worth considering:

1. The reported connection speed.
2. The extended result format or flags used to indicate error correction.

My exact SPITFIRE initialization string is:

AT&C1&D2S95=129^M

NetSerial appears to work with that setup and produces both fast Telnet performance and the “Error correction modem detected” message.

I’m not sure exactly which result string or modem flag SPITFIRE is keying on, but this may be useful context when comparing SVDM’s response behavior with NetSerial.

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