Updated for new sio driver

2 files changed, 396 insertions, 156 deletions

diff --git a/share/man/man4/man4.i386/sio.4 b/share/man/man4/man4.i386/sio.4
index e6a0caf..d1ce9dd 100644
--- a/share/man/man4/man4.i386/sio.4
+++ b/share/man/man4/man4.i386/sio.4
@@ -36,7 +36,7 @@
 .\"	from: com.4,v 1.1 1993/08/06 11:19:07 cgd Exp
 .\"	$Id: sio.4,v 1.10 1994/05/07 01:15:10 ache Exp $
 .\"
-.Dd February 9, 1994
+.Dd June 3, 1994
 .Dt SIO 4 i386
 .Os FreeBSD
 .Sh NAME
@@ -50,14 +50,42 @@ For standard ports:
 .Cd "device sio2 at isa? port" \&"IO_COM3\&" tty irq 5 vector siointr
 .Cd "device sio3 at isa? port" \&"IO_COM4\&" tty irq 9 vector siointr
 .sp
-For multiport cards:
+For AST compatible multiport cards with 4 ports:
 .Cd "options" \&"COM_MULTIPORT\&"
-.Cd "device sio4 at isa? port 0x2a0 tty irq 12 flags 0x701 vector siointr"
-.Cd "device sio5 at isa? port 0x2a8 tty flags 0x701 vector siointr"
-.Cd "device sio6 at isa? port 0x2b0 tty flags 0x701 vector siointr"
-.Cd "device sio7 at isa? port 0x2b8 tty flags 0x701 vector siointr"
+.Cd "device sio4 at isa? port 0x2a0 tty flags 0x701"
+.Cd "device sio5 at isa? port 0x2a8 tty flags 0x701"
+.Cd "device sio6 at isa? port 0x2b0 tty flags 0x701"
+.Cd "device sio7 at isa? port 0x2b8 tty flags 0x701 irq 12 vector siointr"
 .sp
-Use 0x02 bit in flags field to disable FIFO on specified port.
+For Boca Board compatible multiport cards with 8 ports:
+.Cd "options" \&"COM_MULTIPORT\&"
+.Cd "device sio4 at isa? port 0x100 tty flags 0xb05"
+.Cd "..."
+.Cd "device sio11 at isa? port 0x138 tty flags 0xb05 irq 12 vector siointr"
+.sp
+Meaning of \fBflags\fR:
+.br
+\fB0x0001\fR shared IRQs
+.br
+\fB0x0002\fR disable FIFO
+.br
+\fB0x0004\fR no AST/4 compatible IRQ control register
+.br
+\fB0x0080\fR disable diagnostics in probe
+.br
+\fB0x\fI??\fB00\fR minor number of master port
+.sp
+Minor numbering:
+.br
+0b\fIOLIMMMMM\fR
+.br
+  call\fBO\fRut
+.br
+   \fBL\fRock
+.br
+    \fBI\fRnitial
+.br
+     \fBMMMMMM\fRinor
 .Sh DESCRIPTION
 The
 .Nm sio
@@ -67,108 +95,199 @@ driver provides support for NS8250-, NS16450-, NS16550 and NS16550A-based
 .Pf ( Tn CCITT
 .Tn V.24 )
 communications interfaces.  The NS8250 and NS16450 have single character
-buffers, the NS16550A has a 16 character FIFO buffer.
+buffers, the NS16550A has 16 character FIFO input and output buffers.
 .Pp
 Input and output for each line may set to one of following baud rates;
 50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600,
 19200, 38400, 57600, or 115200. Your hardware may limit your baud
 rate choices.
 .Pp
-The driver supports `multiport' cards. 
+The driver supports `multiport' cards.
 Multiport cards are those that have one or more groups of ports
-that share a common IRQ and Interrupt Request register set per group.
-Frequently 4 ports share 1 IRQ, some 8 port cards have 2 groups of 4 ports,
+that share an Interrupt Request (IRQ) line per group.
+Shared IRQs on different cards are not supported.
+Frequently 4 ports share 1 IRQ; some 8 port cards have 2 groups of 4 ports,
 thus using 2 IRQs.
 Some cards allow the first 2 serial ports to have seperate IRQs per port
 (as per DOS PC standard).
 .sp
+Some cards have an IRQ control register for each group.
+Some cards require special initialization related to such registers.
+Only AST/4 compatible IRQ control registers are supported.
+Some cards have an IRQ status register for each group.
+The driver does not require or use such registers yet.
+To work, the control and status registers for a group, if any,
+must be mapped to the scratch register (register 7)
+of a port in the group.
+Such a port is called a
+.Nm master
+port.
+.sp
 The
 .Nm flags
-keyword specifies for each 
+keyword may be used on each
 .Nm device sio
-line in the kernel configuration file, 
-whether the port is part of an IRQ sharing group, & if so,
-which port is the master device for
-the group (ie which port has the IRQ control registers).
-The master device is the port which
-has registers through which all interrupts of the port group are funneled.
-All ports of a port group report pending interrupts using this
-single register.
-.sp
-The master device is an integer embedded in the high byte of the
-.Nm flags
-bitfield, so all sio entries in the kernel config file that are part of a 
-multiport card must include the correct 
+line in the kernel configuration file
+to silence the probe
+or to disable the FIFO on 16550A UARTs
+(see the synopsis).
+Disabling the FIFO should rarely be necessary
+since the driver automatically adjusts the receiver
+FIFO trigger level for low latency and high efficiency.
+.sp
+The
 .Nm flags
-specification. 
-The bitwise assignment allows multiple port groups to
-be configured in one system. It does 
+keyword
+.Nm must
+be used for all ports that are part of an IRQ sharing group.
+One bit specifies IRQ sharing; another bit specifies whether the port does
 .Nm not
-imply that more than one port group (or card) can share
-the same physical interrupt line!
+require AST/4 compatible initialization.
+The minor number of the device corresponding a master port
+for the group is encoded as a bitfield in the high byte.
+The same master port must be specified for all ports in a group.
+.sp
+The
+.Nm irq
+and
+.Nm vector
+specifications must be given for master ports
+and for ports that are not part of an IRQ sharing group,
+and not for other ports.
 .Pp
-In the synopsis the 
+In the synopsis,
 .Nm flags 0x701
 means that the 8th port (sio7) is the master
-device (so the MSB of the flags), and that the ports are part of a 
-multiport card (the LSB of the flags, actually only the LS 
-.Nm bit
-).
-F.e. if you have only two standard ports in addition to multiport
-card, this
-.Nm flags
-will be
-.Nm 0x501
-(assuming the control port is 
-.Nm sio5
-).
+port, and that the port is on a multiport card with shared IRQs
+and an AST/4 compatible IRQ control register.
+.sp
+.Nm flags 0xb05
+means that the 12th port (sio11) is the master
+port, and that the port is on a multiport card with shared IRQs
+and no special IRQ control register.
 .Pp
-Which port is the master device depends on the card type. Consult
-the hardware documentation of your card.
+Which port is the master port depends on the card type.
+Consult the hardware documentation of your card.
+Since IRQ status registers are never used,
+and IRQ control registers are only used for AST/4 compatible cards,
+and some cards map the control/status registers to all ports in a group,
+any port in a group will sometimes do for the master port.
+Choose a port containing an IRQ status register for forwards compatibility,
+and the highest possible port for consistency.
 .Pp
-Serial ports controlled by the 
+Serial ports controlled by the
 .Nm sio
-driver can be used for both dialin and dialout.
-The minor number of the dialout
-port is 128 higher than that of the corresponding dialin port. Use 
-.Xr stty 1
-to enable or disable modem control as required by your setup.
+driver can be used for both `callin' and `callout'.
+For each port there is a callin device and a callout device.
+The minor number of the callout device is 128 higher
+than that of the corresponding callin port.
+The callin device is general purpose.
+Processes opening it normally wait for carrier
+and for the callout device to become inactive.
+The callout device is used to steal the port from
+processes waiting for carrier on the callin device.
+Processes opening it do not wait for carrier
+and put any processes waiting for carrier on the callin device into
+a deeper sleep so that they do not conflict with the callout session.
+The callout device is abused for handling programs that are supposed
+to work on general ports and need to open the port without waiting
+but are too stupid to do so.
 .Pp
-While testing new cards & resolving card config DIP header &
-.Nm sio flags
-settings, to avoid coms. failure from lack of full modem DC level
-settings on ports,
-you are recommended to temporarily use syntax such as:
-.Nm stty -f /dev/tty03 clocal
+The
+.Nm sio
+driver also supports an initial-state and a lock-state control
+device for each of the callin and the callout "data" devices.
+The minor number of the initial-state device is 32 higher
+than that of the corresponding data device.
+The minor number of the lock-state device is 64 higher
+than that of the corresponding data device.
+The termios settings of a data device are copied
+from those of the corresponding initial-state device
+on first opens and are not inherited from previous opens.
+Use
+.Xr stty 1
+in the normal way on the initial-state devices to program
+initial termios states suitable for your setup.
+.sp
+The lock termios state acts as flags to disable changing
+the termios state.  E.g., to lock a flag variable such as
+CRTSCTS, use
+.Nm stty crtscts
+on the lock-state device.  Speeds and special characters
+may be locked by setting the corresponding value in the lock-state
+device to any nonzero value.
+.sp
+Correct programs talking to correctly wired external devices
+work with arbitrary initial states and almost no locking,
+but other setups may benefit from changing some of the default
+initial state and locking the state.
+E.g., CRTSCTS should be locked on for devices that support
+RTS/CTS handshaking at all times and off for devices that don't
+support it at all.  CLOCAL should be locked on for devices
+that don't support carrier.  HUPCL may be locked off if you don't
+want to hang up for reason.  In general, very bad things happen
+if something is locked to the wrong state, and things should not
+be locked for devices that support more than one setting.  The
+CLOCAL flag on callin ports should be locked off for logins
+to avoid certain security holes, but this needs to be done by
+getty if the callin port is used for anything else.
 .Sh FILES
-.Bl -tag -width /dev/tty0? -compact
+.Bl -tag -width /dev/ttyi0? -compact
 .It Pa /dev/tty0?
 for hardwired terminals
+.It Pa /dev/ttyi0?
+.It Pa /dev/ttyl0?
+corresponding initial-state and lock-state devices
 .El
+.sp
 or
-.Bl -tag -width /dev/tty0? -compact
+.sp
+.Bl -tag -width /dev/ttyi0? -compact
 .It Pa /dev/ttyd?
-for dialin ports
+for callin ports
+.It Pa /dev/ttyid?
+.It Pa /dev/ttyld?
+corresponding callin initial-state and lock-state devices
+.sp
 .It Pa /dev/cua0?
-for dialout ports
+for callout ports
+.It Pa /dev/cuai0?
+.It Pa /dev/cual0?
+corresponding callout initial-state and lock-state devices
+.El
+.sp
+.Bl -tag -width /etc/rc.serial -compact
+.It Pa /etc/rc.serial
+examples of setting the initial-state and lock-state devices
 .El
 .Pp
-The devices numbers are made from the set [0-9a-z] so that more than
+The devices numbers are made from the set [0-9a-v] so that more than
 10 ports can be supported.
 /dev/tty0? and /dev/ttyd? are mutually exclusive, if you have
 /dev/tty0? corresponding /dev/ttyd? must be removed and vice versa.
 .Sh DIAGNOSTICS
 .Bl -diag
 .It sio%d: silo overflow.
-The single-character input
-.Dq silo
-has overflowed and incoming data has been lost.
-.\".It com%d: weird interrupt: %x.
-.\"The device has generated an unexpected interrupt
-.\"with the code listed.
+Problem in the interrupt handler.
+.El
+.Bl -diag
+.It sio%d: interrupt-level buffer overflow.
+Problem in the bottom half of the driver.
 .El
+.Bl -diag
+.It sio%d: tty-level buffer overflow.
+Problem in the application.
+.sp
+Input has arrived faster than the given module could process it
+and some has been lost.
+.sp
+.El
+.Bl -diag
+.It sio%d: reduced fifo trigger level to %d.
+Attempting to avoid further silo overflows.
 .Sh SEE ALSO
 .Xr tty 4 ,
+.Xr termios 4 ,
 .Xr comcontrol 8 ,
 .Xr stty 1 .
 .Sh HISTORY
@@ -180,12 +299,12 @@ driver is derived from the
 driver and is
 .Ud
 .Sh BUGS
-Data loss is not near as likely on busy systems as they are with the
+Data loss is not nearly as likely on busy systems as it is with the
 .Xr com 4
-driver but they still can occur at very high baud rates on slow systems. The
-use of NS16550A's helps lot to handle high baud rates.
+driver but it can still occur at very high baud rates on slow systems.
+The use of NS16550A's reduces system load and helps to avoid data loss.
 .Pp
-Stay away from NS16550 (so without the trailing A). These are early 
+Stay away from plain NS16550's. These are early
 implementations of the chip with non-functional FIFO hardware.
 .Pp
 The constants which define the locations
@@ -193,12 +312,13 @@ of the various serial ports are holdovers from
 .Nm DOS .
 As shown, hex addresses can be and for clarity probably should be used instead.
 .Pp
-As usual, you get what you pay for; cheap NS16550 clones generally don't work.
-.Pp
-The multiport example is based on an AST/4 card, your
-mileage may vary however. Note that on the AST/4 the card's dipswitches should 
+Note that on the AST/4 the card's dipswitches should
 .Nm not
-be set to use interrupt sharing. AST/4-like interrupt sharing is only used when 
+be set to use interrupt sharing. AST/4-like interrupt sharing is only used when
 .Nm multiple
-AST/4 cards are installed in the same system. The sio driver does not 
+AST/4 cards are installed in the same system.  The sio driver does not
 support more than 1 AST/4 on one IRQ.
+.Pp
+Hardwired terminals should not have different device names.
+.Pp
+The examples in the synopsis are too vendor-specific.
diff --git a/share/man/man4/sio.4 b/share/man/man4/sio.4
index e6a0caf..d1ce9dd 100644
--- a/share/man/man4/sio.4
+++ b/share/man/man4/sio.4
@@ -36,7 +36,7 @@
 .\"	from: com.4,v 1.1 1993/08/06 11:19:07 cgd Exp
 .\"	$Id: sio.4,v 1.10 1994/05/07 01:15:10 ache Exp $
 .\"
-.Dd February 9, 1994
+.Dd June 3, 1994
 .Dt SIO 4 i386
 .Os FreeBSD
 .Sh NAME
@@ -50,14 +50,42 @@ For standard ports:
 .Cd "device sio2 at isa? port" \&"IO_COM3\&" tty irq 5 vector siointr
 .Cd "device sio3 at isa? port" \&"IO_COM4\&" tty irq 9 vector siointr
 .sp
-For multiport cards:
+For AST compatible multiport cards with 4 ports:
 .Cd "options" \&"COM_MULTIPORT\&"
-.Cd "device sio4 at isa? port 0x2a0 tty irq 12 flags 0x701 vector siointr"
-.Cd "device sio5 at isa? port 0x2a8 tty flags 0x701 vector siointr"
-.Cd "device sio6 at isa? port 0x2b0 tty flags 0x701 vector siointr"
-.Cd "device sio7 at isa? port 0x2b8 tty flags 0x701 vector siointr"
+.Cd "device sio4 at isa? port 0x2a0 tty flags 0x701"
+.Cd "device sio5 at isa? port 0x2a8 tty flags 0x701"
+.Cd "device sio6 at isa? port 0x2b0 tty flags 0x701"
+.Cd "device sio7 at isa? port 0x2b8 tty flags 0x701 irq 12 vector siointr"
 .sp
-Use 0x02 bit in flags field to disable FIFO on specified port.
+For Boca Board compatible multiport cards with 8 ports:
+.Cd "options" \&"COM_MULTIPORT\&"
+.Cd "device sio4 at isa? port 0x100 tty flags 0xb05"
+.Cd "..."
+.Cd "device sio11 at isa? port 0x138 tty flags 0xb05 irq 12 vector siointr"
+.sp
+Meaning of \fBflags\fR:
+.br
+\fB0x0001\fR shared IRQs
+.br
+\fB0x0002\fR disable FIFO
+.br
+\fB0x0004\fR no AST/4 compatible IRQ control register
+.br
+\fB0x0080\fR disable diagnostics in probe
+.br
+\fB0x\fI??\fB00\fR minor number of master port
+.sp
+Minor numbering:
+.br
+0b\fIOLIMMMMM\fR
+.br
+  call\fBO\fRut
+.br
+   \fBL\fRock
+.br
+    \fBI\fRnitial
+.br
+     \fBMMMMMM\fRinor
 .Sh DESCRIPTION
 The
 .Nm sio
@@ -67,108 +95,199 @@ driver provides support for NS8250-, NS16450-, NS16550 and NS16550A-based
 .Pf ( Tn CCITT
 .Tn V.24 )
 communications interfaces.  The NS8250 and NS16450 have single character
-buffers, the NS16550A has a 16 character FIFO buffer.
+buffers, the NS16550A has 16 character FIFO input and output buffers.
 .Pp
 Input and output for each line may set to one of following baud rates;
 50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600,
 19200, 38400, 57600, or 115200. Your hardware may limit your baud
 rate choices.
 .Pp
-The driver supports `multiport' cards. 
+The driver supports `multiport' cards.
 Multiport cards are those that have one or more groups of ports
-that share a common IRQ and Interrupt Request register set per group.
-Frequently 4 ports share 1 IRQ, some 8 port cards have 2 groups of 4 ports,
+that share an Interrupt Request (IRQ) line per group.
+Shared IRQs on different cards are not supported.
+Frequently 4 ports share 1 IRQ; some 8 port cards have 2 groups of 4 ports,
 thus using 2 IRQs.
 Some cards allow the first 2 serial ports to have seperate IRQs per port
 (as per DOS PC standard).
 .sp
+Some cards have an IRQ control register for each group.
+Some cards require special initialization related to such registers.
+Only AST/4 compatible IRQ control registers are supported.
+Some cards have an IRQ status register for each group.
+The driver does not require or use such registers yet.
+To work, the control and status registers for a group, if any,
+must be mapped to the scratch register (register 7)
+of a port in the group.
+Such a port is called a
+.Nm master
+port.
+.sp
 The
 .Nm flags
-keyword specifies for each 
+keyword may be used on each
 .Nm device sio
-line in the kernel configuration file, 
-whether the port is part of an IRQ sharing group, & if so,
-which port is the master device for
-the group (ie which port has the IRQ control registers).
-The master device is the port which
-has registers through which all interrupts of the port group are funneled.
-All ports of a port group report pending interrupts using this
-single register.
-.sp
-The master device is an integer embedded in the high byte of the
-.Nm flags
-bitfield, so all sio entries in the kernel config file that are part of a 
-multiport card must include the correct 
+line in the kernel configuration file
+to silence the probe
+or to disable the FIFO on 16550A UARTs
+(see the synopsis).
+Disabling the FIFO should rarely be necessary
+since the driver automatically adjusts the receiver
+FIFO trigger level for low latency and high efficiency.
+.sp
+The
 .Nm flags
-specification. 
-The bitwise assignment allows multiple port groups to
-be configured in one system. It does 
+keyword
+.Nm must
+be used for all ports that are part of an IRQ sharing group.
+One bit specifies IRQ sharing; another bit specifies whether the port does
 .Nm not
-imply that more than one port group (or card) can share
-the same physical interrupt line!
+require AST/4 compatible initialization.
+The minor number of the device corresponding a master port
+for the group is encoded as a bitfield in the high byte.
+The same master port must be specified for all ports in a group.
+.sp
+The
+.Nm irq
+and
+.Nm vector
+specifications must be given for master ports
+and for ports that are not part of an IRQ sharing group,
+and not for other ports.
 .Pp
-In the synopsis the 
+In the synopsis,
 .Nm flags 0x701
 means that the 8th port (sio7) is the master
-device (so the MSB of the flags), and that the ports are part of a 
-multiport card (the LSB of the flags, actually only the LS 
-.Nm bit
-).
-F.e. if you have only two standard ports in addition to multiport
-card, this
-.Nm flags
-will be
-.Nm 0x501
-(assuming the control port is 
-.Nm sio5
-).
+port, and that the port is on a multiport card with shared IRQs
+and an AST/4 compatible IRQ control register.
+.sp
+.Nm flags 0xb05
+means that the 12th port (sio11) is the master
+port, and that the port is on a multiport card with shared IRQs
+and no special IRQ control register.
 .Pp
-Which port is the master device depends on the card type. Consult
-the hardware documentation of your card.
+Which port is the master port depends on the card type.
+Consult the hardware documentation of your card.
+Since IRQ status registers are never used,
+and IRQ control registers are only used for AST/4 compatible cards,
+and some cards map the control/status registers to all ports in a group,
+any port in a group will sometimes do for the master port.
+Choose a port containing an IRQ status register for forwards compatibility,
+and the highest possible port for consistency.
 .Pp
-Serial ports controlled by the 
+Serial ports controlled by the
 .Nm sio
-driver can be used for both dialin and dialout.
-The minor number of the dialout
-port is 128 higher than that of the corresponding dialin port. Use 
-.Xr stty 1
-to enable or disable modem control as required by your setup.
+driver can be used for both `callin' and `callout'.
+For each port there is a callin device and a callout device.
+The minor number of the callout device is 128 higher
+than that of the corresponding callin port.
+The callin device is general purpose.
+Processes opening it normally wait for carrier
+and for the callout device to become inactive.
+The callout device is used to steal the port from
+processes waiting for carrier on the callin device.
+Processes opening it do not wait for carrier
+and put any processes waiting for carrier on the callin device into
+a deeper sleep so that they do not conflict with the callout session.
+The callout device is abused for handling programs that are supposed
+to work on general ports and need to open the port without waiting
+but are too stupid to do so.
 .Pp
-While testing new cards & resolving card config DIP header &
-.Nm sio flags
-settings, to avoid coms. failure from lack of full modem DC level
-settings on ports,
-you are recommended to temporarily use syntax such as:
-.Nm stty -f /dev/tty03 clocal
+The
+.Nm sio
+driver also supports an initial-state and a lock-state control
+device for each of the callin and the callout "data" devices.
+The minor number of the initial-state device is 32 higher
+than that of the corresponding data device.
+The minor number of the lock-state device is 64 higher
+than that of the corresponding data device.
+The termios settings of a data device are copied
+from those of the corresponding initial-state device
+on first opens and are not inherited from previous opens.
+Use
+.Xr stty 1
+in the normal way on the initial-state devices to program
+initial termios states suitable for your setup.
+.sp
+The lock termios state acts as flags to disable changing
+the termios state.  E.g., to lock a flag variable such as
+CRTSCTS, use
+.Nm stty crtscts
+on the lock-state device.  Speeds and special characters
+may be locked by setting the corresponding value in the lock-state
+device to any nonzero value.
+.sp
+Correct programs talking to correctly wired external devices
+work with arbitrary initial states and almost no locking,
+but other setups may benefit from changing some of the default
+initial state and locking the state.
+E.g., CRTSCTS should be locked on for devices that support
+RTS/CTS handshaking at all times and off for devices that don't
+support it at all.  CLOCAL should be locked on for devices
+that don't support carrier.  HUPCL may be locked off if you don't
+want to hang up for reason.  In general, very bad things happen
+if something is locked to the wrong state, and things should not
+be locked for devices that support more than one setting.  The
+CLOCAL flag on callin ports should be locked off for logins
+to avoid certain security holes, but this needs to be done by
+getty if the callin port is used for anything else.
 .Sh FILES
-.Bl -tag -width /dev/tty0? -compact
+.Bl -tag -width /dev/ttyi0? -compact
 .It Pa /dev/tty0?
 for hardwired terminals
+.It Pa /dev/ttyi0?
+.It Pa /dev/ttyl0?
+corresponding initial-state and lock-state devices
 .El
+.sp
 or
-.Bl -tag -width /dev/tty0? -compact
+.sp
+.Bl -tag -width /dev/ttyi0? -compact
 .It Pa /dev/ttyd?
-for dialin ports
+for callin ports
+.It Pa /dev/ttyid?
+.It Pa /dev/ttyld?
+corresponding callin initial-state and lock-state devices
+.sp
 .It Pa /dev/cua0?
-for dialout ports
+for callout ports
+.It Pa /dev/cuai0?
+.It Pa /dev/cual0?
+corresponding callout initial-state and lock-state devices
+.El
+.sp
+.Bl -tag -width /etc/rc.serial -compact
+.It Pa /etc/rc.serial
+examples of setting the initial-state and lock-state devices
 .El
 .Pp
-The devices numbers are made from the set [0-9a-z] so that more than
+The devices numbers are made from the set [0-9a-v] so that more than
 10 ports can be supported.
 /dev/tty0? and /dev/ttyd? are mutually exclusive, if you have
 /dev/tty0? corresponding /dev/ttyd? must be removed and vice versa.
 .Sh DIAGNOSTICS
 .Bl -diag
 .It sio%d: silo overflow.
-The single-character input
-.Dq silo
-has overflowed and incoming data has been lost.
-.\".It com%d: weird interrupt: %x.
-.\"The device has generated an unexpected interrupt
-.\"with the code listed.
+Problem in the interrupt handler.
+.El
+.Bl -diag
+.It sio%d: interrupt-level buffer overflow.
+Problem in the bottom half of the driver.
 .El
+.Bl -diag
+.It sio%d: tty-level buffer overflow.
+Problem in the application.
+.sp
+Input has arrived faster than the given module could process it
+and some has been lost.
+.sp
+.El
+.Bl -diag
+.It sio%d: reduced fifo trigger level to %d.
+Attempting to avoid further silo overflows.
 .Sh SEE ALSO
 .Xr tty 4 ,
+.Xr termios 4 ,
 .Xr comcontrol 8 ,
 .Xr stty 1 .
 .Sh HISTORY
@@ -180,12 +299,12 @@ driver is derived from the
 driver and is
 .Ud
 .Sh BUGS
-Data loss is not near as likely on busy systems as they are with the
+Data loss is not nearly as likely on busy systems as it is with the
 .Xr com 4
-driver but they still can occur at very high baud rates on slow systems. The
-use of NS16550A's helps lot to handle high baud rates.
+driver but it can still occur at very high baud rates on slow systems.
+The use of NS16550A's reduces system load and helps to avoid data loss.
 .Pp
-Stay away from NS16550 (so without the trailing A). These are early 
+Stay away from plain NS16550's. These are early
 implementations of the chip with non-functional FIFO hardware.
 .Pp
 The constants which define the locations
@@ -193,12 +312,13 @@ of the various serial ports are holdovers from
 .Nm DOS .
 As shown, hex addresses can be and for clarity probably should be used instead.
 .Pp
-As usual, you get what you pay for; cheap NS16550 clones generally don't work.
-.Pp
-The multiport example is based on an AST/4 card, your
-mileage may vary however. Note that on the AST/4 the card's dipswitches should 
+Note that on the AST/4 the card's dipswitches should
 .Nm not
-be set to use interrupt sharing. AST/4-like interrupt sharing is only used when 
+be set to use interrupt sharing. AST/4-like interrupt sharing is only used when
 .Nm multiple
-AST/4 cards are installed in the same system. The sio driver does not 
+AST/4 cards are installed in the same system.  The sio driver does not
 support more than 1 AST/4 on one IRQ.
+.Pp
+Hardwired terminals should not have different device names.
+.Pp
+The examples in the synopsis are too vendor-specific.