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New section on using cheap multiport UARTS.

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Submitted by:   Helge Oldach <hmo@sep.hamburg.com>
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Nik Clayton 1999-09-26 00:09:27 +00:00
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114
en_US.ISO8859-1/books/handbook/hw/chapter.sgml
View file

@ -1,7 +1,7 @@
<!--
The FreeBSD Documentation Project
$FreeBSD$
$FreeBSD: doc/en_US.ISO_8859-1/books/handbook/hw/chapter.sgml,v 1.26 1999/09/06 06:52:57 peter Exp $
-->
<chapter id="hw">
@ -2786,6 +2786,118 @@ sio16: type 16550A (multiport master)</screen>
</step>
</procedure>
</sect4>
<sect4>
<title>Support for Cheap Multi-UART Cards</title>
<para><emphasis>Contributed by Helge Oldach
<email>hmo@sep.hamburg.com</email>, September
1999</emphasis></para>
<para>Ever wondered about FreeBSD support for your 20$ multi-I/O
card with two (or more) COM ports, sharing IRQs? Here's
how:</para>
<para>Usually the only option to support these kind of boards is to
use a distinct IRQ for each port. For example, if your CPU board
has an on-board <devicename>COM1</devicename> port (aka
<devicename>sio0</devicename>&ndash;I/O address 0x3F8 and IRQ 4)
and you have an extension board with two UARTs, you will commonly
need to configure them as <devicename>COM2</devicename> (aka
<devicename>sio1</devicename>&ndash;I/O address 0x2F8 and IRQ 3),
and the third port (aka <devicename>sio2</devicename>) as I/O
0x3E8 and IRQ 5. Obviously this is a waste of IRQ ressources, as
it should be basically possible to run both extension board ports
using a single IRQ with the <literal>COM_MULTIPORT</literal>
configuration described in the previous sections.</para>
<para>Such cheap I/O boards commonly have a 4 by 3 jumper matrix for
the COM ports, similar to the following:</para>
<programlisting> o o o *
Port A |
o * o *
Port B |
o * o o
IRQ 2 3 4 5</programlisting>
<para>Shown here is port A wired for IRQ 5 and port B wired for IRQ
3. The IRQ columns on your specific board may vary&mdash;other
boards may supply jumpers for IRQs 3, 4, 5, and 7 instead.</para>
<para>One could conclude that wiring both ports for IRQ 3 using a
handcrafted wire-made jumper covering all three connection points
in the IRQ 3 column would solve the issue, but no. You cannot
duplicate IRQ 3 because the output drivers of each UART are wired
in a &ldquo;totem pole&rdquo; fashion, so if one of the UARTs
drives IRQ 3, the output signal will not be what you would expect.
Depending on the implementation of the extension board or your
motherboard, the IRQ 3 line will continuously stay up, or always
stay low.</para>
<para>You need to decouple the IRQ drivers for the two UARTs, so
that the IRQ line of the board only goes up if (and only if) one
of the UARTs asserts a IRQ, and stays low otherwise. The solution
was proposed by Jrg Wunsch
<email>j@ida.interface-business.de</email>: To solder up a
wired-or consisting of two diodes (Germanium or Schottky-types
strongly preferred) and a 1 kOhm resistor. Here is the schematic,
starting from the 4 by 3 jumper field above:</para>
<programlisting> Diode
+---------->|-------+
/ |
o * o o | 1 kOhm
Port A +----|######|-------+
o * o o | |
Port B `-------------------+ ==+==
o * o o | Ground
\ |
+--------->|-------+
IRQ 2 3 4 5 Diode</programlisting>
<para>The cathodes of the diodes are connected to a common point,
together with a 1 kOhm pull-down resistor. It is essential to
connect the resistor to ground to avoid floating of the IRQ line
on the bus.</para>
<para>Now we are ready to configure a kernel. Staying with this
example, we would configure:</para>
<programlisting># standard on-board COM1 port
device sio0 at isa? port "IO_COM1" tty flags 0x10
# patched-up multi-I/O extension board
options COM_MULTIPORT
device sio1 at isa? port "IO_COM2" tty flags 0x205
device sio2 at isa? port "IO_COM3" tty flags 0x205 irq 3</programlisting>
<para>Note that the <literal>flags</literal> setting for
<devicename>sio1</devicename> and <devicename>sio2</devicename> is
truely essential; refer to
&man.sio.4; for details. (Generally, the <literal>2</literal> in
the "flags" attribute refers to <devicename>sio</devicename>2
which holds the IRQ, and you surely want a <literal>5</literal>
low nibble.) With kernel verbose mode turned on this should yield
something similar to this:</para>
<screen>sio0: irq maps: 0x1 0x11 0x1 0x1
sio0 at 0x3f8-0x3ff irq 4 flags 0x10 on isa
sio0: type 16550A
sio1: irq maps: 0x1 0x9 0x1 0x1
sio1 at 0x2f8-0x2ff flags 0x205 on isa
sio1: type 16550A (multiport)
sio2: irq maps: 0x1 0x9 0x1 0x1
sio2 at 0x3e8-0x3ef irq 3 flags 0x205 on isa
sio2: type 16550A (multiport master)</screen>
<para>Though <filename>/sys/i386/isa/sio.c</filename> is somewhat
cryptic with its use of the &ldquo;irq maps&rdquo; array above,
the basic idea is that you observe <literal>0x1</literal> in the
first, third, and fourth place. This means that the corresponding
IRQ was set upon output and cleared after, which is just what we
would expect. If your kernel does not display this behaviour, most
likely there is something wrong with your wiring.</para>
</sect4>
</sect3>
<sect3 id="cy">

114
en_US.ISO_8859-1/books/handbook/hw/chapter.sgml
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@ -1,7 +1,7 @@
<!--
The FreeBSD Documentation Project
$FreeBSD$
$FreeBSD: doc/en_US.ISO_8859-1/books/handbook/hw/chapter.sgml,v 1.26 1999/09/06 06:52:57 peter Exp $
-->
<chapter id="hw">
@ -2786,6 +2786,118 @@ sio16: type 16550A (multiport master)</screen>
</step>
</procedure>
</sect4>
<sect4>
<title>Support for Cheap Multi-UART Cards</title>
<para><emphasis>Contributed by Helge Oldach
<email>hmo@sep.hamburg.com</email>, September
1999</emphasis></para>
<para>Ever wondered about FreeBSD support for your 20$ multi-I/O
card with two (or more) COM ports, sharing IRQs? Here's
how:</para>
<para>Usually the only option to support these kind of boards is to
use a distinct IRQ for each port. For example, if your CPU board
has an on-board <devicename>COM1</devicename> port (aka
<devicename>sio0</devicename>&ndash;I/O address 0x3F8 and IRQ 4)
and you have an extension board with two UARTs, you will commonly
need to configure them as <devicename>COM2</devicename> (aka
<devicename>sio1</devicename>&ndash;I/O address 0x2F8 and IRQ 3),
and the third port (aka <devicename>sio2</devicename>) as I/O
0x3E8 and IRQ 5. Obviously this is a waste of IRQ ressources, as
it should be basically possible to run both extension board ports
using a single IRQ with the <literal>COM_MULTIPORT</literal>
configuration described in the previous sections.</para>
<para>Such cheap I/O boards commonly have a 4 by 3 jumper matrix for
the COM ports, similar to the following:</para>
<programlisting> o o o *
Port A |
o * o *
Port B |
o * o o
IRQ 2 3 4 5</programlisting>
<para>Shown here is port A wired for IRQ 5 and port B wired for IRQ
3. The IRQ columns on your specific board may vary&mdash;other
boards may supply jumpers for IRQs 3, 4, 5, and 7 instead.</para>
<para>One could conclude that wiring both ports for IRQ 3 using a
handcrafted wire-made jumper covering all three connection points
in the IRQ 3 column would solve the issue, but no. You cannot
duplicate IRQ 3 because the output drivers of each UART are wired
in a &ldquo;totem pole&rdquo; fashion, so if one of the UARTs
drives IRQ 3, the output signal will not be what you would expect.
Depending on the implementation of the extension board or your
motherboard, the IRQ 3 line will continuously stay up, or always
stay low.</para>
<para>You need to decouple the IRQ drivers for the two UARTs, so
that the IRQ line of the board only goes up if (and only if) one
of the UARTs asserts a IRQ, and stays low otherwise. The solution
was proposed by Jrg Wunsch
<email>j@ida.interface-business.de</email>: To solder up a
wired-or consisting of two diodes (Germanium or Schottky-types
strongly preferred) and a 1 kOhm resistor. Here is the schematic,
starting from the 4 by 3 jumper field above:</para>
<programlisting> Diode
+---------->|-------+
/ |
o * o o | 1 kOhm
Port A +----|######|-------+
o * o o | |
Port B `-------------------+ ==+==
o * o o | Ground
\ |
+--------->|-------+
IRQ 2 3 4 5 Diode</programlisting>
<para>The cathodes of the diodes are connected to a common point,
together with a 1 kOhm pull-down resistor. It is essential to
connect the resistor to ground to avoid floating of the IRQ line
on the bus.</para>
<para>Now we are ready to configure a kernel. Staying with this
example, we would configure:</para>
<programlisting># standard on-board COM1 port
device sio0 at isa? port "IO_COM1" tty flags 0x10
# patched-up multi-I/O extension board
options COM_MULTIPORT
device sio1 at isa? port "IO_COM2" tty flags 0x205
device sio2 at isa? port "IO_COM3" tty flags 0x205 irq 3</programlisting>
<para>Note that the <literal>flags</literal> setting for
<devicename>sio1</devicename> and <devicename>sio2</devicename> is
truely essential; refer to
&man.sio.4; for details. (Generally, the <literal>2</literal> in
the "flags" attribute refers to <devicename>sio</devicename>2
which holds the IRQ, and you surely want a <literal>5</literal>
low nibble.) With kernel verbose mode turned on this should yield
something similar to this:</para>
<screen>sio0: irq maps: 0x1 0x11 0x1 0x1
sio0 at 0x3f8-0x3ff irq 4 flags 0x10 on isa
sio0: type 16550A
sio1: irq maps: 0x1 0x9 0x1 0x1
sio1 at 0x2f8-0x2ff flags 0x205 on isa
sio1: type 16550A (multiport)
sio2: irq maps: 0x1 0x9 0x1 0x1
sio2 at 0x3e8-0x3ef irq 3 flags 0x205 on isa
sio2: type 16550A (multiport master)</screen>
<para>Though <filename>/sys/i386/isa/sio.c</filename> is somewhat
cryptic with its use of the &ldquo;irq maps&rdquo; array above,
the basic idea is that you observe <literal>0x1</literal> in the
first, third, and fourth place. This means that the corresponding
IRQ was set upon output and cleared after, which is just what we
would expect. If your kernel does not display this behaviour, most
likely there is something wrong with your wiring.</para>
</sect4>
</sect3>
<sect3 id="cy">