asy" -- Device Driver" "

Device driver for asynchronous serial lines
The device driver asy supports serial ports. It uses major number 5.

asy can handle from one to 32 serial ports. The ports can be any mixture of 8250, 8250B, 16550, 16550A, and equivalent devices, including nearly all conventional COM1 through COM4 serial cards, and most non-intelligent multiport add-in cards. It automatically recognizes, and uses, on-chip FIFO, and it can specify groups of ports that share a single interrupt status.

Types of Port Configuration

Each port that asy serves has a base name, e.g., /dev/com1r. Each has its own minor device number. Different configurations of the port are selected by using different suffixes, as follows:

ll
(Local) ``Local mode'' means that the line will have a terminal plugged into it, or is connected to a modem running in command mode. Local mode uses the minor device with the modem-control bit (bit 7) set.

rr
(Remote) ``Modem control'' means that the line will have a modem plugged into it. Modem control is enabled on a serial line by resetting the modem control bit (bit 7) in the minor number for the device. This allows the system to generate a hangup signal when the modem indicates loss of carrier by dropping DCD (Data Carrier Detect). A modem line should always have its DSR, DCD and CTS pins connected. If left hanging, spurious transitions can cause severe system thrashing. An open() to a modem-control line will block until a carrier is detected (i.e., until DCD goes true).

pp
(Polled mode) ``Polled mode'' means that the port cannot generate an interrupt, but must be checked (or polled) constantly by the COHERENT system to see if activity has occurred on it. Such polling takes a significant toll on system performance. The main reason for supporting polled devices is that older style COM equipment will not allow both com1 and com3 to use interrupts at the same time, nor will it allow both com2 and com4 to use interrupts at the same time. If you use a port in polled mode, you will get better performance using one of the newer FIFO parts, such as the 16550A.

To convert from using a polled to an interrupt driven device, edit file /etc/ttys and then type the command: 
     kill quit 1

For details, see the Lexicon entry for ttys.

ff
(Flow control) A device with hardware flow control. Here, signal CTS must be active for the driver to send data out the port, and signal RTS will be set active by the driver whenever it is ready for input. Some high-speed modems, and some serial printers, are capable of using these conventions. If your equipment does not support RTS/CTS handshaking, there is no benefit to using this option.

Due to limitations in the design of the ports, you can enable interrupts on either COM1 or COM3 (or on COM2 or COM4), but not both. If you wish to use both ports simultaneously, one must be run in polled mode. For example, if you wish to open all four serial lines, you can open two of the lines in interrupt mode: you can open either COM1 or COM3 in interrupt mode, and you can open either COM2 or COM4 in interrupt mode. The other two lines must be opened in polled mode.

Opening a device in polled mode consumes many CPU cycles, based upon the speed of the highest baud rate requested. For example, on a 20 MHz 80386-based machine, polling at 9600-baud was found to consume about 15% of the CPU time. As only one device can use the interrupt line at any given time, the best approach is to make the high-speed line of the pair interrupt driven and open the low-speed or less- frequently used line in polled mode. However, if you enable a polled line for logins, the port is open and will be polled as long as the port remains open (enabled). Thus, even if a port is not in use, the fact that it has a getty on it consumes CPU cycles. As a rule of thumb, try to open a port in interrupt mode. If you cannot, use the polled version.

If you intend to use a modem on your serial port, you must insure that the DCD signal from the modem actually _f_o_l_l_o_w_s the state of carrier detect. Some modems allow the user to ``strap'' or set the DCD signal so that it is always asserted (true). This incorrect setup will cause COHERENT to think that the modem is ``connected'' to a remote modem, even when there is no such connection.

There are eight possible configurations, and eight valid suffixes. In the example of the port whose base name is com1, the configurations would be found in the directory /dev as /dev/com1l, /dev/com1r, /dev/com1pl, /dev/com1pr, /dev/com1fl, /dev/com1fr, /dev/com1fpl, and /dev/com1fpr.

Driver Configuration

asy is usually configured -- and proper names are created in directory //ddeevv -- when you install COHERENT. The following explains how to configure asy, in case you must modify the original installation.

To configure asy, do the following:

11..
Type the following command to become the superuser root: 
     su root

22..
Change to directory /etc/conf.

33..
Execute script asy/mkdev. This script walks you through the process of describing your serial ports to COHERENT.

44..
When you have successfully completed asy/mkdev, type the command: 
     bin/idmkcoh -o cohtest

This generates a new kernel, called cohtest, which incorporates the changes you described when you ran asy/mkdev.

55..
Boot your new kernel. If you do not know how to do this, read the Lexicon entry booting.

Editing /etc/default/async

The first step in reconfiguring asy is to edit /etc/default/async. This file holds the description of how the asy driver is to be configured.

asy ignores blank lines and lines that begin with a pound sign `#'; you can use them as comments if you wish. Each port that is not in a group must have a line beginning with the letter `P', followed by seven numbers:

+o
The hexadecimal base address for the port.

+o
The IRQ number, in decimal, used by the port (use zero if no interrupt line is needed).

+o
The hexadecimal value used for control lines OUT1 and OUT2 when the port is open. Permissible values are 0, 4, 8, and C. Use 4 if OUT1 must be asserted, 8 if OUT2 must be asserted, and C if both signals are needed. The most common value needed in this field is 8.

+o
One if the port needs exclusive use of its interrupt line (true for conventional COM1/COM4 equipment), zero otherwise.

+o
Default baud rate for the port.

+o
Channel number for the port (0-31).

+o
A flag to indicate if modem-status interrupts are to be disabled for this board: one if they are to be disabled, zero if they are not.

The last field is required because some chips are defective and lock up the system if modem status interrupts are enabled. This flag protects you against such problems, but at the price of disabling hardware flow control.

Many multiport boards support a separate I/O address that can be read to determine which port requires service. Each group of up to 16 ports must have a line beginning with the letter `G', followed by a separate line describing each port in the group. There are four different group types:

11..
Bits in the status port are one when the corresponding port needs service, zero otherwise. (Sealevel, Comtrol, Star Gate, Connect Tech, Boca Research.)

22..
Bits in the status port are zero when the corresponding port needs service, one otherwise. (Arnet.)

33..
The low three bits in the status port give the slot number on the card for the port needing service. (GTEK.)

44..
The low four bits in the status port give the slot number on the card for the port reading service. If no port needs service, the status port contains hexadecimal value FF. (Digiboard.)

The `G' line requires the following fields. All are in decimal, except as noted:

+o
The hexadecimal address for the group-status port.

+o
The IRQ number used by the group. Use zero if no interrupt line is needed.

+o
The hexadecimal value used for control lines OUT1 and OUT2 when the port is open (usually eight).

+o
The type number of the group -- one, two, or three, as described above.

+o
The number of ports in the group, 1 through 16.

+o
A flag to indicate if modem-status interrupts are to be disabled for this board: one if they are to be disabled, zero if they are not.

Each group line is followed by a separate `M' line for each member of the group. Fields required on the `M' line (in decimal, except as noted) are:

+o
The hexadecimal base address for the port.

+o
Default baud rate for the port.

+o
The slot number of the port within the group 0 through 7. For group types 1 and 2, slot 0 corresponds to the least-order bit in the status port, slot 7 to the highest order bit.

+o
Channel number for the port (0-31).

The following gives the async file for a system with standard COM1 through COM4 ports as channels 0 through 3, a Comtrol Hostess 550/16 as channels 4 through 19, and finally an Arnet Multiport as channels 20 through 27. 
# /etc/default/async spec for standard com1-com4
#Record formats:
#P     Port   Irq    OUT[12]       Excl   Speed   ChannelNo MS int
#G     Port   Irq    OUT[12]       Type   Number-of-SlotsNo MS int
#M     Port   Speed  Slot   Channel

# com1/2/3/4
P      3f8    4      8      1      9600   0  0
P      2f8    3      8      1      9600   1  0
P      3e8    4      8      1      9600   2  0
P      2e8    3      8      1      9600   3  0

# Hostess 550 16 - two groups of 8 ports, using irq 12
G      507    12     8      1      8      0
M      500    9600   0      4
M      508    9600   1      5
M      510    9600   2      6
M      518    9600   3      7
M      520    9600   4      8
M      528    9600   5      9
M      530    9600   6      10
M      538    9600   7      11

G      547    12     8      1      8      0
M      540    9600   0      12
M      548    9600   1      13
M      550    9600   2      14
M      558    9600   3      15
M      560    9600   4      16
M      568    9600   5      17
M      570    9600   6      18
M      578    9600   7      19

# Arnet Multiport - one group of 8 ports, using irq 7
G      272    7      0      2      8      0
M      280    9600   0      20
M      288    9600   1      21
M      290    9600   2      22
M      298    9600   3      23
M      2A0    9600   4      24
M      2A8    9600   5      25
M      2B0    9600   6      26
M      2B8    9600   7      27

You should look at the version of /etc/default/async that is shipped with COHERENT for examples of all async features, including those described above. This file includes sample configurations for every board that Mark Williams Company had available for testing.

Building a New Kernel

Now that you have described how you want asy to be configured, the next step is to build a new kernel. Log in as the superuser root and execute the following commands: 
     cd /etc/conf
     asy/mkdev
     bin/idmkcoh -o /_k_e_r_n_e_l___n_a_m_e

where kernel_name is the new kernel that includes the asy driver. To run this new kernel, simply reboot your machine.

See Also

Notes

If your system loses characters while transferring files on 4800-bps or higher-speed lines, we strongly urge you to replace your existing 8250- or 16450-based UARTs with those based upon the 16550A design, such as the National Semiconductor NS16550AFN. These newer UARTs are pin- compatible with the older UARTs. COHERENT automatically senses and enables them when it boots.