Provided by: linuxcnc-uspace_2.9.4-2ubuntu2_amd64 
NAME
hm2_eth - LinuxCNC HAL driver for the Mesa Electronics Ethernet Anything IO boards, with HostMot2
firmware.
SYNOPSIS
loadrt hm2_eth [config="str[,str...]"] [board_ip=ip[,ip...]] [board_mac=mac[,mac...]]
config [default: ""]
HostMot2 config strings, described in the hostmot2(9) manpage.
board_ip [default: ""]
The IP address of the board(s), separated by commas. As shipped, the board address is
192.168.1.121.
DESCRIPTION
hm2_eth is a device driver that interfaces Mesa's ethernet based Anything I/O boards (with the HostMot2
firmware) to the LinuxCNC HAL. The supported boards are: 7I76E, 7I80DB, 7I80HD, 7I92, 7I93, 7I94, 7I95,
7I96, 7I96S, 7I97, 7I98. It also supports boards with the litehm2 firmware
(https://github.com/sensille/litehm2). The board must have its firmware loaded on the board by the
mesaflash(1) program.
hm2_eth is only available when LinuxCNC is configured with "uspace" realtime.
INTERFACE CONFIGURATION
hm2_eth should be used on a dedicated network interface, with only a cable between the PC and the board.
Wireless and USB network interfaces are not suitable.
These instructions assume your dedicated network interface is "eth1", 192.168.1/24 is an unused private
network, that the hostmot2 board is using the default address of 192.168.1.121, that you are using Debian
7 or similar, and that you do not otherwise use iptables. If any of these are false, you will need to
modify the instructions accordingly. After following all the instructions, reboot so that the changes
take effect.
It is particularly important to check that the network 192.168.1/24 is not already the private network
used by your internet router, because this is a commonly-used value. If you use another network, you
will also need to reconfigure the hostmot2 card to use an IP address on that network by using the
mesaflash(1) utility and change jumper settings. Typically, you will choose one of the networks in the
Private IPv4 address space. One common alternative is PC address 10.10.10.1, hostmot2 address
10.10.10.10.
Use of the dedicated ethernet interface while LinuxCNC is running can cause violation of realtime
guarantees. hm2_eth will automatically mitigate most accidental causes of interference.
Configure network with static address
Add these lines to the file /etc/network/interfaces to configure eth1 with a static address:
auto eth1
iface eth1 inet static
address 192.168.1.1
hardware-irq-coalesce-rx-usecs 0
PACKET LOSS
While ethernet is fairly resistant to electrical noise, many systems will not have 100% perfect packet
reception. The hm2_eth driver has a limited ability to deal with lost packets. Packet loss is detected
by transmitting an expected read or write packet count with each request, and checking the value with
each read response. When a lost packet is detected, the packet-error pin is asserted in that cycle, the
packet-error-level pin is increased, and if it reaches a threshold then a permanent low-level I/O error
is signaled.
However, not all hm2 special functions know how to properly recover from lost packets. For instance, the
encoder special function does not properly manage the index feature when packets are lost. The author
believes that this can lead to rare failures in home-to-index, which can have severe consequences.
On the other hand, pid-stepper systems will run properly for extended periods of time with packet loss on
the order of .01%, as long as following error is increased enough that having stale position feedback
does not trigger a following error. Altering the HAL configuration so that during transient packet loss
the pid and motion feedback value is equal to the command value, instead of the stale feedback value,
appears to improve tuning. This can be accomplished with a mux2(9) component for each feedback signal,
using packet-error as the mux2 sel input.
PINS
In addition to the pins documented in hostmot2(9), hm2_eth(9) creates additional pins:
(bit, out) hm2_<BoardType>.<BoardNum>.packet-error
This pin is TRUE when the most recent cycle detected a read or write error, and FALSE at other
times.
(s32, out) hm2_<BoardType>.<BoardNum>.packet-error-level
This pin shows the current error level, with higher numbers indicating a greater number of recent
detected errors. The error level is always in the range from 0 to packet-error-limit, inclusive.
(bit, out) hm2_<BoardType>.<BoardNum>.packet-error-exceeded
This pin is TRUE when the current error level is equal to the maximum, and FALSE at other times.
PARAMETERS
In addition to the parameters documented in hostmot2(9), hm2_eth(9) creates additional parameters:
(s32, rw) hm2_<BoardType>.<BoardNum>.packet-error-decrement
The amount deducted from packet-error-level in a cycle without detected read or write errors,
without going below zero.
(s32, rw) hm2_<BoardType>.<BoardNum>.packet-error-increment
The amount added to packet-error-level in a cycle without detected read or write errors, without
going above packet-error-limit.
(s32, rw) hm2_<BoardType>.<BoardNum>.packet-error-limit
The level at which a detected read or write error is treated as a permanent error. When this
error level is reached, the board's io-error pin becomes TRUE and the condition must be manually
reset.
(s32, rw) hm2_<BoardType>.<BoardNum>.packet-read-timeout
The length of time that must pass before a read request times out. If the value is less than or
equal to 0, it is interpreted as 80% of the thread period. If the value is less than 100, it is
interpreted as a percentage of the thread period. Otherwise, it is interpreted as a time in
nanoseconds. In any case, the timeout is never less than 100 microseconds.
Setting this value too low can cause spurious read errors. Setting it too high can cause realtime
delay errors.
NOTES
hm2_eth uses an iptables chain called "hm2-eth-rules-output. That technology is common to control
network access to (INPUT chain), through (FORWARD chain) or from (OUTPUT chain) your computer. Someone
who has configured a firewall on Linux has encountered iptables and is familiar with that technology.
This chain contains additional rules to control network interface while HAL is running. The chain is
created if it does not exist, and a jump to it is inserted at the beginning of the OUTPUT chain if it is
not there already. If you have an existing iptables setup, you can insert a direct jump from OUTPUT to
hm2-eth-rules-output in an order appropriate to your local network.
At (normal) exit, hm2_eth will remove the rules. After a crash, you can manually clear the rules with
sudo iptables -F hm2-eth-rules-output; the rules are also removed by a reboot.
"hardware-irq-coalesce-rx-usecs" decreases time waiting to receive a packet on most systems, but on at
least some Marvel-chipset NICs it is harmful. If the line does not improve system performance, then
remove it. A reboot is required for the value to be set back to its power-on default. This requires the
ethtool package to be installed.
BUGS
Some hostmot2 functions such uart are coded in a way that causes additional latency when used with
hm2_eth.
On the 7i92, the HAL pins for the LEDs are called CR01..CR04, but the silkscreens are CR3..CR6.
Depending on the FPGA firmware, the LEDs may initially be under control of the ethernet engine. This can
be changed until power cycle with
elbpcom 01D914000000
Depending on firmware version, this driver may cause the hardware error LED to light even though the
driver and hardware are functioning normally. This will reportedly be fixed in future bitfile updates
from Mesa.
SEE ALSO
hostmot2(9), elbpcom(1)
LICENSE
GPL
LinuxCNC Documentation 2008-05-13 HM2_ETH(9)