Keyboard shortcuts

Press ← or → to navigate between chapters

Press S or / to search in the book

Press ? to show this help

Press Esc to hide this help

Short Summary on EPICS Environment Variables

This is a short reminder which we forget frequently.

Channel Access

EPICS_CA_ADDR_LIST

  • EPICS_CA_ADDR_LIST determines where to search
  • EPICS_CA_ADDR_LIST is a list (seperated by spaces): "123.45.1.255 123.15.2.14 123.45.2.108"
  • The default of EPICS_CA_ADDR_LIST is broadcast addresses of all interfaces on the host: It works when IOC servers are on the same subnet as IOC clients.
  • Broadcast address goes to all servers on a subnet, for example, 123.45.1.255
ifconfig -a |grep broadcast
        inet 172.17.0.1  netmask 255.255.0.0  broadcast 172.17.255.255
        inet 192.168.1.180  netmask 255.255.255.0  broadcast 192.168.1.255

ip addr show |grep -E 'inet' |grep -E 'brd'
    inet 192.168.1.180/24 brd 192.168.1.255 scope global dynamic noprefixroute wlo1
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0

EPICS_CA_AUTO_ADDR_LIST

  • YES : it will include default addresses above in searches
  • NO : it does not search on default addresses
  • If you set EPICS_CA_ADDR_LIST, usually set this to NO

PV Access

[copy from https://epics-base.github.io/pvxs/netconfig.html]

A PV Access network protocol operation proceeds in two phases: PV name resolution, and data transfer. Name resolution is the process is determining which PVA server claims to provide each PV name. Once this is known, a TCP connection is open to that server, and the operation(s) are executed.

The PVA Name resolution process is similar to Channel Access protocol.

EPICS_PVA_ADDR_LIST and EPICS_PVA_NAME_SERVERS, EPICS_PVA_AUTO_ADDR_LIST

When a name needs to be resolved, a PVA client will begin sending UDP search messages to any addresses listed in EPICS_PVA_ADDR_LIST and also via TCP to any servers listed in EPICS_PVA_NAME_SERVERS which can be reached.

UDP searches are by default sent to port 5076, subject to EPICS_PVA_BROADCAST_PORT and port numbers explicitly given in EPICS_PVA_ADDR_LIST.

The addresses in EPICS_PVA_ADDR_LIST may include IPv4/6 unicast, multicast, and/or broadcast addresses. By default (cf. EPICS_PVA_AUTO_ADDR_LIST) the address list is automatically populated with the IPv4 broadcast addresses of all local network interfaces.

Searches will be repeated periodically in perpetuity until a positive response is received, or the operation is cancelled.

Reference

[1] https://controlssoftware.sns.ornl.gov/training/2019_USPAS/Presentations/06%20Channel%20Access.pdf [2] https://epics-base.github.io/pvxs/netconfig.html