Chapter 14 Configuring IPC

This chapter describes how to configure the IPC feature within the ChorusOS operating system to provide either local IPC communication or remote IPC communication over Ethernet.

• "IPC Feature Configuration" introduces the three different IPC configurations, and how to add them to the ChorusOS operating system.

• "Specific IPC Configuration" describes remote IPC configuration in more detail.

Generic IPC Configuration

IPC Feature Configuration

The ChorusOS IPC feature is an optional component of the ChorusOS microkernel that can be added in two different configurations:

1. Local IPC. This configuration provides only local IPC communications.

2. Local IPC + remote IPC. This configuration enables local and remote IPC communications to take place over a network data-link such as Ethernet or ATM (Asynchronous Transfer Method). This data-link is also called an external data-link, which means that the data-link driver is implemented within an independent driver outside of the microkernel.

The comand-line configuration tool configurator(1CC) is used to set up each configuration.

To configure the local IPC feature:

% configurator -set IPC=true 

To configure the local IPC + remote IPC feature:

% configurator -set IPC_REMOTE=true

Site Number Administration

The IPC feature has the concept of a site number, a 32-bit unsigned integer that uniquely identifies a target board. Applications exchange messages through IPC ports, which are designated by a global identifier that includes the site number of the target board where the port is located.

The site number of a target is sent to the microkernel at boot time in one of two ways:

1. dynamically, by the boot program, which sets the siteNumber field of the bootConf structure before invoking the microkernel start entry.

2. statically, by setting the chorusSiteId microkernel tunable in the ChorusOS system image built on the host:

   % configurator -set chorusSiteId=n

   n is the site number assigned to the target board. This number can be specified in hexadecimal, by prefixing the number with 0x, or decimal.

When the site number is set dynamically, it is the responsibility of the boot program to determine the site number of the target. The method by which the site number is found by the boot program is fully boot dependent, and specific to the target board. It may, for example, be stored in NVRAM, dynamically generated from a unique board identifier. When the target is booted with the standard ChorusOS network boot monitor, the whole IP address used by the boot monitor is provided as the site number of the target.

When the site number is set statically, the site number is fixed within the system image. This approach is less flexible than the dynamic method because the same system image cannot be booted on similar target boards. A system image with a unique site number must be built for each target. For this reason, it should only be used when there is no way for the boot program to determine the site number of the target board.

The value of the site number set with the chorusSiteId tunable takes precedence over the value of the site number provided by the boot program.

The site number is set to zero by default. If the IPC_REMOTE feature has been enabled, and the site number remains at zero, the following message is displayed on the system console:

WARNING - LOCAL SITE ID. NOT SET => REMOTE IPC disabled

Only local IPC communications are enabled if the site number has not been set.

Specific IPC Configuration

Remote IPC over Ethernet Data-link

To configure the remote IPC over Ethernet feature, set the IPC_REMOTE feature to true. In addition, switch on the IOM_IPC feature:

% configurator -set IOM_IPC=true

This adds the Ethernet-specific module into the C_OS component which acts as the IPC Ethernet data-link driver.

Once you have built and booted the ChorusOS system image on the target board tgtbd1, the IPC Ethernet data-link can be dynamically started. Use the built-in ethIpcStackAttach command of C_INIT (running on the target board tgtbd1) :

% rsh tgtbd1 ethIpcStackAttach ethernet-device-name

The ethernet-device-name argument is the name of the Ethernet device with which your remote IPC stack will communicate. This name is the full pathname of the Ethernet device in the target device tree, displayed on the target system console by the system at boot time. For example, a genesis2 board with a dec21140 Ethernet controller connected through a raven PCI bridge, has the pathname /raven/pci1011,9@e,0. This argument is only needed when the target board has more than one Ethernet controller.

See the ethIpcStackAttach(1M) man page for more details.

The following example describes how to build a ChorusOS system image for two similar PowerPC-based target boards, tgtbd1 and tgtbd2, each with an Ethernet controller. Site numbers must be unique and statically configured in each ChorusOS system image.

1. Configure Remote IPC over Ethernet, if not already configured:

   % configurator -set IPC=true % configurator -set IPC_REMOTE=true% configurator -set IOM_IPC=true

2. Assign a site number to tgtbd1, then build and uniquely identify the ChorusOS system image:

   % configurator -set chorusSiteId=1 % make chorus % mv chorus.RAM chorus.RAM.tgtbd1

   Assign a site number to tgtbd2, then build and uniquely identify the ChorusOS system image:

   % configurator -set chorusSiteId=2 % make chorus % mv chorus.RAM chorus.RAM.tgtbd2

3. Once you have booted the chorus.RAM.tgtbd1 system image on tgtbd1 and the chorus.RAM.tgtbd2 system image on tgtbd2, run the ethIpcStackAttach command:

   % rsh tgtbd1 ethIpcStackAttach % rsh tgtbd2 ethIpcStackAttach

Applications that need to communicate through remote IPC can now be launched on the tgtbd1 and tgtbd2 targets.