Technical Q&A NW49

OT Driver returns EINVAL error for TCP/IP program, but AppleTalk works fine

Q: I've developed a DLPI driver to support my network hardware product under Open Transport. In testing the driver, I have no problem with supporting AppleTalk, but when I try to access TCP services, error -3221 is always returned no matter what TCP/IP application is used. What's happening?

A: The most common reason for this error is that in setting up the TCP/IP stack, the TCP/IP configurator makes a check which is not made while setting up the AppleTalk stack. The configurator verifies that the fModuleName registered in the OTPortRecord for the port, matches the module name that is set in the module_info global from the DLPI driver. If the two names do not match exactly, the configuration fails and error -3221 is returned to the OpenEndpoint call.

This problem is most easily corrected by examining the module_info global, and verifying that the fModuleName field matches the module name entered for the corresponding port record. To access the port record, here is a sample application you can download (along with source code) which displays all of the registered port records for a system, along with the associated port name and module name.

When Open Transport makes the OTRegisterPort call to a PCI card, the module name used is the "name" Name Register property for the card. If, however, you have developed a custom port scanner for your card, then the module name will be whatever is passed in the fModuleName field of the Port Record structure passed to the OTRegisterPort call.

Under PC Card Manager 3.0, the network driver expert first looks into the Name Registry to check whether a custom enabler for the network card has registered a "port-module" property (C-String). If so, then this property will be used in the fModuleName field of the OTPortRecord card that is passed to the OTRegisterPort call to have OT recognize the new device. If there is no "port-module" Name Registry property created for the card by a custom enabler, then the PC Card Manager expert will build the name to register with OTRegisterPort, from the "name" property (with some minor modifications).

For example, suppose the "name" property initially looks something like:

ethernet,pc1,MY ETHERNET CARD

The PC Card Manager 3.0 expert will truncate this name to:

pc1,MY ETHERNET CARD

This happens because the module name must be a string no longer than 31 characters. The ethernet, portion of the string will be truncated in order to reduce the length of the module name. If you are unaware that this is happening, you may enter the wrong name into the module_info record, instead of the right name, pc1,MY ETHERNET CARD.

The result is that the registered fModuleName will not match that of the name in the module_info record, the TCP/IP configuration module name check fails, and the EINVAL error is returned.