SVN eats my lunch every time I do something more difficult than status, update, or commit.
This page is here to record some hard-won successes in hopes that I can repeat them.
You could simply do a checkout of portmedia, but I gather that normally you would check out the trunk of a project.
Notice, however, that portmedia has trunk directories within each subproject directory.
Therefore, in order for portmedia to work correctly, the directories must be arranged as seen below, without the trunk directories:
The easiest way to obtain this layout is to checkout each subproject separately:
mkdir portmedia ; cd portmedia svn co https://portmedia.svn.sourceforge.net/svnroot/portmedia/portmidi/trunk portmidi svn co https://portmedia.svn.sourceforge.net/svnroot/portmedia/portsmf/trunk portsmf svn co https://portmedia.svn.sourceforge.net/svnroot/portmedia/scorealign/trunk scorealign
This eliminates the trunk directories on your machine and increases the chances of portmedia working correctly.
svn mkdir https::portmedia.svn.sourceforge.net/svnroot/portmedia/subproject svn mkdir https::portmedia.svn.sourceforge.net/svnroot/portmedia/subproject/trunk svn mkdir https::portmedia.svn.sourceforge.net/svnroot/portmedia/subproject/branches svn mkdir https::portmedia.svn.sourceforge.net/svnroot/portmedia/subproject/tags cd portmedia svn co https:://portmedia.svn.sourceforge.net/svnroot/portmedia/subproject/trunk subproject
Explanation: this makes subproject, subproject/trunk, subproject/branches, and subproject/tags in the root portmedia svn repository. Then, it checks out the trunk to the local copy.
Now you can copy files to the local subproject directory or create new files there and "svn add" them to the configuration.