Documentation of kernel API

doc/syscalls.md

@@ -450,3 +450,40 @@ This call attempts to change the current directory on a the drive specified
 in the supplied `NULL`-terminated string to the directory listed in that
 string. On success, `C` will contain `STATUS_OK`. On failure, `C` will
 containe a negative value indicating the error type.
+
+## `0x19`: Assign Device Alias
+
+Arguments:
+ - `C`: `0x19`
+ - `X`: Bank of argument structure
+ - `Y`: Address of argument structure
+
+Return Values:
+ - `C`: Status code
+
+Argument Structure:
+
+```
+    struct {
+        char *device; // The name of the device to alias
+        char *alias; // The alias to assign to it
+    };
+```
+
+Each device driver in 65X-DOS registers one or more major/minor
+number pairs to one or more "default" aliases. These aliases are
+what appear in a fully qualified pathname for a file before the
+`:` separator character.
+
+This call attempts to add a secondary name to an existing device.
+This alias will work exactly like the default name, which will still
+be valid. A device can have any number of aliases assigned to it.
+These aliases are strings which contain any character except `NULL` or
+`:`.
+
+This call will fail if the `device` argument is not an exact match to
+any device alias, or if the `alias` argument value is already in use
+as a device alias.
+
+On success, `C` will contain `STATUS_OK`. On error, `C` will contain
+a negative value which indicates the specific error type.