I have created a small howto for setting up Time Machine with AFP (Apple Filing Protocol) on WNR3500L router.

Optware packages needs to be installed:

netatalk
avahi
useradd
coreutils (optional to get the chown command)
openssl (optional authentication)
libgcrypt (optional authentication)

Filesystems:

1. afpd does not support NTFS fuse volume, if you only have NTFS, consider using Time Machine over a Samba Share.

2. Works on Ext3 filesystem on USB.

3. HFS - you can only mount non-journaled HFS volume under Linux, TomatoUSB has hfsplus kernel module.

Avahi setup:

Change the following settings in /opt/etc/avahi/avahi-daemon.conf

host-name=TimeMachine
allow-interfaces=br0
deny-interfaces=vlan2
enable-dbus=no

The dbus daemon did not work due to incompatible libc, so I disabled dbus support.

Create a file named /opt/etc/avahi/services/multi.service

<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
 <service-group>
    <name replace-wildcards="yes">%h</name>
    <service>
       <type>_afpovertcp._tcp</type>
       <port>548</port>
    </service>
    <service>
       <type>_device-info._tcp</type>
       <port>0</port>
       <txt-record>model=Xserve</txt-record>
    </service>
 </service-group>

Start the service with:

adduser avahi

(you need the create the user after each reboot, unless you hack /etc/passwd in NVRAM)

avahi-daemon -D

Afpd setup:

Create a directory for Time Machine backups and set up in /opt/etc/netatalk/AppleVolumes.default

/your_mount_point/TimeMachine  "Time Machine" options:tm

You may need to change the the ownership or permissions of this directory in order to be accessible for the guest or other user.

Set up /opt/etc/netatalk/afpd.conf file

Option 1. Guest authentication (nobody user)

"Time Machine" -tcp -noddp -uamlist uams_guest.so

Option 2. Guest authentication (you need to create the "guest" user with useradd)

"Time Machine" -tcp -noddp -uamlist uams_guest.so -guestname "guest"

Option 3. DHX2 authentication (create a user, place the encrypted password in /etc/passwd file)

"Time Machine" -tcp -noddp -uamlist ams_dhx2_passwd.so,uams_randnum.so

Please note that root login is not allowed.

Start "afpd" from the router prompt.

Things to do from the Mac OSX prompt:

Turn on unsupported Time Machine feature.

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

Create a backup drive

hdiutil create -size 100g -fs HFS+J -volname "Backup Drive" MacBook_xxxxxxxxxxxx.sparsebundle

where MacBook is the Mac's hostname and xxxxxxxxxxxx is the MAC address

Copy the MacBook_xxxxxxxxxxxx.sparsebundle created by hdiutil to the router under the time machine backup directory in AppleVolumes.default.

Open the Time Machine from finder and that's it.