The FVG318 is based on an Atheros AR5006AP-GS (aka AR2316) SoC. No idea if AtherosPort of OpenWRT supports it.

• CPU: AR2316 @ 184 MHz
• Flash: ST 25P32V6P (SPI, 4 MByte)
• RAM: Mosel-Vitelic V54C3128164VBI7 (8Mbit x 16)
• Switch: 2x Marvell 88E6060
• Ports: 8x LAN, 1x WAN
• Antenna: 1, detachable, RP-SMA
• FCC ID: PY305200007

You find internal pictures in the FCC database.

Just remove one black screw on the bottom and pull apart the two pieces of the case. Be careful with the U.FL pigtail inside.

The serial port is located on JP1:

• Pin 1: Vcc (3.3V)
• Pin 2: Rx
• Pin 3: Tx
• Pin 4: Ground

Speed is 9600.

J500 close to JP1 might be a 14 pin standard EJTAG header (not verified yet).

This unit runs VxWorks:

ar531xPlus rev 0x00000087 firmware startup...
WARNING: bootrom did not start the watchdog.
disable vlan -
tas

Atheros AR5315 default version 4.0.0.167

@$"
 1
auto-booting...

Attaching to TFFS... done.
Loading /fl/apimg1...
xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
yyyyyyyyyyyyyyyyyyyyyyyyyyy
after fd= 4 file open
2693568
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
Starting at 0x806846e0...

WARNING: bootrom did not start the watchdog.
0x000000                                                    /fl/  - Volume is OK
Reading Configuration File "/fl/apcfg".
Configuration file checksum: 4ca11 is good
in ae531xMacAddressGet, MACInfo->unit is 0
disable vlan
muxDevLoad failed for index 2
muxDevLoad failed for index 3
apInit: no wlan device
AP initilization failed!
Attached TCP/IP interface to ae unit 0
Attaching interface lo0...done
Error setting inet address of ae0 to 192.168.0.1, errno = 0x11
ERROR: AP start-up failed!  Wireless network services disabled.

iGateway Initialization Started
 setbootline
Error in IAPLstFtpLoad
Error in extnat add record 30467
WanMakeConnectionEx :: Wan Connection Type is: 2
WanMakeConnectionEx :: Wan Connection Type is: 2
WanMakeConnectionEx :: Wan Connection Type is: 2
WanMakeConnectionEx :: Wan Connection Type is: 2
Netgear modules configuration loaded


*******************************************

       FVG318 Image version 1.0.48
BSP version: NEW 2.4
create time: 09:26:00, Jul. 13th, 2007


*******************************************

You may enter a Boot Menu by pressing ESC shortly after

Atheros AR5315 default version 4.0.0.167

ar531xPlus rev 0x00000087 firmware startup...
WARNING: bootrom did not start the watchdog.
disable vlan -
tas

Atheros AR5315 default version 4.0.0.167


 1
oot]: ^?

 ?                     - print this list
 @                     - boot (load and go)
 p                     - print boot params
 c                     - change boot params
 e                     - print fatal exception
 v                     - print version
 B                     - change board data
 S                     - show board data
 n netif               - print network interface device address
 $dev(0,procnum)host:/file h=# e=# b=# g=# u=usr [pw=passwd] f=#
                           tn=targetname s=script o=other
 boot device: tffs=drive,removable     file name: /tffs0/vxWorks
 Boot flags:
   0x02  - load local system symbols
   0x04  - don't autoboot
   0x08  - quick autoboot (no countdown)
   0x20  - disable login security
   0x40  - use bootp to get boot parameters
   0x80  - use tftp to get boot image
   0x100 - use proxy arp

available boot devices:Enhanced Network Devices
 ae0 tffs

Setting boot flag to 0x20 helped me to recover a device where the firmware 2.1.12.40 (Europe version) crashed with

WARNING: bootrom did not start the watchdog.

boardData checksum failed!
/fl/  - Volume is OK
disable vlan
ae0 loaded
ae1 loaded
Attached TCP/IP interface to ae unit 0
Attaching interface lo0...done
Error setting inet address of ae0 to 192.168.1.20, errno = 0x11

Adding 13187 symbols for standalone.
Initializing platform components...

Breakpoint Exception
Caused by an Integer Divide by Zero
Exception Program Counter: 0x800197ec
Status Register: 0x10009401
Cause Register: 0x10800024
Task: 0x80fffdf0 "tRootTask"^G
-> help

I don't know if we can boot OpenWRT via tftp as described for the Netgear WGT624.