Emissions Testing

Wired Networking

Gigabit Ethernet - Test modes

Often users ask us how they can make the wired network transmit for emissions testing purposes.

Of the standard set of Gigabit Ethernet PHY registers the 1000BaseT Control (R9) allows configuring one of 4 test modes by setting bits 13:15:

• 0 - Normal Mode
• 1 - Test Mode 1 - Transmit Waveform Test
• 2 - Test Mode 2 - Transmit Jitter Test (MASTER mode)
• 3 - Test Mode 3 - Transmit Jitter Test (SLAVE mode)
• 4 - Test Mode 4 - Transmit Distortion Test

You should consult the datasheet for the specific PHY being used for more information on these test modes.

References:

• ​http://lxr.free-electrons.com/source/include/uapi/linux/mii.h - linux header file showing standard register names and bit values
• ​http://ftp.psu.ac.th/pub/scyld/mii-status.html
• ​http://www.ieee802.org/3/ab/public/nov97/1gig.an.presentation1.pdf

MII register access in uboot

You can read and write PHY registers from uboot via the mii command as the following example shows using a Ventana board to access eth0's PHY:

Ventana > mii info
PHY 0x00: OUI = 0x5043, Model = 0x1D, Rev = 0x01, 100baseT, FDX
Ventana > mii dump 0x00 0x05
5.     (cde1)                 -- Autonegotiation partner abilities register --
  (8000:8000) 5.15    =     1    next page able
  (4000:4000) 5.14    =     1    acknowledge
  (2000:0000) 5.13    =     0    remote fault
  (1000:0000) 5.12    =     0    (reserved)
  (0800:0800) 5.11    =     1    asymmetric pause able
  (0400:0400) 5.10    =     1    pause able
  (0200:0000) 5. 9    =     0    100BASE-T4 able
  (0100:0100) 5. 8    =     1    100BASE-X full duplex able
  (0080:0080) 5. 7    =     1    100BASE-TX able
  (0040:0040) 5. 6    =     1    10BASE-T full duplex able
  (0020:0020) 5. 5    =     1    10BASE-T able
  (001f:0001) 5. 4- 0 =     1    selector = IEEE 802.3
Ventana > mii read 0x00 0x09
0300
# set test mode 1 (set bit 13)
Ventana > mii write 0x00 0x09 0x2300
Ventana > mii read 0x00 0x09        
2300
# set test mode 2 (set bit 14)
Ventana > mii write 0x00 0x09 0x4300
Ventana > mii read 0x00 0x09        
4300
# set test mode 3 (set bit 13,14)
Ventana > mii write 0x00 0x09 0x6300
Ventana > mii read 0x00 0x09        
6300
# set test mode 4 (set bit 15)
Ventana > mii write 0x00 0x09 0x8300
Ventana > mii read 0x00 0x09        
8300

• Note the 'dump' command describes the bits but only supports R0-R5

MII register access in Linux

Many programs such as mii-tool and ethtool read and write MII regs, but don't expose a usage that lets you specify registers and/or values.

The Linux API for this is the SIOCGMIIREG/SIOCSMIIREG ioctls. Attached is a simple application using these to read and write mii regs within linux.

For example:

root@OpenWrt:/# ./mii-reg eth0 0x9
eth0 phyid=0x00 reg=0x09 val=0x0300
root@OpenWrt:/# ./mii-reg eth0 0x9 0x2300  # set test mode 2
eth0 phyid=0x00 reg=0x09 val=0x2300
root@OpenWrt:/# [   86.264882] libphy: 2188000.ethernet:00 - Link is Down
[   86.270141] br-lan: port 1(eth0) entered disabled state

root@OpenWrt:/# ./mii-reg eth0 0x9 0x300 # set normal mode
eth0 phyid=0x00 reg=0x09 val=0x0300
root@OpenWrt:/# [   91.264923] libphy: 2188000.ethernet:00 - Link is Up - 1000/Full

See mii-reg.c​ for source coe

Wireless Networking

802.11 WiFi

TX99

TX99 support enables Specific Absorption Rate (SAR) testing.

SAR is the unit of measurement for the amount of radio frequency(RF) absorbed by the body when using a wireless device. The RF exposure limits used are expressed in the terms of SAR, which is a measure of the electric and magnetic field strength and power density for transmitters operating at frequencies from 300 kHz to 100 GHz. Regulatory bodies around the world require that wireless device be evaluated to meet the RF exposure limits set forth in the governmental SAR regulations.

TX99 should only be enabled on systems undergoing certification testing and evaluation in a controlled environment.

TX99 is supported within the wireless drivers and exists for the following:

• madwifi - out of tree unsupported driver for Atheros ath5k 802.11abg radios
• ath9k - since Linux 3.14 - mainline Linux mac80211 driver for ath9k 802.11abgn radios

Examples:

• ath9k: build kernel with CONFIG_ATH9K_TX99

  # bring up a monitor mode device
  iw phy phy0 interface add moni0 type monitor
  ip link set dev moni0 up
  
  # set channel and rate
  # (see http://wireless.kernel.org/en/users/Documentation/iw#Modifying_transmit_bitrates)
  iw dev moni0 set channel 36 HT40+
  iw set bitrates mcs-5 4
  
  # set tx99 power and enable
  echo 10 > /sys/kernel/debug/ieee80211/phy0/ath9k/tx99_power
  echo 1  > /sys/kernel/debug/ieee80211/phy0/ath9k/tx99