!! ethtool 
ethtool コマンド

*ネットワークカードにもよるが
ethtool でケーブルテストができる

 # ethtool --cable-test eth0
 Cable test started for device eth0.
 Cable test complet
! RP4/RP5 でも。。
*https://forums.raspberrypi.com/viewtopic.php?t=365980
 diff --git a/drivers/net/phy/broadcom.c b/drivers/net/phy/broadcom.c
 index 5a24dadba..d1c9ba9a8 100644
 --- a/drivers/net/phy/broadcom.c
 +++ b/drivers/net/phy/broadcom.c
 @@ -944,10 +944,14 @@ static struct phy_driver broadcom_drivers[] = {
         .get_strings    = bcm_phy_get_strings,
         .get_stats      = bcm54xx_get_stats,
         .probe          = bcm54xx_phy_probe,
 +       .flags          = PHY_POLL_CABLE_TEST,
 +       .features       = PHY_GBIT_FEATURES,
         .config_init    = bcm54xx_config_init,
         .config_intr    = bcm_phy_config_intr,
         .suspend        = bcm54xx_suspend,
         .resume         = bcm54xx_resume,
 +       .cable_test_start = bcm_phy_cable_test_start_rdb,
 +       .cable_test_get_status = bcm_phy_cable_test_get_status_rdb,
  }, {
         .phy_id         = PHY_ID_BCM5461,
         .phy_id_mask    = 0xfffffff0,

*https://amzn.to/47tUzD2

----
!! trd 自作(ケーブル断線位置までの確認方法)
*https://jp7fkf.hatenablog.jp/entry/2017/11/10/172103
*http://designideas.cocolog-nifty.com/blog/2011/07/nano-sec-pulser.html
*http://designideas.cocolog-nifty.com/blog/2011/07/tdr-902d.html
*http://designideas.cocolog-nifty.com/blog/2011/07/nano-sec-pulser.html
*http://designideas.cocolog-nifty.com/blog/2011/07/tdr-902d.html
*http://www.mogami.com/puzzle/pzl-33.html
*https://www.google.com/search?q=tdr+%E8%A9%A6%E9%A8%93+%E5%9B%9E%E8%B7%AF%E5%9B%B3&sca_esv=ea267502e9e23089&sxsrf=AE3TifPbYtL0QqkU9igAvZ9uuANziiGX1Q%3A1754345890591&ei=ojGRaIXwI7Lj2roP0_Wz8QQ&ved=0ahUKEwiFyfzcl_KOAxWysVYBHdP6LE4Q4dUDCBI&uact=5&oq=tdr+%E8%A9%A6%E9%A8%93+%E5%9B%9E%E8%B7%AF%E5%9B%B3&gs_lp=Egxnd3Mtd2l6LXNlcnAiFHRkciDoqabpqJMg5Zue6Lev5ZuzMgoQABhHGNYEGLADMgoQABhHGNYEGLADSJQjUMMYWIkecAF4AJABAJgBAKABAKoBALgBA8gBAPgBAZgCAaACCJgDAIgGAZAGApIHATGgBwCyBwC4BwDCBwMyLTHIBwU&sclient=gws-wiz-serp
 10nSec = 100MHz
 1 nSec = 1GHz
 
 L=cvt/2
 L：電線長(m)
 c：光速（0.2998ｘ10e9 m/s)
 v：速度係数(どうやって求める？？）
 t：遅延時間（Sec)
 
 Z = (1 + r) / (1 - r) * R0
 ここに、
   Z = DUT の入力インピーダンス (0 <= Z <= ∞)
   r = TDR で得られる反射係数 (-1 <= r <= 1)
   R0 = TDR パルスジェネレータの出力インピーダンス
----
!! CAT
 5 // 100M Hz / 100ohm
 6 // 250M Hz / 100ohm
 6a// 500M Hz
 7 // 600M Hz