> This patch adds skew register settings for KSZ9131. It checks first > which phy is on the board and then applies the correct skew settings. > Skew settings calculation for the KSZ9131: > The i.MX6 SoC has an output skew tolerance of -100ps to 900ps. All > PCB traces where routed exactly the same length so we can calculate > the skew settings without taking the length into consideration. The > traces are all length matched. > RXC skew (PHY to MAC): > - We use the 2ns DLL controlled delay on the PHY > - We do not use the skew registers > This results in the following values: > RXC > PHY fixed Delay 2000ps > PHY Added Delay 0ps > T_setup_R min 2.00ns > T_setup_R typ 2.00ns > T_setup_R max 2.00ns > T_hold_R min 1.60ns > T_hold_R typ 2.00ns > T_hold_R max 2.40ns > That means we are well within RGMII specs. > TXC skew (MAC to PHY): > - We use the 2ns DLL controlled delay on the PHY > - We then subtract ~0.6ns with TXD[0:3] and TXC clock pad skew > register in a resulting ~1.4ns delay. > This results in the following values under consideration of the > tolerances: > TXC min TXC typ TXC max > MAC min -100ps -100ps -100ps > MAC max 900ps 900ps 900ps > PHY fixed Delay 2000ps 2000ps 2000ps > PHY added Delay -340ps -600ps -859ps > T_setup_T min 1.56ns 1.30ns 1.04ns > T_setup_T typ 2.06ns 1.80ns 1.54ns > T_setup_T max 2.56ns 2.30ns 2.04ns > T_hold_T min 1.04ns 1.30ns 1.56ns > T_hold_T typ 1.94ns 2.20ns 2.46ns > T_hold_T max 2.84ns 3.10ns 3.36ns > This shows that T_hold_T min and T_setup_T min times are out of spec > for RGMII timing. However the KSZ9131 has a minimal value for this time > of 0.8ns which is met under all circumstances. > Signed-off-by: Philippe Schenker <[email protected]> Applied to u-boot-imx, master, thanks !
Best regards, Stefano Babic -- ===================================================================== DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: +49-8142-66989-53 Fax: +49-8142-66989-80 Email: [email protected] =====================================================================
