diff --git a/RTL8221B-app-note.md b/RTL8221B-app-note.md index 76ba59f9..061c9f4a 100644 --- a/RTL8221B-app-note.md +++ b/RTL8221B-app-note.md @@ -3,14 +3,14 @@ Warning! AI generated. The RTL8226B/RTL8221B SerDes Mode Setting Flow Application Note (Version 2.4) is essentially a "recipe book" for register writes. It moves away from the static descriptions found in the datasheet and provides state-machine logic that a driver must follow to ensure link stability. Here are the specific sequences covered in that document: -SerDes Interface Mode Switching +# SerDes Interface Mode Switching This is the most important sequence. It explains how to move the PHY between different host-side protocols. The document specifies that you cannot just change a bit; you must follow a "Teardown and Rebuild" flow: - The Flow: Power down SerDes $\rightarrow$ Change SDS_MODE_SEL (0x6A04) $\rightarrow$ Toggle PLL_RST $\rightarrow$ Wait for PATCH_READY status $\rightarrow$ Power up SerDes. - Modes Covered: SGMII (1.25G), HiSGMII (3.125G), 2500Base-X, and 10G-Lite (for 5G/10G variants). -Rate Adapter (RA) Initialization +# Rate Adapter (RA) Initialization Since 10M, 100M, and 1000M traffic is physically sent over a 2.5G SerDes lane, the PHY must "stuff" the extra bandwidth with dummy bits. @@ -31,7 +31,7 @@ Step 2: Configure RA Mode and Speed Register: MMD 31, 0x6F11, Bit 15 (RA_EN): Must be 1 to enable the adapter, Bit 5 (RA_FIX_2500): Must be 1. This forces the Rate Adapter to always output 2.5G towards the MAC, regardless of the copper link speed. Value: 0x8020 (Standard for most 2.5G designs). -Thermal Sensor Calibration and Monitoring +# Thermal Sensor Calibration and Monitoring The Application Note provides the "Enablement Flow" that is often missing from the generic datasheet: @@ -46,11 +46,12 @@ The RTL822x series can be power-hungry. The note includes a sequence for Low Pow - Voltage Adjustment: How to trim the internal LDO via 0x6601 to reduce heat if the PCB trace length allows for lower signal amplitude. - EEE (Energy Efficient Ethernet): The sequence to advertise and negotiate LPI (Low Power Idle) states. -Signal Integrity Tuning (The "Eye" Diagram) +# Signal Integrity Tuning (The "Eye" Diagram) For hardware engineers, the document provides sequences to adjust the analog physical layer: - Pre-emphasis: How to boost high-frequency signals for long backplanes. - Tx Amplitude: Adjusting the millivolt swing of the SerDes differential pairs. -Auto-Downspeed (Reliability Flow) +# Auto-Downspeed (Reliability Flow) + A unique sequence that tells the PHY to automatically drop the link speed if the cable quality is poor or if the temperature exceeds a specific threshold (OTPS - Over Temperature Protection System).