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documentation improvements to rmii.md

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Patricio Whittingslow
2026-01-25 18:50:05 -03:00
parent e83665f147
commit 470960f924
1 changed files with 9 additions and 9 deletions
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phy/rmii.md
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@@ -15,7 +15,7 @@ RMII (Reduced Media Independent Interface) reduces MII's 16 data/control pins do
| **RX_ER** | Output | Receive error indicator (optional on some PHYs) |
| **REF_CLK** | Input or Output | 50 MHz reference clock (direction depends on mode) |
All RMII signals are synchronous to the 50 MHz REF_CLK rising edge.
RMII signals that require sync are synchronous to the 50 MHz REF_CLK **rising edge.** PHY updates RXD[1:0], CRS_DV, RX_ER shortly after the rising edge. MAC should sample on the next rising edge (capturing the previous cycle's value)
## REF_CLK: Reference Clock
@@ -43,19 +43,19 @@ All RMII signals are synchronous to a continuous 50 MHz reference clock. Two mod
### Frame Transmission Sequence
First 8 bytes in transmission are preamble and start of frame delimiter (SFD).
The preamble is composed of 7 bytes, all dibits valued 0b01, so TX0=1, TX1=0.
The SFD is composed of 3 0b01 dibits and a 0b11 dibit where both TX0 and TX1 are high for a single CLKREF cycle. After the final SFD(0b11) dibit the frame data is presented of the wire.
The preamble is composed of 7 bytes, all dibits valued `0b01`, so TX0=1, TX1=0.
The SFD is composed of 3 `0b01` dibits and a `0b11` dibit where both TX0 and TX1 are high for a single CLKREF cycle. After the final SFD(`0b11`) dibit the frame data is presented of the wire.
TX_EN is asserted synchronously with the first dibit of preamble and remains HIGH throughout the entire frame (preamble, SFD, payload, CRC).
Example at 100M link mode:
```
REF_CLK: _|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_ ...
TX_EN: __|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ ... (HIGH until end of frame)
TX0: __|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾...‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾|.D ...
TX1: _______________________________...____________|‾‾‾|.A ...
TXD[1:0]: 00|01 |01 |01 |01 |01 |01 |01 |...|01 |01 |01 |11 |DA|TA|...
└───────────── Preamble (28 dibits) ─────────┘└SFD┘└─ Frame data ─...
TX_EN: __|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ ... (HIGH until end of frame)
TX0: __|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾...‾‾‾‾‾‾‾‾‾‾‾‾|.D|.T| ...
TX1: _______________________________...________|‾‾‾|.A|.A| ...
TXD[1:0]: 00|01 |01 |01 |01 |...|01 |01 |01 |01 |01 |11 |DA|TA| ...
└── Preamble (28 dibits)──┘└SFD (4 dibits)┘└─ Frame data ─...
```
@@ -235,7 +235,7 @@ The receive path uses RXD[1:0] for data and CRS_DV as a combined carrier sense a
### Frame Reception Sequence
Example supposes 100M link mode:
```
REF_CLK: _|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_ ...
REF_CLK: |‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾|_|‾| ...
CRS|CRS_DV: __|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ ... (stays HIGH until end of frame)
DV: __________|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ ...
RXD[1:0]: 00|00|00|00|01|01|01|01|01|01|01|01|01|01|11|DA|TA|...