Chapter 2. API Reference
Overview ESP-IDF provides a set of consistent and flexible APIs to support both internal Ethernet MAC (EMAC)
controller and external SPI-Ethernet modules.
This programming guide is split into the following sections:
1. Basic Ethernet Concepts
2. Configure MAC and PHY
3. Connect Driver to TCP/IP Stack
4. Misc control of Ethernet driver
Basic Ethernet Concepts Ethernet is an asynchronous Carrier Sense Multiple Access with Collision Detect
(CSMA/CD) protocol/interface. It is generally not well suited for low power applications. However, with ubiq-
uitous deployment, internet connectivity, high data rates and limitless rage expandability, Ethernet can accommodate
nearly all wired communications.
Normal IEEE 802.3 compliant Ethernet frames are between 64 and 1518 bytes in length. They are made up of
five or six different fields: a destination MAC address (DA), a source MAC address (SA), a type/length field, data
payload, an optional padding field and a Cyclic Redundancy Check (CRC). Additionally, when transmitted on the
Ethernet medium, a 7-byte preamble field and Start-of-Frame (SOF) delimiter byte are appended to the beginning
of the Ethernet packet.
Thus the traffic on the twist-pair cabling will appear as shown blow:
Fig. 3: Ethernet Data Frame Format
Preamble and Start-of-Frame Delimiter The preamble contains seven bytes of 55H, it allows the receiver to lock
onto the stream of data before the actual frame arrives. The Start-of-Frame Delimiter (SFD) is a binary sequence
10101011 (as seen on the physical medium). It is sometimes considered to be part of the preamble.
When transmitting and receiving data, the preamble and SFD bytes will automatically be generated or stripped from
the packets.
Espressif Systems 170
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