PDK API Guide for J721E
Ethernet PHY Integration Guide


The Ethernet PHY driver is currently part of the Enet low-level driver (LLD), it's dedicated to Ethernet PHY management. It implements a state machine required to handle the lifecycle of PHYs, from initialization to link establishment.

The PHY submodule interacts with an underlying MDIO hardware through a simple MDIO driver abstraction (see EnetPhy_Mdio) in order to perform operations like detecting alive and/or linked PHYs, and for PHY register accesses. The relationship between PHY, MDIO and Enet LLD integration layer is shown below.

Enet Low-Level Driver Block Diagram

Currently, the PHY driver supports only Clause-22 devices. Clause-45 devices are not supported, but read and write helper functions are provided.

PHY Driver

The top-layer of PHY driver is located at <ENET_LLD>/src/phy/enetphy.c. This layer implements the basic APIs that are needed to communicate the driver, such as EnetPhy_open(), EnetPhy_tick(), EnetPhy_close(), etc.

The Enet LLD is capable of supporting multiple PHYs running simultaneously; each PHY has its own driver instance, its own state machine and hence will follow independent lifecycle from other PHYs.

The lifecycle of the PHYs is handled by the PHY driver via a state machine implementation. This state machine is composed of the following states:

  • FINDING: The driver will remain in this state until the PHY is detected as alive and a device-specific PHY driver has been bound to it.
  • FOUND: The driver will initiate (soft) reset if requested in PHY configuration.
  • RESET_WAIT: The driver will remain in this state while waiting for reset to complete.
  • ENABLE: The driver will put the PHY in normal mode, perform PHY device-specific extended configuration and get common capabilities supported by the MAC port and local PHY device. Depending on the requested mode (auto-negotiation or manual), the PHY will either restart auto-negotiation or manually configure speed and duplexity.
  • LOOPBACK: Last state if PHY loopback is enabled.
  • NWAY_START: The driver will remain in this state while waiting for auto-negotiation to start.
  • NWAY_WAIT: The driver will remain in this state while waiting for auto-negotiation to complete.
  • LINK_WAIT: The driver will remain in this state while waiting for link up.
  • LINKED: The PHY will remain in this state until the link is down, i.e. cable disconnection.

The diagram in the figure below provides a simplified view of the state transitions of the PHY state machine.

Simplified View of PHY State Machine

Refer to Appendix A for a more detailed view of the PHY state machine.

Device-Specific Drivers

The PHY driver model has been designed to partition device-specific operations from device-agnostic common operations. The former are implemented by PHY device specific drivers, while the latter can be carried out directly by the main PHY driver.

This model facilitates the addition of new drivers for PHY devices not yet supported in the Enet LLD. The EnetPhy_Drv structure is defined as the interface that device specific drivers must implement. Since this structure is not exposed to the application, its scope is internal to the Enet LLD.

Ethernet PHY Driver Interface

The members of the EnetPhy_Drv structure can be mandatory or optional in nature. Optional members can be set to NULL if the PHY doesn't provide an implementation for them. The list below provides a description of the purpose of each EnetPhy_Drv member.

  • name: Driver name.
  • isPhyDevSupported(): Function pointer used by the main PHY driver to check if this device specific driver support a given PHY hardware identified by its version (OUI). This function is used during PHY device to driver binding.
  • isMacModeSupported(): The main PHY driver will call this function to check if the device specific driver supports the requested MAC mode (MII, RMII, RGMII, SGMII, etc).
  • config(): The main PHY driver will call this function to allow the driver to perform any device-specific extended configuration. This function is optional and will not be called if the driver sets the function pointer to NULL.
  • reset(): Device specific reset. This function is optional and will not be called if the driver sets the function pointer to NULL.
  • isResetComplete(): The main PHY driver will call this function to check if the reset operation triggered by reset() function has completed. If reset() is provided, isResetComplete() must be provided as well.
  • readExtReg(): The main PHY driver will call this function to read extended registers.
  • writeExtReg(): The main PHY driver will call this function to write extended registers.
  • printRegs(): The main PHY driver will call this function when EnetPhy_printRegs() is called. This function is optional and will not be called if the driver sets the function pointer to NULL.

The current version of Enet LLD includes the following PHY drivers:

  • Generic PHY driver.
  • TI DP83867 RGMII PHY driver.
  • TI DP83822 RMII PHY driver.
  • VSC8514 QSGMII PHY driver.

The generic PHY driver is a special case because its implementation is limited to IEEE-Standard MII registers. Reuse of PHY generic function by other device-specific drivers is possible when their EnetPhy_Drv implementation doesn't deviate from standard. The diagram in figure below shows the reuse of extended register read/write functions by the DP83867 driver.

Ethernet PHY Driver Hierarchy

Device specific drivers can be found at <ENET_LLD>/src/phy/*.

PHY to Driver Binding

The PHY-to-driver binding is the process of selecting the best driver for a PHY device based on the device's unique identifier. This process is done by the main PHY driver upon alive detection of a PHY device and takes place in the FINDING state.

The device unique identifier is read from PHYIDR1 and PHYIDR2 registers and populated into a structure of type EnetPhy_Version.

Ethernet PHY Version

The main PHY driver has a gEnetPhyDrvs array which contains all device specific drivers that are registered and that will participate in the search for the best driver for the PHY that had been recently discovered.

static EnetPhyDrv_Handle gEnetPhyDrvs[] =
&gEnetPhyDrvVsc8514, /* VSC8514 */
&gEnetPhyDrvDp83822, /* DP83822 */
&gEnetPhyDrvDp83867, /* DP83867 */
&gEnetPhyDrvGeneric, /* Generic PHY - must be last */

In the search process, the main PHY driver will call the isPhyDevSupported() function of each registered driver. The drivers will use the EnetPhy_Version which is passed as an argument in order to determine whether the device is supported or not. If it is, isPhyDevSupported() must return true and the search process ends. If not, the search continues with the next registered device.

The generic PHY (which must be the last one in the gEnetPhyDrvs array) will be bound to the device if no other driver can support a given PHY, but the PHY full functionality can't be guaranteed.

Implementing a New PHY Driver

The following list of steps is provided as guideline when adding a new PHY driver for a device which is not supported by Enet LLD.

  • Create the public PHY specific header file at <ENET_LLD>/include/phy.
    • This header file should have the device extended configuration structure definition (if applicable) as well as auxiliary structures or enumerations.
  • Create new source file and private header file (if needed) for the new PHY driver at <ENET_LLD>/src/phy.
  • Declare a global structure of type EnetPhy_Drv, but don't make it static. This variable will be later accessed as an extern symbol by the Ethernet PHY driver.
  • Initialize EnetPhy_Drv structure with the function pointers of the device specific implementation.
    • Look for reuse of PHY generic functions if a device specific implementation is not needed.
EnetPhy_Drv gEnetPhyDrvMyDrv =
.name = "My PHY driver",
.isPhyDevSupported = MyPhy_isPhyDevSupported,
.isMacModeSupported = MyPhy_isMacModeSupported,
.config = MyPhy_config,
.reset = MyPhy_reset,
.isResetComplete = MyPhy_isResetComplete,
.runComplianceTest = NULL,
.readExtReg = GenericPhy_readExtReg,
.writeExtReg = GenericPhy_writeExtReg,
.printRegs = MyPhy_printRegs,
  • Declare the variable of type EnetPhy_Drv as extern in main PHY driver located at <ENET_LLD>/src/phy/enetphy.c. Also, add it to the gEnetPhyDrvs array.
extern EnetPhy_Drv gEnetPhyDrvGeneric;
extern EnetPhy_Drv gEnetPhyDrvDp83822;
extern EnetPhy_Drv gEnetPhyDrvDp83867;
extern EnetPhy_Drv gEnetPhyDrvVsc8514;
extern EnetPhy_Drv gEnetPhyDrvMyDrv;
static EnetPhyDrv_Handle gEnetPhyDrvs[] =
&gEnetPhyDrvMyDrv, /* My PHY driver */
&gEnetPhyDrvVsc8514, /* VSC8514 */
&gEnetPhyDrvDp83822, /* DP83822 */
&gEnetPhyDrvDp83867, /* DP83867 */
&gEnetPhyDrvGeneric, /* Generic PHY - must be last */
  • Add the PHY source file to SRCS_COMMON in the Ethernet PHY driver makefile locate at <ENET_LLD>/src/phy/makefile.
SRCS_COMMON += enetphy.c generic_phy.c
SRCS_COMMON += dp83867.c dp83822.c vsc8514.c
  • PHY driver directory is already part of the SRCDIR, so just the source name needs to be added.


Appendix A

Detailed view of the PHY state machine.

Detailed View of PHY State Machine