MCBXC167: HOW TO ACCESS AX88796 EMBEDDED PHY REGISTER

Information in this article applies to:

• MCB-XC167 Evaluation Boards

QUESTION

I need to access the embedded PHY registers (MR0 - MR31) of the AX88796 ethernet controller to retrieve the link status and to set the autonegotiation advertisement mode. These registers are not memory-mapped. How can I access them?

ANSWER

These station management registers are part of the MII interface which needs to be accessed over an internal serial interface. The protocol on this interface is described in chapter 6.5 of the AX88796 manual. The code below can be used to read from or write into these registers.

#include "AX88796.h"
#include <absacc.h>

static void shiftout (unsigned int value, unsigned int count) {
  unsigned int  mask,i;
  unsigned char mdoval;

  mask = 1 << (count - 1);
  for(i = 0; i < count; i++) {   // send 'count' bits to PHY register
    if (mask & value) {
      mdoval = MEMR_MDO;         // MDO=1
    } else {
      mdoval = 0x00;             // MDO=0
    }
    HVAR(unsigned char, M2EEP) = mdoval;
    HVAR(unsigned char, M2EEP) = mdoval | MEMR_MDC;  // positive transition of clock
    mask >>= 1;
  }
}

//WRITE TO AX88796 MII REGISTERS
void Write_MII(unsigned char regad,unsigned int mii_data) {
  shiftout (0xF5, 8);     // send 4 bits preamble (1111B),
                          // 2 bits start frame (ST = 01B)
                          // 2 bits operation code (OP = 01B for 'write')
  shiftout (0x10, 5);     //Send 5 bits PHY address = 10000B for internal PHY
  shiftout (regad, 5);    //Send 5 bits PHY register address
  shiftout (0x02, 2);     //Send 2 bits turnaround time (10B)
  shiftout (mii_data, 16);//Send 16 bits data
}

//READ MII AX88796 REGISTERS
unsigned int Read_MII(unsigned char regad) {
  unsigned char i, mdival;
  unsigned int  result;

  shiftout (0xF6, 8);     // send 4 bits preamble (1111B),
                          // 2 bits start frame (ST = 01B)
                          // 2 bits operation code (OP = 10B for 'read')
  shiftout (0x10, 5);     //Send 5 bits PHY address = 10000B for internal PHY
  shiftout (regad, 5);    //Send 5 bits PHY register address
  shiftout (0x00, 2);     //Send 2 bits turnaround time (00B)
  result = 0x0000;
  for(i = 0; i < 16; ++i){//Read 16 bits of data from PHY
    result <<= 1;
    HVAR(unsigned char, M2EEP) = MEMR_MDC;  // positive transition of clock
    mdival = HVAR(unsigned char, M2EEP);
    if (mdival & 0x04) {
      result |= 0x01;
    }
    HVAR(unsigned char, M2EEP) = 0x00;      // MDO=0
  }
  return (result);
}

This code fragment can be used with the EasyWeb example (C:\Keil\C166\Boards\Keil MCB-XC167\EasyWEB) as well as all ethernet examples of ARTX-166 (e.g. C:\Keil\C166\AR166\Examples\Http_demo)

MORE INFORMATION

• AX88796 manual on Keil CD:\Boards\MCBXC167\AX88796.pdf

Last Reviewed: Thursday, February 09, 2006