Hello, This one is for the archives. I resolved the problem a few weeks ago; if any in the future finds my original posting, I would like them to find the resolution as well.
Before: My FEC code (in our debug monitor, not in Linux) set the FEC's MII_SPEED register as appropriate to give approximately a 1.24 MHz MDC. It left MII_DATA uninitialized. Thus, the MDC was always running, and my MII_read() and MII_write() functions would just write the MII_DATA register in order to do the MII transaction. This did not work, as my previous posting described. After: My FEC-init code now sets MII_SPEED to 0 and MII_DATA to 0xffffffff. My MII_read() and MII_write() routines do the following: * Write the FEC's MII_SPEED register to non-zero * Write the FEC's MII_DATA register * Read back MII_DATA, if doing a read operation * Write the FEC's MII_SPEED register to zero Thus, the MDC now runs only during a transaction, then gets turned off again. & now, I can read and write the PHY's MII registers just fine. -----Original Message----- >From: Kerl, John [mailto:John.Kerl at avnet.com] Sent: Thursday, August 22, 2002 1:13 PM To: 'linuxppc-embedded at lists.linuxppc.org' Subject: MPC857T FEC/MII failure Hello, I am experiencing a problem with the MPC857T FEC's MII interface. I want to read MII registers for our PHY (ID 24 on our board). Per the MPC857T manual: * I write 0x36 to MII_SPEED (IMMR + 0xe84). An oscilloscope probe on the PHY's MDC pin reveals a 1.235 MHz rate, within spec. * I write 0x6c060000 to MII_DATA (IMMR + 0xe80). This is: - ST=01 - OP=10 - ID=11000 - REG=00001 - TA=10 The data read back in the second 16 bits of MII_DATA are always 0xffff. This is in fact regardless of the PHY ID (I've tried all 32) or register (I've tried all 32). There are two concomitant symptoms: * If I put oscilloscope probes on the PHY's MDC and MDIO pins, then look at the MDIO pin's values at the rising edges of MDC, I see that the FEC has actually written the following: - ST=01 - OP=10 - ID=11000 - REG=00001 - TA=11 which is *not* what I asked it to do. * If I read back the MII_DATA register, *even though* I wrote 0x6c060000, I read back the value 0x6c07ffff. Note that the second 6 is now a 7. In short, I formulate a compliant request (TA=10), then the FEC mangles it (TA=11) and drives that out. It is no wonder the PHY doesn't respond. This problem is observable in our debug monitor using simple peek and poke. Thus, this is more of a PPC question than a Linux question. Has anyone seen anything similar? Thanks. ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
