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.
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