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I have observed what seem to be strange
initialization problems with the ethernet
driver:
I usually configure RTEMS networking by
BOOTP (the problem has nothing to do with
BOOTP but I just want to describe my
environment). Sometimes (it can actually
happen quite frequently, like 1 out of 4
attempts but since yesterday when I decided
to hunt this down more systematically
the problem seems to have gone - typical!)
networking fails to initialize properly:
BOOTP requests are sent (to the MAC),
TX interrupts occur and the TX MIB
counters increment - i.e., everything
seems normal but no data can be seen on
the wire. Also, even though we are on
a quite busy network, the receiver
doesn't see anything, i.e., 0 RX
interrupts, RX MIB counters for broadcast
packets remain steady at zero etc.
In brief, everyting seems normal at the
MAC and higher layers but no connection
to the wire seems to be established.
Some further tests reveal (system under
test is in the 'bad' state):
1 communication with the BCM5461 PHY
is normal. Registers can be read/written
and everything seems normal. In particular,
the link status is reported OK: disconnect
the cable and MII - BMSR bit 1<<2 is clear,
reconnect the cable and BMSR[2] is set.
Restart autoneg, the link goes and comes
back after a short while.
2 setting the loopback bit in the TSEC's
MACCFG1 register correctly feeds packets
back into the RX, RX MIB counters now
increment and indicate data flow.
There are RX interrupts and all indicates
(I haven't actually looked at RX packet
data) that the RX would work normally.
After switching MACCFG1[LOOP_BACK] off
no RX traffic can be seen anymore.
3 resetting the PHY (BMCR = 0x8000) and/or
restarting autoneg (BMCR = 0x1200) seems
to perform the desired action (registers
take on expected values) but still no luck
with communication all the way through
to the wire.
Especially point 2 seems to indicate that
the problem is likely to be between the
wire and the MAC somewhere but re-setting
the PHY doesn't change things. Analysis is
much complicated by the fact that there
is no documentation on the BCM5461 chip
available.
Noteworthy is also that if the system
initializes OK then it continues to work
normally; if initialization fails then
only resetting the board and restarting
helps.
I wanted to test if it makes a difference
if MotLoad used the chip prior to RTEMS
being booted (in case MotLoad did some
magic step during initialization) but
before I could really test this the
problem went away.
Big Mystery...
12/12/2007, T.S.
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