ksz8041 PHY chip for 52259

[neil]

Hi Mark,
  Just wondering if you can give me your thought on this, as I have never dealt with a PHY chip before. The demo kit has the KSZ8041NL , but I can only get the KSZ8041TLI part. The only difference I can see is that the TLI part also does SMII interface, package type, and about £1 more expensive. Apart from that is looks compatible , all registers numbers in the NL are the same as the TLI, the only thing the TLI has a couple of extra registers for cable diagnostics. 

Thanks very much for your help
Regards
Neil

[mark]

Hi Neil

Check also the KS8721 or the Davicon DM9161AE.
Basically all PHYs have a standard set of registers and so are basically interchangeable. Therefore all will be OK for normal Ethernet connectivity.

The differences are in the additional features that they support (like auto crossover or IEEE I588 PTP capability in the Nat-Semi DP83640). If the extra features are not activated they all look much the same.

Regards

Mark

[neil]

Hi Mark,
  Thanks for your help . I managed to get 22 of the KSZ8041TLI part, so will use this. I had a look at the DEMO kit that uses this, and noticed the reset pin only seems to go to the edge connectors, and doesnt have any pullups, so going no where.  I fully understand that really this is not a utasker issue, but any help is really great.

Regards
Neil

[mark]

Hi Neil

See whether there is an internal pull up on the reset line.

If you do have a spare port which can be used to take the PHY out of reset it is a good idea to use it to control this.
The PHYs have weak internal pull-ups and pull-downs on several 'STRAP' inputs which define its mode on reset. These share other lines and sometimes these have to be connected to the processor which may have a weak internal pull-up. In this case it is not always sure which state the configuration gets.

See following: http://www.utasker.com/forum/index.php?topic=161.0

When the processor can control the reset it can:
a) hold the PHY in reset
b) set the lines temporarily as outputs and drive the required state
c) allow the PHY to come out of reset
d) set the pins back to MII mode


Also external resistors do the trick but the SW version is more flexible.

Regards

Mark

[neil]

Hi Mark,
  Do you recommend controlling all STRAP inputs with the processor?
 
  Is it okay to drive the KSZ8041TLI strap inputs and RESET pins directly from the processor pins?

Regards

Neil

[mark]

Hi Neil

It depends on the PHY chip.

The inputs which share with the MII interface are the ones to watch (they are already connected to the processor because you have no choice). The others can be strapped in HW.
As long as you can communicate with the PHY via the serial bus (the ones muxed with IRQ3 and IRQ5) you can then overwrite most strap settings - on order to communicate, you need to ensure that you know the PHY address, which is strapped. If it is strapped via a line which is not well defined (the ones discussed earlier) you can either ensure it by driving (as discussed earlier) or else scan all possibilities until the used address has been found (I have done this on the M52259EVB because there seems to be a pull-up/pull-down issue on its address strapping lines (although it still seems to get 0x01 as value - but best to be safe).
Some PHYs may also need a delay (not the Micrel ones as far as I know and have experienced) before they are ready in which case they can be polled until a register read returns the expected value.

regards

Mark

[neil]

Hi Mark,
  As I never have used an PHY directly before there are a few things Im not sure about.

1. Looking at the 52259 manual,is the MII the interface for setting up the PHY?
2. What actual pins to I need to have HW pulldown/up etc?
3. How do I communicate with the device when setting it up?

I have attached the strapping inputs.

Regards
Neil

[mark]

Hi Neil

The MII interface has two parts.
- The communication part with is effectively interfaced via the M52259 ports TI and TJ
- The maintenance channel (a two wire bus like an SPI) interfaced on pins IRQ3 and IRQ5. This is optional and always reading and writing to PY internal registers.

You need pullups/down only on the strap inputs. However if you read the PHY details about these pins you will find that they usually have weak internal pullups/downs to set the most usual settings (eg. MII mode, auto-negotiation).
Compare with the M52259DEMOCOM diagram where the straps have all been externally pulled up/down (maybe some could be spared?)
The KSL8041 is not difficult to strap since it doesn't share any strap inputs with the MII bus and so there are no ports which will possibly conflict.

Communication takes place over the maintenance interface. In the M5223X project the routines fnMIIread() and fnMIIwrite() are used for this. In the M5225X project these are also used but, instead of being internally connected to the internal EPHY) they are connected externally with the external PHY. (FEC_MCD and FEC_MDIO). Note that these have external pull-ups on the M52259DEMO COM board and probably need these (the MDIO is bi-directional and normally open drain - it operates at 2.5MHz and so 3k3 pull up is a good choice).

Regards

Mark

[neil]

Hi Mark,
  I understand things better regarding the PHY,thanks for all your time explaining this, cheers.

I know the 52235 had problems with auto-negotiation , I assume this is not an issue with external PHY now?

Was the internal PHY a big cause for the 5223x chip for being so hot?

Thanks again
Neil

[mark]

Hi Neil

The external PHYs have no such problems with auto-negotiation.
Also the M52259 runs much cooler because the EPHY causes the M5223X it to get quite hot.

Regards

Mark

[neil]

Hi Mark,
   Thanks for all your help on this part, just a few more questions if thats ok?

1. I will copy the pull downs as in M52259DEMOCOM diagram (there are no external pullups), and connect reset pin to processor i/o pin, this fine?.

2. MDIO/MDC pins not in strap input, but pulled low on M52259DEMOCOM diagram. Is it best to copy this?

3. I notice on the M52259DEMOCOM diagram there are no external pullups on NWAYEN for auto negotiation, and SPEED for 100Mbps. Does the M52259 change this in software , depending on the value in NETWORK_PARAMETERS.usNetworkOptions during initialisation?

4. As the reset pin will be connected to an io pin, is it best to have a pull up resistor on this so it comes out of reset when power is applied?

5. Does the PHY get the MAC and ip address from the M52259? If so, then does the PHY only pass info to 52259 that has matching MAC and IP address?

6. If I have to reset the device, what part of the initialisation is this done? And if so is there anything to send to it through the  fnMIIwrite() commands to initialise it?

Thanks again Mark
Neil

[mark]

Hi Neil

1. Be careful RN2 is a pull-up so there are some pull-ups involved. Reset to I/O is not really necessary with the Micrel since there are no conflict possibilities, but it won't hurt to be able to control it.
2. Also here these are pull-ups and not pull-downs. Pull ups are necessary - at least on the data line.
3. The LEDs act as pull-ups. In any case, all default settings (apart from address) can be changed later via the management interface. Then the final setting is defined by parameters.
4. It doesn't really matter whether the PHY comes out of reset immediately or only then when programmed, but check the RESET timing to ensure that the reset is held long enough to be reliable.
5. The PHY does not MAC / IP filtering. All of this is done in the MAC. The PHY is converting pulses on the LAN to digital data and its function is essentially analog and has no digital intelligence (apart from negotiation and possible additional functions)
6. When the device is reset it reads the strap inputs and uses these settings. Changes to the strapped settings can then only be performed via the fnMIIWrite() commands. Normally a reset after initialisation is never required. It is also possible to command a soft reset via management interface.

Regards

Mark

[neil]

Hi mark,
  Thanks for help. I never noticed RN2 was a pull up 

I notice that on the M52259DEMOCOM, the reset pin is not connected to anything, and doesnt seem to have an internal pullup going by the data sheet. How is this dealt with on the M52259DEMOCOM board?

Neil

[mark]

Hi Neil

This line is driven from the MCU board which has a pull-up resistor 4k7 and also a RESET LED to 3V3. When the reset output of the Coldfire is active it drives this from U3. See page 3 of the DEMO MCU circuit diagram.

Regards

Mark

[neil]

Hi Mark,
  Thanks, I never saw that. I guess I can just do this instead using a io pin.

Neil