06-08-2018 02:03 AM
Further to my question regarding the BCM53125 serial LED interface, i have looked into this more and have more questions.
The documentation for the serial LED interface does not give enough detailed information regarding the serial bit stream contents and structure to allow for me to confidently commit to a design solution.
For instance, in a system where the GMII interface is not used, 20 parallel LED displays would be available. If the user decided not to use some of the ports, or only some of the available functions, then the respective LED outputs for the disabled ports / functions would be inactive, whereas the enabled LEDs would continue to be output at their respective pins.
If the serial interface was used for driving LEDs in the same port / function configuration as above, would the serial LED interface output ONLY the active port / function data (variable bit-stream length) or would there be 'gaps' (unused bits) in the bit stream where the disabled port / function LED information would normally be (fixed bit-stream length)
Looking at the documentation, it says that the serial LED interface data source is the same as that for the parallel (on-board) LED interface (Page 119 of the Datasheet). If this is the case then i suspect that the serial LED interface bit stream MUST include the unused bits for Ports / functions that are not enabled as the chip does not differentiate between the serial LED interface and the parallel LED interface, making it a fixed length bit-stream. Is this correct?
This would mean that the serial LED interface normally operates in 2 fixed bit-length modes of operation: 20 bits for non-GMII configurations and 10 bits for GMII configurations, irrespective of any disabled port / functions. Is this correct?
This is further complicated by the addition of the WAN (Port 5) LED control. According to the datasheet, the WAN Port status can be displayed when using the serial LED interface; what affect does this have on the serial LED interface? Does it just increase the output bit length to 12 bits?
In my design i am using all Five GbE Ports, the GMII interface and the LED serial interface. For the LEDs, in addition to the GbE Port status, i want to also display the status of the WAN Port (Port 5).
LED Display Function Requirements:
For the GbE Ports (Ports 0 to 4) i want to display two LED functions - 1G/ACT and 10/100M/ACT.
For the WAN (Port 5) i want to display 1G/ACT and 10/100M/ACT.
Would the BCM53125 output EXACTLY what is configured, as shown below:
((Five GbE Ports x 2 Functions) + (One WAN Port5 x 2 Functions)) = 12bits of data clocked out?
If i then decided to configure the WAN Port (Port 5) LED registers to just display one function (1G/ACT), would the bit stream reduce to 11 bits or stay at 12, with 'gaps' in the bit-stream where the disabled function would normally be? Is the bit stream length variable or fixed?
Do you have any more information regarding the use of the serial LED interface?