Hardware Projects » E1/T1 Hardware Interface (including icE1usb)

At least according to one of my German retronetworking books on PDH it is stated that an E1 interface must set the A[larm] bit in TS0 if no received signal is detected.

I expect we don't do that yet as we have no real concept of LOS.

Relying on the host software to insert that A bit is not really a good idea, as the host has the least idea of what's happening on the physical layer.

So I would guess, similar to the way how we automatically can generate the E bits in case of Rx CRC errors, it would be good to generate the A bits based on whether or not we see incoming Rx clock cycles.