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07-22-2015 04:28 PM
In our system, we have separate WLAN and Zigbee chips. In order to complete FCC testing, we can only have 1 radio transmitting at any one time.
I noticed that there is a TX_ACTIVE signal on the EM3588 that asserts when the chip is about to start transmitting. I have a few questions regarding this signal:
1. Was this signal created with coexistence in mind?
2. Would there be any issues with using this signal to inhibit WLAN transmissions?
3. Why does the EM3588 lack any signal to inhibit zigbee transmissions?
4. Are there any WiFi modules that are designed with this coordination in mind?
Solved! Go to Solution.
07-23-2015 08:56 AM
1. TX_ACTIVE was created for any use that requires knowledge of the EM3xx device transmit state. The most common use is when using an external power amplifier, like in a front-end module (FEM). It can also be used in a managed coexistence implementation to let other devices know when it is transmitting.
2. As mentioned above, there is no issue with using this signal to inhibit WLAN transmissions. Note that Packet Trace Interface frame signal PTI_EN (PA4) can also be used to inhibit other transmissions. It is asserted while the radio is either transmitting or receiving a packet. Other radios should hold off when this signal is asserted. TX_ACTIVE can be logically OR'd or XOR'd with PTI_EN to distinguish between Tx and Rx events if needed in the management scheme.
3. Actually, the EM3588 does not lack the ability to inhibit transmissions. We recommend using EM3588 GPIO as a radio holdoff (RHO) pin to inhibit EM3588 transmissions. By default in the stack, this is PA6. When this is enabled and triggered, it will prevent the EM3588 from starting a new transmission, but it does not stop a transmission that is already in progress.
4. I believe most WiFi modules have some TX_ACTIVE signal that can be connected to the EM3588 RHO pin, but I'm not sure if they also have a hold-off pin.
As a general comment for FCC testing, you can load test firmware that should be able to easily control the transmit state of the two radios.
07-29-2015 04:37 PM
I have been trying to build in the Radio Holdoff feature into my build. It seems that this feature is dependent on using the chip in the SOC configuration, and not the NCP configuration. I say this since it appears the emRadioHoldOffIsr function definition is in a static library built for the cortex m-3 architecture (zigbee-pro-stack.a).
Is this assumption correct? I have been trying to get a proof of concept running using a Linux host machine and the EZSP UART protocol. Our final product plans on using an NCP configuration with the EZSP UART protocol.
07-30-2015 09:06 AM
The NCP has a value you can set to turn on Radio Hold Off. It is listed in UG100 as EZSP_VALUE_RADIO_HOLD_OFF (0x0E). Set the value to TRUE and you should be set.