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PTT & OTA Requirements
#1
This is regarding the OTA protocol.

When PTT is keyed, what are the requirements?

What is required to happen if PTT is released while the preamble is being sent?

What is required to happen if PTT is released while the link setup frame is being sent?

What is the expected behavior when PTT is released while an audio stream is in progress?  Are there any requirements for how quickly the radio must stop transmitting?
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#2
Here are my thoughts,
"When PTT is keyed, what are the requirements?"
Tx admit settings should be checked. > Settings: Allways transmit, don't tx if it is valid m17 signal, don't tx if rssi is higher than xxx.

"What is required to happen if PTT is released while the preamble is being sent?"
"What is required to happen if PTT is released while the link setup frame is being sent?"
Depends on your moral codes. Since you are started to transmit some signal, you should identify yourself. I prefer saving battery and stop transmission immediately. Few milliseconds of preamble shouldn't hurt someone.

"What is the expected behavior when PTT is released while an audio stream is in progress? Are there any requirements for how quickly the radio must stop transmitting?"
We need to finish frame and transmit end of transmission signal. Otherwise codecs generally output some annoying noises.
You may pad codec input with zeros or you may directly use silent frame bytes,
uint8_t silent[] = { 0x01u, 0x00u, 0x09u, 0x43u, 0x9cu, 0xe4u, 0x21u, 0x08u }; //3200 Mode
uint8_t silent[] = { 0x01u, 0x00u, 0x04u, 0x00u, 0x25u, 0x75u, 0xddu, 0xf2u }; //1600 Mode
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