Automatically Re-Sending (Tx Auto Resend); Carrier Sensing Multi-Path Accessing (Csma) - CMOSTEK CMT2310A Manual

CMT2310A
The TX_Auto_Hop mode provides the register REQ_CHANL_LV to let users know the current channel value. Moreover, the
register FREQ_DONE_TIMES is for users to read the number of currently completed frequency hopping.
When making the configurations ready, users can set TX_AUTO_HOP_EN to 1 to enable the function, then send the go_tx
command to enter the TX_Auto_Hop mode. If requiring to stop the TX_Auto_Hop function forcedly, users can set API_STOP to 1;
then the chip detects this bit and subsequently upon the next state switching it sets API_DONE_FLAG to 1 with retaining the
current configurations, thereby, it exits TX_Auto_Hop and returns to the READY state.

7.5 Automatically Re-sending (TX AUTO RESEND)

The automatic re-sending function is an automatic control mechanism to realize the handshake between the transmitter and the
receiver. It provides two packet format fields, SEQNUM and FCS2,to judge if the handshaking between transmitter and the
receiver succeeds. These two fields are part the packet, and need to be enabled by SEQNUM_EN and FCS2_EN when the
function is used.
Its implementation principle is that: the transmitter configures the local SEQNUM and sets the NACK bit in the FCS2 field to 1 for
transmission; after the transmission is accomplished, it enters the RX state and waits for the response; when it receives the
response and finds the SEQNUM in the response packet matches the local SEQNUM and the received NACK bit is 1, the
handshaking is recognized successful.
At the receiver side, after enabling the ACK function, it enters the RX state. When the packet is received successfully, the
receiver judges whether need to answer it by the received NACK bit. If a response is needed, it enters the TX state, and the
received sequence number and NACK bit are sent back. The PKT_DONE interrupt is generated after sending back operation is
completed; then it either returns back to the state configured in RX_EXIT_STATE or remains in the RX state according to
PKT_DONE_EXIT_EN.

7.6 Carrier Sensing Multi-path Accessing (CSMA)

CSMA is a kind of conflict avoidance mechanism (speaking after sensing), that is, before transmission it senses the channel idle
status first, then determine whether to transmit or not, which helps to avoid the potential conflicts when multiple transmitters use
the same channel and increase the possibility of successful packet receiving for receivers. The key point of CSMA is comparing
the RSSI with the specified threshold to judge the channel idle status. When the channel is busy, it will repeat the procedure from
back-off to listening for several times until it finds the the channel in idle. If it fails to detect channel being idle when reaching the
repeated time limit, the corresponding interrupt and flag will be generated and transmission will be stopped. During back-off
procedure, the chip stays in SLEEP state. In the PERSISTENT mode, it will back to RFS state first and then switch to Rx state for
listening rather than back to SLEEP state. If it was under non-PERSISTENT mode, the maximum number of non-idle channels
can be configured by the CSMA_TIMES. While as if the channel was still busy, it will exit the CSMA and return to the READY
state.
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