SPIRIT1 datasheet(62/94 Pages) STMICROELECTRONICS

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Transmission and reception

SPIRIT1

62/94

Doc ID 022758 Rev 3

Another event occurs when the FIFO goes into overflow or underflow.

The overflow happens when the data in the FIFO are more than 96 bytes. The underflow

happens when the SPIRIT1 accesses the FIFO locations to read data, but there is no data

present.

For example:

●

If it reads from the RX FIFO more data than the actual number of bytes in it, the RX

FIFO underflow/overflow error occurs for an underflow event.

●

If the SPIRIT1 receives a lot of data to fill the RX FIFO and exceeds the 96 bytes limit,

an RX FIFO underflow/overflow error occurs for an overflow event.

●

If it sends more data than the actual number of bytes in the TX FIFO, the TX FIFO

underflow/overflow error occurs for an underflow event.

●

If it writes more than 96 bytes in the TX FIFO, a TX FIFO underflow/overflow error

occurs for an overflow event.

An easy way to clean the FIFOs is to use the flush commands: FLUSHTXFIFO for the TX

FIFO and FLUSHRXFIFO for the RX FIFO.

The write TX FIFO operation needs an extra SPI transaction to write correctly the last byte

into the TX FIFO. Usually, this last SPI transaction is generated from the TX command sent

to transmit the data, otherwise a dummy SPI transaction must be done.

Using the auto-retransmission feature of the SPIRIT1 (packet format STack), if the packet is

more than 96 bytes, the packet must be reloaded into the TX FIFO by the MCU. However, if

the payload is 96 bytes or less, the SPIRIT1 handles the payload and it is not necessary to

reload the data into the TX FIFO at each retransmission.

●

In addition, if the transmitter does not receive the ACK packet, the payload remains in

the TX FIFO. The user can decide to clean the TX FIFO or re-send the data again. If

the payload is more than 96 bytes, only the last part of the payload that fits the TX FIFO

remains in it.

9.10

Receiver quality indicators

The following quality indicators are associated to the received signal:

●

Received signal strength indicator (RSSI)

●

Link quality indicator (LQI)

●

Preamble quality indicator (PQI)

●

Synchronization quality indicator (SQI).

9.10.1

RSSI

The received signal strength indicator (RSSI) is a measurement of the received signal power

at the antenna measured in the channel filter bandwidth.

The measured power is reported in steps of half a dB from 0 to 255 and is offset in such a

way that -120 dBm corresponds to about 20.

RSSI reading is available after the reception of a packet in the RSSI_LEVEL register.

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