S2-LP datasheet(61/90 Pages) STMICROELECTRONICS

61 / 90 page

S2-LP

Link layer protocol

DocID029944 Rev 1

61/90

Link layer protocol

8.1

Automatic acknowledgment

The automatic acknowledgment embedded in the S2-LP allows the receiver to send back

to the transmitter an ACK packet to confirm the reception of a packet. The automatic

acknowledgement must be configured in receiver side by setting the register

AUTO_ACK = 1b.

In transmitter side, the ACK request must be set according the NACK field of the packet:

when the register NACK = 0b the NO_ACK field is ‘0’ that represents an ACK request.

Once the transmitter has sent a packet with an ACK request, it will wait for the ACK packet

using the usual RX configuration: so the RX timer must be set according to the data rate,

as well the receiver channel filter bandwidth and SQI. If the transmitter does not receive

any ACK packet when it must, the packet transmitted is considered lost, and there is no

TX_DATA_SENT IRQ notification.

The ACK packet sent is formatted as follows:



The destination address field shall be set equal to the source address field of the

received packet.



The source address field shall be filled with content of register TX_SOURCE_ADDR.



The sequence number of the ACK packet will be the same as the received packet.



The control field shall be set accordingly to any pre-negotiated configuration.



The main controller shall check if the PIGGYBACKING bit flag is set:



If it is set, it will check if there is any data in the TX FIFO: if found, it shall be

transmitted in the payload field



If any of the above checks fail, no payload shall be transmitted: an empty packet is

sent which contains only the source and destination addresses and the sequence

number of the packet being acknowledged. Anyway, the TX FIFO will be read at list

once, consequently generating an underflow condition in case of empty FIFO. To clear

the FIFO, a FLUSHTXFIFO command is needed.



The NO_ACK flag shall be set to ei

ther to ‘1’ (no explicit acknowledgment).

An ACK packet is considered receiveda if and only if it is not discarded for RX

timeout, or filtered and its sequence number match that of the sent packet.

If the automatic acknowledgment is enabled (receiver side), the TX command is not

supported and must not be used.

In case of packet with fixed payload length, since the ‘empty packet’ will not contain any

payload (as PIGGYBACKING bit is not set), the receiver could not be able to de-frame the

packet. So the packet option having fixed payload length but no piggybacking is not

supported by S2-LP.

The S2-LP device cannot operate at the same time in Auto-Acknowledge and Auto-Re-TX

modes (only one at a time).

The automatic acknowledgement is supported only for STack packet format.

a There is no explicit way to signal that a packet is an ACK packet or not. If, after having sent a packet requiring

acknowledgement, the transmitter receives a packet from the receiver with the same sequence number, it shall

assume that this is an ACK packet.

S2-LP 数据表(PDF) 61 Page - STMicroelectronics

S2-LP 数据表(HTML) 61 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

数据表下载