This document describes the BlueNRG-LP 2.4 GHz radio proprietary low-level driver, which provides access to the BlueNRG-LP
device in order to send and receive packets without using the Bluetooth link layer. An application using a central data structure
and APIs can control dif
ferent features of packets such as: interval, channel frequency, data length and so on.
UM2726 - Rev 2 - March 2021
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1BlueNRG-LP radio operation
The BlueNRG-LP 2.4 GHz radio low level driver interface controls 2.4 GHz radio. Furthermore, it interacts with the
wake-up timer, which runs on the slow 32 kHz clock, the RAM memory and the processor.
RAM is used to store radio settings, the current radio status, the data received and data to be transmitted. The
radio low level driver can manage up to 8 dif
Several features are autonomously managed by the radio, without intervention of the processor:
•Packet encryption
•Communication timing
•Sleep management
A number of additional features are present and they are specifically related to the Bluetooth low energy standard
like the Bluetooth channel usage.
ferent radio configurations also called state machines.
UM2726
BlueNRG-LP radio operation
UM2726 - Rev 2
page 2/29
2Data packet format
Preamble
NetworkID
Header
DataCRC
BlueNRG-LP
1 byte4 bytes1 byte
0 - 255 bytes
3 bytes
Length
1 byte
There is only one packet format used in the BlueNRG-LP, it is shown below.
A packet consists of six fields which, only four are user-accessible:
•By default, the preamble is 1-byte long. But, the user can define how many times to repeat the preamble
through RADIO_SetPreambleRep().
•
NetworkID is the address of the device, expressed in 4 bytes. The receiver device accepts only those
packets whose NetworkID field is the same as the one in its own address. The NetworkID should satisfy the
following rules:
–It has no more than 6 consecutive zeros or ones
–It has not all 4 octets equal
–It has no more than 24 transitions
–It has a minimum of 2 transitions in the most significant 6 bits
The NetworkID field is user-accessible through API RADIO_SetTxAttributes() or API
HAL_RADIO_SetNetworkID().
•Header can accept any values and its length is 1 byte. It can be used as a byte of data, but no encryption is
applied to this field.
•Length represents the length of the data field. The user sets this value for a packet to transmit or reads this
value from a received packet.
The maximum number of bytes of the payload (with or without encryption) that the BlueNRG-LP link layer
can accept in reception is 255. The user can set the value of this threshold (from 0 to 255) at hardware level
through API RADIO_SetMaxRecievedLength().
Then, the maximum value of the length field is 255 for the BlueNRG-LP, with some exceptions. If the
encryption is enabled, at the maximum length of the data field, it must subtract 4 bytes. These 4 bytes are
reserved for the MIC field added to the packet as shown in Figure 2. Packet format with encryption enabled.
Packet format with encryption enabled. The table below contains a summary about the length field.
UM2726
Data packet format
Figure 1. Packet format
UM2726 - Rev 2
Data channels
BlueNRG-LP255251255251
To avoid memory corruption due to bad length field received (in packet where the CRC check fails), the user
must reserve the maximum memory for packet received that includes 2 bytes of header field as well as the
data field
Table 1. Values in bytes for the length field
Data channels with
encryption
Advertising channels
Advertising channels
with encryption
page 3/29
Preamble
NetworkID
Header
DataCRC
BlueNRG-LP1 byte4 bytes1 byte
0 - 251 bytes
3 bytes
Length
1 byte
MIC
4 bytes
UM2726
Data packet format
•Data can accept any value and its length is decided by the length field. The user defines a memory buffer in
order to set the header field, the length field and data field as follows:
PacketBuffer[0] = 0x01; // Header field
PacketBuffer[1] = 5; // Length field
PacketBuffer[2] = 0x02; // Data byte 1
PacketBuffer[3] = 0x03; // Data byte 2
PacketBuffer[4] = 0x04; // Data byte 3
PacketBuffer[5] = 0x05; // Data byte 4
PacketBuffer[6] = 0x06; // Data byte 5
If the encryption is enabled, only the data field is encrypted. The other fields including the header field and
the length field are not encrypted.
•
The CRC is used to identify corrupted packets. Its length is 3 bytes and the radio generates and checks
it during transmission and reception respectively
calculation, except in the advertising channels where the initial value is set to 0x555555. The CRC hardware
feature can be disabled. It means that the hardware neither appends the CRC in transmission nor checks it
during reception.
Figure 2. Packet format with encryption enabled
. The user can configure the initial value for the CRC
UM2726 - Rev 2
page 4/29
3Radio low level driver framework
3.1Description
The radio low level driver consists of four files:
•
bluenrg_lp_ll_radio.h
bluenrg_lp_ll_radio.c
•
•bluenrg_lp_hal_radio.h
•bluenrg_lp_hal_radio.c
3.2API architecture
The radio low level driver interface provides a set of APIs (file bluenrg_lp_ll_radio.c) which allows the following
functions to be addressed :
•
Radio initialization
•
Encryption
•Set receiver and transmitter Phy (1 Mbps, 2 Mbps, S = 2, S = 8)
•Communication channel management
•Set the network ID, CRC initial value, power level
•Set the maximum received packet length and the receive timeout
•Test commands (tone)
List of APIs managing these settings are:
•RADIO_Init()
•RADIO_SetEncryptionCount()
•RADIO_SetEncryptionAttributes()
•RADIO_SetEncryptFlags()
•RADIO_EncryptPlainData()
•RADIO_Set_ChannelMap()
•RADIO_SetChannel()
•RADIO_SetTxAttributes()
•RADIO_SetBackToBackTime()
•RADIO_SetTxPower()
•RADIO_SetReservedArea()
•RADIO_MakeActionPacketPending()
•RADIO_SetPhy()
•RADIO_SetMaxRecievedLength()
•RADIO_SetPreambleRep()
•RADIO_SetDefaultPreambleLen()
•RADIO_DisableCRC()
•RADIO_StopActivity()
•RADIO_StartTone()
•RADIO_StopTone()
Most of the APIs modify the parameters of the state machine passed as parameter. On the other hand, some
parameters are global, that is they are valid for all the state machines. One of which is the receive timeout
that is set calling RADIO_SetGlobalReceiveTimeout(). This value sets the duration of the receive window in
microseconds.
The radio low level driver uses a central data structure that consists of a linked list of ActionPackets. An
ActionPacket is a structure (C language) that, in conjunction with the APIs above, defines a complete operation of
transmission or reception. It also includes a number of callbacks, which allow the user to define a chain of actions.
UM2726
Radio low level driver framework
UM2726 - Rev 2
page 5/29
UM2726
API architecture
The ActionPacket is composed of input fields used to configure the action and output fields holding information on
the action once it has been executed. The table below contains the information on these fields.
Table 2.
Parameter nameInput/outputSummary
StateMachineNoIN
ActionTagIN
MaxReceiveLengthIN
W
akeupTimeIN
*next_trueIN
*next_falseIN
(*condRoutine)
(ActionPacket*)
(*dataRoutine)
(ActionPacket*, ActionPacket*)
*dataIN/OUT
timestamp_receiveOUT
statusOUTThe status register with the information on the action.
rssiOUTThe RSSI of the packet was received with. RX only
ActionPacket structure
This parameter indicates the state machine number for
this action. From 0 to 7
The configuration of the current action.
Details of the flags in the ActionTag table
Set the maximum number of bytes that the link controller
accepts in reception. It is between 0 and 255 byte
Contains the wake-up time in microseconds if it is
relative. If it is absolute, the time is expressed in system
time units (STU). More about STU can be found in the
BlueNRG-LP timer module application note
Pointer to next ActionPacket if condRoutine() returns
TRUE
Pointer to next ActionPacket if condRoutine() returns
F
ALSE
IN
INUser callback to manage data
User callback necessary to decide the next action in a
linked list of ActionPackets. The routine is time critical
and it must end within 45 us.
Pointer to the array with the data to send (header
and data field), for TX.
Pointer to the array where the data received are copied,
for RX. In case of RX, the array must have the max. size
as explained in Section 2 Data packet format
This field contains the timestamp when a packet is
received. It is intended to be used in the dataRoutine()
callback routine. RX only
It is expressed in STU. One STU is 625/256
microseconds.
, length
.
.
UM2726 - Rev 2
The ActionTag is a bitmask used to enable different features of the radio, used by the ActionPacket. The table
below explains these parameters.
page 6/29
Table 3. ActionTag field description
BitNameDescription
This bit sets where the position of the timestamp is taken, at
the beginning of the packet or at the end of it.
7TIMESTAMP_POSITION
6INC_CHAN
5RELATIVE
4WHITENING_DISABLE
3RESERVEDRESERVED
2TIMER_WAKEUP
1TXRX
0PLL_TRIG
1. In the advertising channels, the frequency hopping is limited to 1 hop.
0: end of the packet, when the demodulator receives the last
bit of the packet received or when the last transmitted bit has
been shifted out from the transmit block.
1: beginning of the packet, when the demodulator detects the
preamble + access address. Rx only
This bit activates automatic channel increment. The API
RADIO_SetChannel()
0: no increment
1: automatic increment
It determines if the WakeupTime field of the ActionPacket is
considered as absolute time or relative time to the current.
0: absolute
1: relative
This bit determines whether whitening is disabled or not
0: whitening enabled
1: whitening disabled
In the Radio handler, this bit determines if the action (RX or
TX) is going to be executed based on the back-to-back time
or based on the W
If it is the first action, this bit is ignored since it is going to be
executed always based on the WakeupTime.
0: based on the back-to-back time (default 150 µs).
1: based on the WakeupTime
This bit determines if the action is an RX action or a TX
action.
1: TX action
0: RX action
This bit activates the radio frequency PLL calibration.
0: radio frequency calibration disabled.
1: radio frequency calibration enabled.
User should set this in the first action
(1)
sets the value of the increment.
ime.
akeupT
UM2726
API architecture
UM2726 - Rev 2
The bits of the status field of the ActionPacket represent the map of the interrupts triggered by the last radio
action. A description of the status field of the ActionPacket is reported below. Refer to "the BlueNRG-LP radio
controller" reference manual (RM0480) for the full details.
page 7/29
Table 4. Status_table
Bit nameBit positionDescription
RCVOK31Receive data without errors.
RCVCRCERR30
TIMECAPTURETRIG29Time captured in Time Capture register.
RCVCMD28Received command.
RCVNOMD27Received MD bit embedded in the PDU data packet header was zero.
RCVTIMEOUT26Receive timeout (no preamble found).
DONE25Receive/Transmit done.
TXOK24Previous transmitted packet received OK by the peer device.
RCVLENGTHERROR18The received payload length exceed the maximum.
PREVTRANSMIT6Previous event was a Transmission (1) or Reception (0).
This error is raised only if at least preamble and access address have been detected.
Receive data fail (CRC error).
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API architecture
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page 8/29
4How to write an application
HAL_RADIO_API
Relative Time
TX or RX
start
There are two ways to write an application: the former is based on the HAL layer composed mainly of four APIs,
and the latter based on the use of the ActionPacket data structure.
4.1HAL layer approach
The simplest way is to use a set of APIs provided in HAL radio driver (file bluenrg_lp_hal_radio.c), that allows the
radio to be configured to fulfill the actions below:
•Send a packet
Send a packet and then wait for the reception of a packet (ACK)
•
•Wait for a packet
•Wait for a packet and if the packet is received, a packet is sent back (ACK)
In this contest, the user does not need to use the ActionPacket to configure the operations of the radio, but a
pointer to a user callback is requested, which handles different information according to the executed action:
•TX action: IRQ status
•RX action: IRQ status, RSSI, timestamp and data received
The user callback is called in interrupt mode, in particular in the BLE_TX_RX_IRQHandler(), that has the
maximum priority.
The second parameter of each API is a relative time in microseconds that represents when the next radio activity
starts from the moment in which the API is called. This delay must be big enough as otherwise it is not possible to
program the radio timer and an error code is returned.
The user can choose the desired time without taking into account the time that the radio uses for its setup. Then,
the delay that is passed to the API, represents when the first bit is transmitted or the receive window starts.
UM2726
How to write an application
Figure 3. Relative time
UM2726 - Rev 2
page 9/29
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