=====
Pi433
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Introduction
============
This driver is for controlling pi433, a radio module for the Raspberry Pi
(www.pi433.de). It supports transmission and reception. It can be opened
by multiple applications for transmission and reception. While transmit
jobs are queued and processed automatically in the background, the first
application asking for reception will block out all other applications
until something gets received terminates the read request.
The driver supports on the fly reloading of the hardware fifo of the rf
chip, thus enabling for much longer telegrams than the hardware fifo size.
Description of driver operation
===============================
a) transmission
Each transmission can take place with a different configuration of the rf
module. Therefore each application can set its own set of parameters. The driver
takes care, that each transmission takes place with the parameterset of the
application, that requests the transmission. To allow the transmission to take
place in the background, a tx thread is introduced.
The transfer of data from the main thread to the tx thread is realised by a
kfifo. With each write request of an application, the passed in data and the
corresponding parameter set gets written to the kfifo.
On the other "side" of the kfifo, the tx thread continuously checks, whether the
kfifo is empty. If not, it gets one set of config and data from the kfifo. If
there is no receive request or the receiver is still waiting for something in
the air, the rf module is set to standby, the parameters for transmission gets
set, the hardware fifo of the rf chip gets preloaded and the transmission gets
started. Upon hardware fifo threshold interrupt it gets reloaded, thus enabling
much longer telegrams than the hardware fifo size. If the telegram is sent and there
is more data available in the kfifo, the procedure is repeated. If not the
transmission cycle ends.
b) reception
Since there is only one application allowed to receive data at a time, for
reception there is only one configuration set.
As soon as an application sets a request for receiving a telegram, the reception
configuration set is written to the rf module and it gets set into receiving mode.
Now the driver is waiting, that a predefined RSSI level (signal strength at the
receiver) is reached. Until this hasn't happened, the reception can be
interrupted by the transmission thread at any time to insert a transmission cycle.
As soon as the predefined RSSI level is met, a receiving cycle starts. Similar
as described for the transmission cycle the read out of the hardware fifo is done
dynamically. Upon each hardware fifo threshold interrupt, a portion of data gets
read. So also for reception it is possible to receive more data than the hardware
fifo can hold.
Driver API
==========
The driver is currently implemented as a character device. Therefore it supports
the calls open, ioctl, read, write and close.
params for ioctl
----------------
There are four options:
PI433_IOC_RD_TX_CFG - get the transmission parameters from the driver
PI433_IOC_WR_TX_CFG - set the transmission parameters
PI433_IOC_RD_RX_CFG - get the receiving parameters from the driver
PI433_IOC_WR_RX_CFG - set the receiving parameters
The tx configuration is transferred via struct pi433_tx_cfg, the parameterset for transmission.
It is divided into two sections: rf parameters and packet format.
rf params:
frequency
frequency used for transmission.
Allowed values: 433050000...434790000
bit_rate
bit rate used for transmission.
Allowed values: #####
dev_frequency
frequency deviation in case of FSK.
Allowed values: 600...500000
modulation
FSK - frequency shift key
OOK - On-Off-key
modShaping
shapingOff - no shaping
shaping1_0 - gauss filter with BT 1 (FSK only)
shaping0_5 - gauss filter with BT 0.5 (FSK only)
shaping0_3 - gauss filter with BT 0.3 (FSK only)
shapingBR - filter cut off at BR (OOK only)
shaping2BR - filter cut off at 2*BR (OOK only)
pa_ramp (FSK only)
ramp3400 - amp ramps up in 3.4ms
ramp2000 - amp ramps up in 2.0ms
ramp1000 - amp ramps up in 1ms
ramp500 - amp ramps up in 500us
ramp250 - amp ramps up in 250us
ramp125 - amp ramps up in 125us
ramp100 - amp ramps up in 100us
ramp62 - amp ramps up in 62us
ramp50 - amp ramps up in 50us
ramp40 - amp ramps up in 40us
ramp31 - amp ramps up in 31us
ramp25 - amp ramps up in 25us
ramp20 - amp ramps up in 20us
ramp15 - amp ramps up in 15us
ramp12 - amp ramps up in 12us
ramp10 - amp ramps up in 10us
tx_start_condition
fifo_level - transmission starts, if fifo is filled to
threshold level
fifo_not_empty - transmission starts, as soon as there is one
byte in internal fifo
repetitions
This gives the option, to send a telegram multiple times. Default: 1
packet format:
enable_preamble
optionOn - a preamble will be automatically generated
optionOff - no preamble will be generated
enable_sync
optionOn - a sync word will be automatically added to
the telegram after the preamble
optionOff - no sync word will be added
Attention: While possible to generate sync without preamble, the
receiver won't be able to detect the sync without preamble.
enable_length_byte
optionOn - the length of the telegram will be automatically
added to the telegram. It's part of the payload
optionOff - no length information will be automatically added
to the telegram.
Attention: For telegram length over 255 bytes, this option can't be used
Attention: should be used in combination with sync, only
enable_address_byte
optionOn - the address byte will be automatically added to the
telegram. It's part of the payload
optionOff - the address byte will not be added to the telegram.
The address byte can be used for address filtering, so the receiver
will only receive telegrams with a given address byte.
Attention: should be used in combination with sync, only
enable_crc
optionOn - an crc will be automatically calculated over the
payload of the telegram and added to the telegram
after payload.
optionOff - no crc will be calculated
preamble_length
length of the preamble. Allowed values: 0...65536
sync_length
length of the sync word. Allowed values: 0...8
fixed_message_length
length of the payload of the telegram. Will override the length
given by the buffer, passed in with the write command. Will be
ignored if set to zero.
sync_pattern[8]
contains up to eight values, that are used as the sync pattern
on sync option
address_byte
one byte, used as address byte on address byte option.
The rx configuration is transferred via struct pi433_rx_cfg, the parameterset for receiving. It is divided into two sections: rf parameters and packet format.
rf params:
frequency
frequency used for transmission.
Allowed values: 433050000...434790000
bit_rate
bit rate used for transmission.
Allowed values: #####
dev_frequency
frequency deviation in case of FSK.
Allowed values: 600...500000
modulation
FSK - frequency shift key
OOK - on off key
rssi_threshold
threshold value for the signal strength on the receiver input.
If this value is exceeded, a reception cycle starts
Allowed values: 0...255
threshold_decrement
in order to adapt to different levels of singnal strength, over
time the receiver gets more and more sensitive. This value
determs, how fast the sensitivity increases.
step_0_5db - increase in 0,5dB steps
step_1_0db - increase in 1 db steps
step_1_5db - increase in 1,5dB steps
step_2_0db - increase in 2 db steps
step_3_0db - increase in 3 db steps
step_4_0db - increase in 4 db steps
step_5_0db - increase in 5 db steps
step_6_0db - increase in 6 db steps
antenna_impedance
sets the electrical adoption of the antenna
fifty_ohm - for antennas with an impedance of 50Ohm
two_hundred_ohm - for antennas with an impedance of 200Ohm
lna_gain
sets the gain of the low noise amp
automatic - lna gain is determined by an agc
max - lna gain is set to maximum
max_minus_6 - lna gain is set to 6db below max
max_minus_12 - lna gain is set to 12db below max
max_minus_24 - lna gain is set to 24db below max
max_minus_36 - lna gain is set to 36db below max
max_minus_48 - lna gain is set to 48db below max
bw_mantisse
sets the bandwidth of the channel filter - part one: mantisse.
mantisse16 - mantisse is set to 16
mantisse20 - mantisse is set to 20
mantisse24 - mantisse is set to 24
bw_exponent
sets the bandwidth of the channel filter - part two: exponent.
Allowd values: 0...7
dagc;
operation mode of the digital automatic gain control
normal_mode
improve
improve_for_low_modulation_index
packet format:
enable_sync
optionOn - sync detection is enabled. If configured sync pattern
isn't found, telegram will be internally discarded
optionOff - sync detection is disabled.
enable_length_byte
optionOn - First byte of payload will be used as a length byte,
regardless of the amount of bytes that were requested
by the read request.
optionOff - Number of bytes to be read will be set according to
amount of bytes that were requested by the read request.
Attention: should be used in combination with sync, only
enable_address_filtering;
filtering_off - no address filtering will take place
node_address - all telegrams, not matching the node
address will be internally discarded
node_or_broadcast_address - all telegrams, neither matching the
node, nor the broadcast address will
be internally discarded
Attention: Sync option must be enabled in order to use this feature
enable_crc
optionOn - a crc will be calculated over the payload of
the telegram, that was received. If the
calculated crc doesn't match to two bytes,
that follow the payload, the telegram will be
internally discarded.
Attention: This option is only operational if sync on and fixed length
or length byte is used
sync_length
Gives the length of the payload.
Attention: This setting must meet the setting of the transmitter,
if sync option is used.
fixed_message_length
Overrides the telegram length either given by the first byte of
payload or by the read request.
bytes_to_drop
gives the number of bytes, that will be dropped before transferring
data to the read buffer
This option is only useful if all packet helper are switched
off and the rf chip is used in raw receiving mode. This may be
needed, if a telegram of a third party device should be received,
using a protocol not compatible with the packet engine of the rf69 chip.
sync_pattern[8]
contains up to eight values, that are used as the sync pattern
on sync option.
This setting must meet the configuration of the transmitting device,
if sync option is enabled.
node_address
one byte, used as node address byte on address byte option.
broadcast_address
one byte, used as broadcast address byte on address byte option.