===== Pi433 ===== 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.