juniorjunior/rpipwm

RPiPWM

This application was initially started to get a feel for using Pi-Blaster based Pulse Width Modulation (PWM) on the RaspberryPi. It worked so well that I ended up expanding things to work not only as an example of possible uses, but as a listening daemon for remote controlling the PWM pins. The code was written with Adafruit's analog LED strips in mind, but should be easily adaptable to any PWM functionality. Pi-Blaster is required and must be running in order to function. Caveat: This code is not hardened to attack and I do not recommend exposing the UDP interface to outside traffic without significant additional data integrity checks and rate limiters.

Building pwmdemo

• Make a build folder and change to that folder
• Run cmake against the RPiPWM folder: cmake /full/path/to/RPiPWM
• Run make

Usage

The pwmdemo app can accept multiple command line parameters. All parameters are optional and are set in the format of "--parameter[=value]":

Parameter	Values	Description
--id	0 - 64	The ID of this client/target. This value defaults to 0 (zero) which means "act on all messages regardless of intended target".
--test	none	Bind to /dev/null instead of /dev/pi-blaster when setting color values. Useful for testing.
--daemon	none	Only listen for UDP messages. The keypress and display thread is not started.

Setup

• GPIO Pins - The code has three pins (defaults to 23, 24, 25) set up as Red, Green, and Blue respectively. These are the GPIO numbers not the connector pin numbers. They are set at the top of the source and do require a recompile if changed.

UDP Messages

Each message consists of two four byte (32 bits) unique numbers used as a basic packet filter, four bytes (32 bits) for the message ID, a one byte (8 bits) command, four bytes (32 bits) for the target ID, followed by the appropriate data for the message type. Multiple targets can have the same ID. A target ID of 0 means "all targets".

The first and second four byte integers values are 4039196302 and 3194769291 respectively. The packet filter values are used to do a simple check that the incoming packet is meant for the device receiving it. Slow speed receivers may crash or hang if over-flooded with UDP packets. Since the receiver must listen for broadcast UDP there is a decent liklihood that other traffic may show up. Having a specific 64 bits of data at the very start of the packet drastically reduces the chance of thinking the packet needs to be processed which saves major clock cycles on slow receivers. If there is a better/simpler/more efficient way of doing this I'm open to suggestions.

Name	Value	Description
CMD_OFF	0x00	Turn off all colors (i.e. terminate auto patterns and set values to zero)
CMD_SETLEVELS	0x01	Message contains data to set one full color triplet (R,G,B) and rest value
CMD_AUTOPATTERN	0x02	Message contains data containing a ramp time along with NumColors number of color triplets to cycle between.
CMD_AUTODISABLE	0x03	Message contains only the command (no extra data) and stops any current auto-cycling pattern.

CMD_OFF

Name	Description	Type	Bits
Filter_1	Value: 4039196302	Unsigned Int	32
Filter_2	Value: 3194769291	Unsigned Int	32
MessageID	This is used to identify and ignore duplicate messages. Due to the unreliable nature of UDP, and the slow embedded processors, sending multiple duplicate messages some few milliseconds (10) apart can help ensure the devices get all their messages	Unsigned Int	32
CMD	This is the command action to take	Unsigned Char	8
TargetID	This is the target ID for the broadcast message.	Unsigned Int	32

CMD_SETLEVELS

Name	Description	Type	Bits
Filter_1	Value: 4039196302	Unsigned Int	32
Filter_2	Value: 3194769291	Unsigned Int	32
MessageID	This is used to identify and ignore duplicate messages. Due to the unreliable nature of UDP, and the slow embedded processors, sending multiple duplicate messages some few milliseconds (10) apart can help ensure the devices get all their messages	Unsigned Int	32
CMD	This is the command action to take	Unsigned Char	8
TargetID	This is the target ID for the broadcast message.	Unsigned Int	32
RampTime	This is the time in milliseconds over which the color will be changed	Unsigned Int	32
Red	This is the level for the "red" GPIO pin. Values from 0.0 to 1.0	Unsigned Char	8
Green	This is the level for the "green" GPIO pin. Values from 0.0 to 1.0	Unsigned Char	8
Blue	This is the level for the "blue" GPIO pin. Values from 0.0 to 1.0	Unsigned Char	8

CMD_AUTOPATTERN

The CMD, RampTime and NumColors value/bits are at the head of the message. The number of color triplets (R, G, B, RestTime) passed must be equal to NumColors.

Name	Description	Type	Bits
Filter_1	Value: 4039196302	Unsigned Int	32
Filter_2	Value: 3194769291	Unsigned Int	32
MessageID	This is used to identify and ignore duplicate messages. Due to the unreliable nature of UDP, and the slow embedded processors, sending multiple duplicate messages some few milliseconds (10) apart can help ensure the devices get all their messages	Unsigned Int	32
CMD	This is the command action to take	Unsigned Char	8
TargetID	This is the target ID for the broadcast message.	Unsigned Int	32
RampTime	This is the time in milliseconds over which the color will be changed	Unsigned Int	32
NumColors	This is the number of color triplets in the message	Unsigned Char	8
Red	This is the level for the "red" GPIO pin. Values from 0.0 to 1.0	Unsigned Char	8
Green	This is the level for the "green" GPIO pin. Values from 0.0 to 1.0	Unsigned Char	8
Blue	This is the level for the "blue" GPIO pin. Values from 0.0 to 1.0	Unsigned Char	8
RestTime	This is the time in milliseconds to hold on this color after ramping	Unsigned Int	32

CMD_AUTODISABLE

Name	Description	Type	Bits
Filter_1	Value: 4039196302	Unsigned Int	32
Filter_2	Value: 3194769291	Unsigned Int	32
MessageID	This is used to identify and ignore duplicate messages. Due to the unreliable nature of UDP, and the slow embedded processors, sending multiple duplicate messages some few milliseconds (10) apart can help ensure the devices get all their messages	Unsigned Int	32
CMD	This is the command action to take	Unsigned Char	8
TargetID	This is the target ID for the broadcast message.	Unsigned Int	32