The rgpiod daemon

rgpiod is a daemon to allow remote access to a SBC's GPIO.

Once launched the daemon runs in the background accepting commands from the socket interface.

The daemon requires no special privileges and commands may be issued by normal users.

Features

The following features are available by issuing socket commands to the daemon.

reading and writing GPIO singly and in groups
software timed PWM
GPIO callbacks
pipe notification of GPIO events
I2C wrapper
SPI wrapper
serial link wrapper
file handling
creating and running scripts

Launch options

rgpiod [options] &

-c dir	set the configuration directory (default current directory)
-l	disable remote socket interface (default enabled)
-n address	allow IP address to use the socket interface, name (e.g. paul) or dotted quad (e.g. 192.168.1.66). If the -n option is not used all addresses are allowed (unless overridden by the -l option). Multiple -n options are allowed. If -l has been used only -n localhost has any effect
-p value	set the socket port (1024-32000, default 8889)
-v	display rgpiod version and exit
-w dir	set working directory (default launch directory)
-x	enable access control (default off)

Permissions

The rgpiod daemon has an optional access control system to control access to its functions.

See Permits.

Scripts

Scripts are programs to be stored and executed by the rgpiod daemon. They are intended to mitigate any performance problems associated with the rgpiod daemon server/client model.

See Scripts.

Socket commands

Each socket command consists of a header and for commands with parameters an extension.

The header is a lgCmd_t with the following structure.

typedef struct
{
   union
   {
      uint32_t magic;
      int32_t status;
   };
   uint32_t size;
   uint16_t cmd;
   uint16_t doubles;
   uint16_t longs;
   uint16_t shorts;
} lgCmd_t, *lgCmd_p;

The magic value is 0x6c67646d (ASCII lgdm).

The size is the overall size in bytes of the optional extension.

The cmd is the command code. See the file lgSocketCommandCodes.h for the command codes.

The doubles, longs, shorts is the number of 8-byte, 4-byte, and 2-byte quantities in the extension. This information is used to network order the bytes of the message. The extension should consist of doubles 8-byte quantites, followed by longs 4-byte quantities, followed by shorts 2-byte quantities, followed by as many 1-byte quantities needed to make a total of size bytes.

If you wish to construct a client to talk to the rgpiod daemon the following are a good source of information.

rpgio.py - a Python client
rgpio.c - a C client
rgs.c - a C command line client
lgCmd.c - a useful summary of the socket commands

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(2021-01-16 21:12)