Yivo

Trying to standardize the way I access sensors.

API

Part	In Checksum	Type	Description
Header		uint8_t[2]	default $K
Size	x	uint16_t	0-65,535 bytes, stored as [L,H] => `(H << 8)
Type	x	uint8_t	255 message IDs, 0 is not allowed as an ID
Data	x	uint8_t[Size]	payload data array
Checksum		uint8_t	XOR of size, type, and data bytes

0	1	2	3	4	...	-1
$	K	L	H	T	...	checksum

Byte Conversions

Type	Bytes	Format	Python	C/C++
uint8	1	B	int	uint8_t
uint16	2	H	int	uint16_t
uint32	4	I	int	uint32_t
uint64	8	Q	int	uint64_t
int8	1	b	int	int8_t
int16	2	h	int	int16_t
int32	4	i	int	int32_t
int64	8	q	int	int64_t
float	4	f	float	float
double	8	d	float	double

Todo

• Make C and python functions/objects match ... they are different right now
• Should I move to a real CRC-8 checksum?
• Remove messages from library. This is just a binary packer and not dependant on the message format other than, it is a struct
• c++: Make a header only library
• Generate C and Python messages from a template instead of writing independently
• c++: rename YivoPack_t to something else like yivopkt_t
  • Add method bool has_valid_chksum()? Class could calculate checksum and then compare to its checksum
• c++: Should I move away from std::vector and to a fixed array size, since on create of a message, I know the complete size ... it isn't a mystery at that point
  • would now have to use new and delete which aren't my favorite

Python

from yivo import Yivo, MsgInfo

# make some messages we want to send/receive
A = namedtuple("A","x y")      # id = 1
B = namedtuple("B", "x y z t") # id = 2

msgdb = MsgInfo()
msgdb[1] = ("2f", A) # 2 floats
msgdb[2] = ("4f", B) # 4 floats

yivo = Yivo(msgdb)
pkt = yivo.pack(1, A(1.,2.))

id = 0
while id == 0:
    b = serial_read() # get a byte from somewhere
    id = yivo.parse(b) # 0 or msg_id

err, msg = yivo.unpack() # err > 0 if failure to unpack

C++

• yivopkt_t: packs/unpacks (or encodes/decodes) c structs for transmission
  • uint8_t* data(): get point to buffer
  • uint16_t size(): get size of buffer
  • uint8_t msg_id(): get message id
  • void pack(id,*data,size): encode a struct to binary
  • T unpack<T>(): decode a binary message to a struct
• Yivo: basically a state machine for reading in serial data and determining when you have a message to read
  • uint8_t parse(c): read in a byte at a time and return an ID or 0
  • void get_packet(pkt): copy binary message to yivopkt_t

#include <yivo.hpp>

// some messages
struct A {int a;}; // id 1
struct B {int b;}; // id 2

Yivo yivo;

yivopkt_t pkt;
pkt.pack(1, A{1}, sizeof(A));

serial_send(pkt.data(), pkt.size()); // somehow send a message

uint8_t id = 0;
while (id == 0) {
    uint8_t b = serial_read(); // get a byte from somewhere
    id = yivo.parse(b);
}
yivopkt_t rep;
yivo.get_packet(rep);

// then decode the received message
if (id == 1) A a = rep.unpack<A>();
else if (id == 2) B b = rep.unpack<B>();

MIT License

Copyright (c) 2020 Mom's Friendly Robot Company

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.