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IMU sample fetching over RS485

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Old 07-23-2008
IMU sample fetching over RS485
Hi,

I'm writing a program that will take the byte values put out by an IMU and perform the integrations to find position.

Right now, I am only concerned with how to properly recieve the data from the IMU. I can worry about the integrations and things later. The IMU will connect to my laptop via an RS422 port to USB converter for testing. Ultimately, it will be connected to a Linux processor board with a RS485 port.

The data stream from the IMU runs at 115200 Baud and each sample is 37 bytes long. The first four bytes are sync bytes, with a lot of other bytes with a 8-bit checksum at the end.

What I would like to do is to get a 37 byte sample starting at the synchronization bytes and first use the checksum to validate the data. Then I would like to strip away all of the bytes except for the Timer bytes, Gyro Bytes, Accelerometer Bytes and Magnetometer Bytes. Then I will store these bytes so that I can start the integrations.

This code will be part of a larger program later on so it cannot run within a while loop, but for now it would be fine for my testing purposes on my laptop. I don't need to get every sample coming over the serial port, I just need to make sure that I get a full sample and not partial.

I've done low datarate stuff over the RS232 port, but RS485 is different and this is a faster datarate. I am thinking about using some low priority interrupt to get a 37 byte sample every so often and store the byte values.

Does anyone know how I would approach this?

Thank you,
aloha_boi
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LEARN ABOUT DEBIAN

sample

SAMPLE(3alleg4) 						  Allegro manual						   SAMPLE(3alleg4)

NAME

       SAMPLE - Stores sound data. Allegro game programming library.

SYNOPSIS

       #include <allegro.h>

       typedef struct SAMPLE

DESCRIPTION

	  int bits;		      - 8 or 16
	  int stereo;		      - sample type flag
	  int freq;		      - sample frequency
	  int priority; 	      - 0-255
	  unsigned long len;	      - length (in samples)
	  unsigned long loop_start;   - loop start position
	  unsigned long loop_end;     - loop finish position
	  void *data;		      - raw sample data

       A  sample  structure, which holds sound data, used by the digital sample routines. You can consider all of these fields as read only except
       priority, loop_start and loop_end, which you can change them for example after loading a sample from disk.

       The priority is a value from 0 to 255 (by default set to 128) and controls how hardware voices on the  sound  card  are	allocated  if  you
       attempt	to play more than the driver can handle. This may be used to ensure that the less important sounds are cut off while the important
       ones are preserved.

       The variables loop_start and loop_end specify the loop position in sample units, and are set by default to the start and end of the sample.

       If you are creating your own samples on the fly, you might also want to modify the raw data of the sample pointed by the  data  field.  The
       sample  data  are  always  in  unsigned format. This means that if you are loading a PCM encoded sound file with signed 16-bit samples, you
       would have to XOR every two bytes (i.e. every sample value) with 0x8000 to change the signedness.

SEE ALSO

       load_sample(3alleg4), exsample(3alleg4)

Allegro 							   version 4.4.2						   SAMPLE(3alleg4)