Bash script to read N bytes of binary data from serial device and save them to file

Question

I am trying to write a Bash script to receive a file of known number of Bytes (we are talking about 1MB) of binary data from a serial device connected to my embedded device. These bytes must then be saved to a file for later ops.

I've tried something like (stty raw; cat > blob.bin) < /dev/ttyS0 but I would like cat to stop when it reaches the number of Bytes I am expecting, as the script needs to progress on other functions when the file is complete.

The data flow will be started from the external device and it will run continuously until the the end of the binary file from the external device.

Working on Linux Buster, unfortunately I cannot use Python or other programming languages.

Thanks!

Look at the dd command and set a block size and count.

meuh
– meuh

2020-12-12 16:54:49 +00:00
Commented Dec 12, 2020 at 16:54 — meuh
– meuh, Commented Dec 12, 2020 at 16:54

Rick · Accepted Answer · 2020-12-15 00:32:03Z

1

Thanks to the comment of @meuh, I was able to write a working script using dd:

dd ibs=1 count=$PLBYTE iflag=count_bytes if=/dev/ttyS0 of=/.../dump.bin

using dd operands count and iflag, (counting the received bytes and reading 1 byte/block) with $PLBYTE the number of expected bytes.

The script now works as expected.

Make sure to set stty in noncanonical mode (-icanon) otherwise data over 4096 bytes will be truncated and dd will not receive the expected amount of bytes.

edited Dec 15, 2020 at 0:32

answered Dec 14, 2020 at 19:51

Rick

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