Experimental Physics and
Industrial Control System

Sebastian Eckert via Tech-talk <tech-talk at aps.anl.gov> · Fri, 22 Dec 2023 13:59:15 +0100

Dear StreamDevice+regex experts,

I am trying to communicate with a device with a communication protocol,

where messages contain:

- 0x0D (Start of a message)

- a source and a destination byte (to assign replies to requests)

- 0x04 or 0x05 or 0x08 (read, write, data)

- address of the register to access (can be multiple bytes)

- data (can be multiple bytes, depending on data type, little endian)

- CRC16 xmodem checksum (without leading 0x0D)

- 0x0A

Before dressing the message with 0x0D and 0x0A, special characters need

to be escaped by adding a 0x5E byte before the corresponding byte and

increasing the decimal value of the byte by 64 (0x0A to 0x5E 0x4A, 0x0D

to 0x5E 0x4D, 0x11 to 0x5E 0x51, 0x13 to 0x5E 0x53, 0x40 to 0x5E 0x80,

0x5E to 0x5E 0x9E). When a message is received, the message (without the

leading 0x0D and 0x0A in the end) needs to be un-escaped in the same

fashion.

An example for reading a gain value (0x88 0x13 0x00 0x00, signed 32bit

integer, escaped: 0x88 0x5E 0x53 0x00 0x00, dec: 5000) is:

out: 0x0D 0xFF 0x03 0x04 0x01 0x03 0x07 0x02 0x74 0xA6 0x0A

in: 0x0D 0x03 0x42 0x08 0x01 0x88 0x5E 0x53 0x00 0x00 0x90 0xA1 0x0A

Here 0x01 0x03 0x07 0x02 is the address of the register we want to read.

In the reply only the first byte of the register (0x01), which was read,

is mentioned.

Below is the protocol file, in which I escape and unescape the messages

with regular expressions. It works correct for sending commands to the

device. The received messages are not un-escaped correctly. In the

example above, it just replaces the 0x5E by 0x11. My guess is that the

0x5E (^) creates the biggest problems due to its distinct role in regex.

The outcome of the byte transformation also drastically depends on the

order in which the individual un-escape regex-expressions are applied. I

would appreciate any idea of what could by the problem with the expressions.

Best regards!

Sebastian

---------proto file---------------------
Terminator = LF;

preo = 0x0D,0xFF,0x03;
prei = 0x0D,0x03,0x42;
get = 0x04;
write = 0x05;
gain = 0x01,0x03,0x07,0x02;

esco =    "%#/\x5E/\x5E\x9E/"
                    "%#/\x11/\x5E\x51/"
                    "%#/\x13/\x5E\x53/"
                    "%#/\x40/\x5E\x80/"
                    "%#/(?<!^)\x0D/\x5E\x4D/"
                    "%#/\x0A/\x5E\x4A/";

unesci =    "%#/\x5E\x4A/\x0A/"
                    "%#/\x5E\x51/\x11/"
                    "%#/\x5E\x80/\x40/"
                    "%#/\x5E\x4D/\x0D/"
                    "%#/\x5E\x53/\x13/"
                    "%#/\x5E\x9E/\x5E/";

getGain{
 out $preo $get $gain "%1.0<xmodem>" $esco;
 in $unesci $prei BS 0x01 "%#4r" "%1.0<xmodem>";
}

setGain{
 out $preo $write $gain "%#4.4r%1.0<xmodem>" $esco;
 in  $unesci $prei ETX $write 0x01 "%1.0<xmodem>";
 @init{
       out $preo $get $gain "%1.0<xmodem>" $esco;
       in $unesci $prei BS 0x01 "%#4r%1.0<xmodem>";
       }
}

----------db file---------------------
record (longin,"$(P):gain")
{
    field (DTYP, "stream")
    field (INP,  "@syncroStream.proto getGain $(PORT)")
    field (PINI,"YES")
}

record (longout,"$(P):gain_set")
{
    field (DTYP, "stream")
    field (OUT,  "@syncroStream.proto setGain $(PORT)")
}

--
Sebastian Eckert

Helmholtz-Zentrum Berlin für Materialien und Energie

BESSY II - PS-ISRR
Albert-Einstein-Str. 15
12489 Berlin
Germany

E-mail: sebastian.eckert at helmholtz-berlin.de

Tel.: +49 30 8062 14465

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System