Databases
StackOverflow2013
Postsdbo
POExtract wrong data from a frame in C?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POExtract wrong data from a frame in C?
    primarykey
    data
    text
    <p>I am writing a program that reads the data from the serial port on Linux. The data are sent by another device with the following frame format:</p> <pre> <code> |start | Command | Data | CRC | End | |0x02 | 0x41 | (0-127 octets) | | 0x03| ---------------------------------------------------- </code> </pre> <p>The Data field contains 127 octets as shown and octet 1,2 contains one type of data; octet 3,4 contains another data. I need to get these data.</p> <p>Because in <strong>C</strong>, one byte can only holds one character and in the start field of the frame, it is 0x02 which means STX which is 3 characters.</p> <p>So, in order to test my program,</p> <p>On the sender side, I construct an array as the frame formatted above like:</p> <pre> <code> char frame[254]; frame[0] = 0x02; // starting field frame[1] = 0x41; // command field which is character 'A' ..so on.. </code> </pre> <p>And, then On the receiver side, I take out the fields like:</p> <pre> char result[254]; // read data read(result); printf("command = %c", result[1]); // get the command field of the frame // get other field's values </pre> <p>the command field value (result[1]) is not character 'A'. </p> <p>I think, this because the first field value of the frame is 0x02 (STX) occupying 3 first places in the array frame and leading to the wrong results on the receiver side.</p> <p>How can I correct the issue or am I doing something wrong at the sender side?</p> <p>related questions: <br /> <a href="https://stackoverflow.com/questions/2500567/parse-and-read-data-frame-in-c">Parse and read data frame in C?</a> <br /> <a href="https://stackoverflow.com/questions/2531779/clear-data-at-serial-port-in-linux-in-c">Clear data at serial port in Linux in C?</a></p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USipkiss
    plurals
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COWhat *does* the buffer contain? What function do you call to perform the read? (That is clearly not a `read` system call.) Have you verified the serial link with a terminal application?
      singulars
      1. POExtract wrong data from a frame in C?
      1. USPotatoswatter
    2. CO`STX` does not take 3 bytes; all characters take 1 byte. Some characters (like `STX`) just have longer names.
      singulars
      1. POExtract wrong data from a frame in C?
      1. USGabe
    3. COthe full code of read() function is here: http://stackoverflow.com/questions/2500567/parse-and-read-data-frame-in-c. I think so too. If I call result[1], the value should be 0x41 which means 'A', right? But it is not. I returns a strange value. Am I thinking wrong?
      singulars
      1. POExtract wrong data from a frame in C?
      1. USipkiss
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload