CN104270550A - A reliable transmission method of image data based on CAN bus - Google Patents

Abstract

The invention discloses a reliable image data transmission method based on a CAN bus. The method is based on a CAN expansion frame format and conducts dynamic secondary division based on row data, sequence matching, consistency checkout, error handling and the like on the image data blocks transmitted on the CAN bus so that transmission reliability can be improved, and data integrity can be guaranteed. By means of the method, the image data with the transmission height being 65536 pixels and the width being 65536 pixels can be transmitted at most, and great help is provided for expanding application of the CAN bus.

Description

A reliable transmission method of image data based on CAN bus

technical field

The invention belongs to the technical field of data transmission and relates to a reliable transmission method for sending image data from a data sender to a data receiver based on a CAN bus. the

the

Background technique

CAN bus communication technology is widely used in comprehensive automation control systems in various fields. Its advantages of high reliability, strong anti-interference, simple development, low cost, short frame transmission and non-destructive arbitration technology make it widely used. But CAN itself is not a complete protocol, it only includes the physical layer and the data link layer, two underlying protocols, and high-level protocols need to be further developed for high-efficiency communication. In the current development of the CAN bus, the transmission method for large data blocks is usually based on the basic communication protocol, or fixed-length segmentation for massive data. This brings a lot of inconvenience to the transmission of data blocks of varying sizes in practical applications, especially for data such as images, which not only requires a fast transmission rate, but also requires the order, correctness and integrity to be guaranteed.

In the invention patent (publication number: CN 1706170A) of R. Schulmans et al. "Method for transmitting data on the bus", it focuses on the data transmission based on the communication standard format. The invention patent is only based on the standard frame data field The length of the data is divided once, because only the consistency verification of the number of bytes is carried out, so that the data has not been verified more completely. Not only that, the number of data in this invention is given by the receiver, and the sender is only a control circuit, and the receiver is only a computer, thus limiting the direction of transmission.

The invention patent of Jiang Kai et al. (publication number: CN 101552785A) "CAN bus communication protocol for mass data transmission based on message mechanism" focuses on a CAN bus communication protocol for mass data transmission based on message mechanism. Only when the number of data bytes is greater than 65536, the invention patent adopts the secondary division processing of the packing method. If the data is wrong, the whole packet retransmission according to this communication protocol design will waste a lot of bandwidth, and the data smaller than 65536 bytes cannot be effectively processed.

the

Contents of the invention

In order to solve the above-mentioned technical problems, the present invention provides a reliable transmission method for sending image data from one data sender to a data receiver based on the CAN bus. The dynamic secondary division, each sending a line returns a line sending status frame to improve the rate and reliability of CAN bus transmission.

The technical solution adopted in the present invention is: a reliable image data transmission method based on CAN bus, which is applied to a system with one master and multiple slaves. There is only one master device, which is the system management computer, and the number of slave devices is determined by actual needs. The data transmission is carried out between the master device and the slave device, and there is no mutual transmission between the slave devices; it is characterized in that it includes the following steps:

Step 1: The image data sender first performs dynamic secondary segmentation processing based on row data on the image data block transmitted on the CAN bus according to the size of the image data object, that is, first divides the image data into several data blocks according to the number of rows, Then divide the pixel color information in each data block into a multi-frame form of several data frames according to a specific frame format;

Step 2: The image data sender sends the size information frame to the image data receiver;

Step 3: After the image data receiver receives the size information frame, it returns the sending status information to the image data sender, that is, the response data frame, and judges:

If the return information received by the image data sender is successful, the following steps 4 are performed in sequence;

If the return information received by the image data sender is failure, then go back to step 2;

If the sender of the image data waits for 1s and does not receive the return information, then go back to step 2;

Step 4: The image data sender sends one line of data to the image data receiver in sequence;

Step 5: After receiving a row of data, the image data receiver checks the order and content of all data frames, returns the sending status information to the image data sender according to the inspection results, and sends the status frame immediately, and judges:

If the return information received by the image data sender is successful, then perform the following step 6 in sequence;

If the return message received by the sender of the image data is failure, resend the image data of the row after the frame number according to the returned error coordinate number;

If the sender of the image data waits for 1 second and does not receive the return information, it will turn around and execute the above step 4, and automatically resend the data frame of the line; if it has not received the return information after resending three times, it will be judged as a failure and stop sending , self-reset the CAN bus, and make the CAN bus continue to resend the row of data frames;

Step 6: Send subsequent lines of image data sequentially according to the method described in step 5, until the number of lines of image data correctly received is equal to the number of lines in the size information frame, and the transmission of image data is completed.

Preferably, the specific frame format described in step 1 includes an arbitration field, a control field, and a data field; the identifier in the arbitration field uses an extended 29-bit identifier, including a priority control bit, a source address , target address, function number, and pixel row coordinate X; according to the frame priority, the identifier with the lowest binary number has the highest priority, so define ID28 and ID27 as priority control bits, and 00 as size information frame priority Level, 01 is the image data priority; the source address is the address number of the image data sender; the destination address is the address number of the image data receiver; the function number is used to judge the content of the transmitted data and extract the information in the data frame as required; pixel The dot row coordinate X is the X coordinate number of a row of data sent; the control field is related to the number of effective data bits in the data field, and is filled according to the CAN bus international standard ISO11898.

Preferably, the image data sender described in step 1 first divides the image data block transmitted on the CAN bus into several rows according to the image height according to the size of the image data object, and then performs dynamic secondary segmentation processing based on each row , and then divide the image size information and pixel color information to be transmitted into a multi-frame form of several data frames according to a specific frame format.

Preferably, the image data sender described in step 2 sends the size information frame to the image data receiver, and the image data sender sends a data frame containing at least the size information of the image data, and the maximum transmission height is 65536, width It is an image of 65536; its size is also related to the size of the storage area of the slave device and the number of digits of the identifier pixel row coordinates.

As a preference, in the response data frame described in step 3, the first byte of the data field is the sending status flag bit, and the second and third bytes are the row coordinates of the error pixel point, which are not involved here and are defined as 0 , the fourth byte SUM is the check digit of valid data bits.

Preferably, checking the sequence and content of all data frames described in step 5 includes sequence matching, consistency verification, and error handling.

Preferably, the image data sender and image data receiver are system management computer or DSP, when DSP is used as the image data sender, it is required that the master device should send a command message to request the DSP to send image data.

Based on the CAN extended frame format, the present invention discloses a reliable image data transmission method based on dynamic secondary segmentation, sequence matching, consistency check, error handling and other measures for the image data blocks transmitted on the CAN bus. , so as to improve the reliability of transmission and ensure the integrity of data. This method can transmit image data with a maximum height of 65536 pixels and a width of 65536 pixels, which provides powerful help for expanding the application of the CAN bus.

the

Description of drawings

Fig. 1: is flow chart of the present invention.

the

Detailed ways

In order to facilitate those of ordinary skill in the art to understand and implement the present invention, the present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the implementation examples described here are only used to illustrate and explain the present invention, and are not intended to limit this invention.

The bottom layer of the CAN bus communication of the present invention adopts the CAN2.0B protocol specification, the application layer protocol selects CANOpen, and the frame format is an extended frame format.

Please see Fig. 1, the technical scheme that the present invention adopts is: a kind of image data reliable transmission method based on CAN bus, is applied in the system of one main multi-slave, and there is only one master device, which is a system management computer, and the number of slave devices is determined by The actual need determines that the image data transmission is carried out between the master device and the slave device, and there is no mutual transmission between the slave devices; the following steps are included:

Step 1: The image data sender first performs dynamic secondary segmentation processing based on row data on the image data block transmitted on the CAN bus according to the size of the image data object, that is, first divides the image data into several data blocks according to the number of rows, Then, according to a specific frame format, the pixel color information in each data block is divided into a multi-frame form of several data frames.

The format of each frame of data transmitted by the CAN bus includes an arbitration field, a control field and a data field. In order to carry more necessary information without occupying valid data bits, the identifier format in the arbitration field adopts the extended frame identifier format, which at least includes priority control bits, pixel row coordinates, source address, destination address, and function number . In the bit definition example of the identifier given in Table 1, according to the frame priority, the identifier with the lowest binary number has the highest priority, so ID28 and ID27 are defined as priority marks, and 00 is the size information Frame priority, other image data priority is 01. ID26-ID23 is the 4-digit source address identifier of the data sender, especially when the source address is 0000, it means sending from the master device, ID22-ID19 is the 4-digit data receiver target address identifier, which is used to judge whether to receive information and process it The basis, especially when the target address is 0000, it is broadcast transmission, ID18-ID15 is 3 bits is the function identification, and it is also the basis for the receiver to judge the data type of the frame, and the remaining 16 bits are the x coordinates.

Table 1 bit definition example of identifier

ID28-ID27 ID26-ID23 ID22-ID19 priority source address target address ID18-ID16 ID15-ID0 the function number x-coordinate the

The computer acts as the data sender, and the complete format of the image data expansion frame sent to No. 1 slave device with a size of 4X2 is shown in Table 2.

Table 2 Complete format of image data extension frame

As shown in Table 2, the image data with a width of 4 pixels and a height of 2 pixels is divided into 5 frames, the first frame is the size information frame sent first, and the first and second bytes X are 4 image line widths Pixels, the third and fourth bytes Y are 2 pixels in the height of the image column, the fifth byte SUM is the sum check of the data bits, and the remaining four frames are image data information, which are RGB color values, which are stored in the image The first to six bytes of the data field of the data frame, the seventh byte SUM is the sum check of the data bits of this frame. After receiving, the receiver analyzes and restores the data to obtain complete image data and saves it in memory. In particular, when the image width is an odd number, the data receiver only reads the first three data bits in the data field when receiving the last frame of a line of data.

Step 2: The image data sender sends the size information frame to the image data receiver; the size information frame in this embodiment can transmit images with a maximum height of 65536 and a width of 65536, and its size is also the same as the size of the storage area of the slave device, The number of bits in the identifier pixel row coordinates is related.

Step 3: After the image data receiver receives the size information frame, it returns the sending status information to the image data sender, that is, the response data frame, and judges:

After receiving the size information frame, the data receiver returns the sending status information to the data sender, that is, a response data frame. The format of the response data frame after correct reception is shown in Table 3, and the format of the response data frame after incorrect reception is shown in Table 4.

The first byte of the data field is the sending status flag, the second and third bytes are the row coordinates of the error pixel point, which is not involved here, and is defined as 0, and the fourth byte SUM is the data bit of this frame and checksum. If the return information received by the data sender is successful, the data sender will send the first line of image data; if the return information received by the data sender is failure, the size information frame will be automatically resent; if the data sender waits for 1s If the return information is not received, the size information frame will be automatically resent; if it is resent three times, it will be judged as a failure, stop sending, the software will reset the CAN bus by itself, and make the CAN bus continue the previous steps.

Table 3 Response data frame format after correct reception

Control Domain, Identifier data field 11B, 0000B, 0001B, 001B, 0000000000000000B 0xfe, 0x00, 0x00, 0xfe

Table 4 Response data frame format after error reception

Control Domain, Identifier data field 11B, 0000B, 0001B, 001B, 0000000000000000B 0xff, 0x00, 0x00, 0xff

Step 4: The image data sender sends one line of data to the image data receiver in sequence;

Step 5: After receiving a row of data, the image data receiver checks the sequence and content of all data frames (including sequence matching, consistency verification, and error handling), and returns the sending status information to the image data sender according to the inspection results and sends it immediately Status frame, and judge:

If the return information received by the image data sender is successful, then perform the following step 6 in sequence;

If the return message received by the sender of the image data is failure, resend the image data of the row after the frame number according to the returned error coordinate number;

If the sender of the image data waits for 1 second and does not receive the return information, it will turn around and execute the above step 4, and automatically resend the data frame of the line; if it has not received the return information after resending three times, it will be judged as a failure and stop sending , self-reset the CAN bus, and make the CAN bus continue to resend the row of data frames;

After receiving a row of data, the data receiver checks the content and sequence of all data frames, returns a frame sending status information to the data sender according to the inspection result, that is, a row sending status frame, and defines the function number of the row sending status frame as 010 . If the return information received by the data sender is successful, continue to send the next line of data frame; if the return information received by the data sender is failure, then resend the data frame and the data frame of this line according to the returned error coordinate number For the subsequent data, if the data sender waits for 1 second without receiving the return information, it will return to the previous step and automatically resend the data frame of the line. If it has not received the return information after resending three times, it will be judged as a failure and stop sending. The software self-resets the CAN bus and makes the CAN bus continue the steps just now.

According to the inspection results, all the transmissions are correct, and the line sending status frame shown in Table 5 is returned; the data frame with the row coordinate of the sending pixel point of 3 has an error, and the line sending status frame shown in Table 6 is returned, according to the returned error coordinates No., resend the data frame and subsequent data of the line where it is located, that is, the third frame of Table 1. ``

Table 5 All correctly returned rows send status frame

Control Domain, Identifier data field 11B, 0000B, 0001B, 010B, 0000000000000000B 0xfe, 0x00, 0x00, 0xfe

Table 6 The line sending status frame returned by error in the data frame

Control Domain, Identifier data field 11B, 0000B, 0001B, 010B, 0000000000000000B 0xff, 0x00, 0x03, 0xff

Step 6: Send subsequent lines of image data sequentially according to the method described in step 5, until the number of lines of image data correctly received is equal to the number of lines in the size information frame, and the transmission of image data is completed.

The image data sender continues to send the remaining rows of image data, see frames 4 and 5 in Table 1, and the data receiver returns a frame of sending status information, that is, a row sending status frame, to the data sender according to the inspection results.

When the number of correctly received image data lines is equal to the number of lines in the size information frame, the image data transmission is complete.

The image data sender and image data receiver of the present invention are system management computer or DSP, when DSP is used as the image data sender, it is necessary for the master device to send a command message, requiring the DSP to send image data.

Priority description: If the priority of other frames is lower than that of image data, according to the priority of data frames, image data is accepted first, and then other data frames are accepted.

It should be understood that the parts not described in detail in this specification belong to the prior art.

It should be understood that the above-mentioned descriptions for the preferred embodiments are relatively detailed, and should not therefore be considered as limiting the scope of the patent protection of the present invention. Within the scope of protection, replacements or modifications can also be made, all of which fall within the protection scope of the present invention, and the scope of protection of the present invention should be based on the appended claims.

Claims (7)

1. A reliable image data transmission method based on CAN bus, which is applied to a system with one master and multiple slaves. There is only one master device, which is the system management computer, and the number of slave devices is determined by actual needs. The image data is transmitted between the master device and the slave It is carried out between devices, and there is no mutual transmission between slave devices; it is characterized in that it includes the following steps: Step 1: The image data sender first performs dynamic secondary segmentation processing based on row data on the image data block transmitted on the CAN bus according to the size of the image data object, that is, first divides the image data into several data blocks according to the number of rows, Then divide the pixel color information in each data block into a multi-frame form of several data frames according to a specific frame format; Step 2: The image data sender sends the size information frame to the image data receiver; Step 3: After the image data receiver receives the size information frame, it returns the sending status information to the image data sender, that is, the response data frame, and judges: If the return information received by the image data sender is successful, the following steps 4 are performed in sequence; If the return information received by the image data sender is failure, then go back to step 2; If the sender of the image data waits for 1s and does not receive the return information, then go back to step 2; Step 4: The image data sender sends one line of data to the image data receiver in sequence; Step 5: After receiving a row of data, the image data receiver checks the order and content of all data frames, returns the sending status information to the image data sender according to the inspection results, and sends the status frame immediately, and judges: If the return information received by the image data sender is successful, then perform the following step 6 in sequence; If the return message received by the sender of the image data is failure, resend the image data of the row after the frame number according to the returned error coordinate number; If the sender of the image data waits for 1 second and does not receive the return information, it will turn around and execute the above step 4, and automatically resend the data frame of the line; if it has not received the return information after resending three times, it will be judged as a failure and stop sending , self-reset the CAN bus, and make the CAN bus continue to resend the row of data frames; Step 6: Send subsequent lines of image data sequentially according to the method described in step 5, until the number of correctly received image data lines is equal to the number of lines in the size information frame, and the image data transmission is completed. 2. the image data reliable transmission method based on CAN bus according to claim 1, is characterized in that: the specific frame format described in step 1 comprises arbitration field, control field and data field; The identifier in the arbitration field is an extended 29-bit identifier, including priority control bits, source address, destination address, function number and pixel row coordinate X; according to the frame priority, it has the lowest binary The identifier of the number has the highest priority, so ID28 and ID27 are defined as priority control bits, 00 is the priority of the size information frame, and 01 is the priority of image data; the source address is the address number of the image data sender; the destination address is The address number of the image data receiver; the function number is used to judge the content of the transmitted data and extract the information in the data frame as required; the pixel row coordinate X is the X coordinate number of a row of data sent; The control field is related to the number of effective data bits in the data field, and is filled in accordance with CAN bus international standard ISO11898. 3. the image data reliable transmission method based on CAN bus according to claim 1, is characterized in that: the image data sender described in step 1 first according to the size of image data object, to the image data block transmitted on the CAN bus First divide the image into several rows according to the height of the image, and then perform dynamic secondary segmentation processing based on each row, and then divide the image size information and pixel color information to be transmitted into a multi-frame form of several data frames according to a specific frame format. 4. The image data reliable transmission method based on CAN bus according to claim 1, characterized in that: the image data sender described in step 2 sends the size information frame to the image data receiver, and its image data sender sends A data frame that contains at least the size information of the image data, and can transmit images with a maximum height of 65536 and a width of 65536. 5. the image data reliable transmission method based on CAN bus according to claim 1, it is characterized in that: the response data frame described in the step 3, its data field first byte is the sending status flag bit, the second, The three bytes are the row coordinates of the error pixel point, and the fourth byte SUM is the check digit of the valid data bit. 6. The image data reliable transmission method based on CAN bus according to claim 1, characterized in that: the order and content of checking all data frames described in step 5 includes order matching, consistency verification, and error handling. 7. the image data reliable transmission method based on CAN bus according to claim 1, is characterized in that: described image data sender and image data receiver are system management computer or DSP, when DSP is as image data sender , the master device should send a command message, requiring the DSP to send image data.