SERIAL DATA COMMUNICATION WITH IN-FRAME RESPONSE

Abstract

A method for a slave bus and a master bus includes receiving a first frame via a first data channel, wherein the first frame includes at least first header data, first payload data and first checksum. The method further includes implementing a function depending on the header data contained in the received first frame, and generating a second frame including second header data, second payload data, which are determined by the implemented function, and a second checksum. The second checksum is ascertained at least on the basis of the second payload data and the first header data contained in the received first frame. The method also includes transmitting the second frame via a second data channel simultaneously with receiving the first frame via the first data channel.

Claims

1. A method comprising: receiving a first frame via a first data channel, wherein the first frame comprises at least first header data, first payload data and a first checksum; and implementing a function depending on the header data contained in the received first frame; generating a second frame comprising second header data, second payload data, which are determined by the implemented function, and also a second checksum, which is ascertained at least on a basis of the second payload data and the first header data contained in a currently received first frame; and transmitting the second frame via a second data channel simultaneously with receiving the first frame via the first data channel.

2. The method as claimed in claim 1, wherein the second frame is transmitted in the same time interval in which the first frame is received.

3. The method as claimed in claim 1, in the first frame and the second frame are received and respectively transmitted synchronously with a clock signal.

4. The method as claimed in claim 1, wherein the first header data contain an address of a memory element, and the function is applied to that part of the memory which is designated by the address.

5. The method as claimed in claim 1, wherein the first header data include an address of a memory, and the function comprises reading data from a memory element designated by the address, and wherein the second payload data are dependent on the data read.

6. The method as claimed in claim 1, wherein the first header data contain an address of a memory, and the function comprises writing data to a memory element designated by the address, and wherein the data written are the first payload data or dependent thereon.

7. The method as claimed in claim 6, wherein before writing the data, the data stored in a part of the memory which is designated by the address are read, and wherein the second payload data are the data read or are dependent thereon.

8. The method as claimed in claim 1, wherein the second payload data identify a transmitter of the second frame and/or comprise status information.

9. The method as claimed in claim 1, further comprising: validating the first checksum on a basis of received first header data and received first payload data.

10. The method as claimed in claim 1, wherein the second checksum contained in the second frame is ascertained on the basis of the second header data, the second payload data and on the basis of the first header data contained in the received first frame.

11. The method as claimed in claim 1, wherein the second header data are dependent on the first header data.

12. A bus node comprising: a transmitting and receiving device configured to receive a first frame via a first data channel, wherein the first frame comprises at least first header data, first payload data and a first checksum; a control logic configured to implement a function depending on the first header data contained in a currently received first frame; and a frame encoder configured to generate a second frame which comprises second header data, second payload data, which are determined by the implemented function, and also a second checksum, wherein the frame encoder is further configured to ascertain the second checksum on a basis of the second payload data and further on the basis of the first header data contained in the received first frame; and wherein the transmitting and receiving device is further configured to transmit the second frame via a second data channel simultaneously with receiving the first frame via the first data channel.

13. A method comprising: generating a first frame comprising at least first header data, first payload data and a first checksum; transmitting the first frame via a first data channel, and simultaneously with transmitting the first frame: receiving a second frame comprising second header data, second payload data and also a second checksum; and validating the second checksum on a basis of the second payload data and further on the basis of the first header data contained in a generated first frame.

14. The method as claimed in claim 13, wherein the second checksum is validated on the basis of the second header data, the second payload data and further on the basis of the first header data generated for the generated first frame.

15. A bus node comprising: at least one processor and a memory containing instructions which, when they are executed on the processor, cause the bus node to carry out the method as claimed in claim 13.

16. A non-volatile memory medium having software instructions which, when they are executed on a processor of a bus node, cause the bus node to carry out the method as claimed in claim 13.

17. A bus node comprising: a transmitting and receiving device configured to transmit a first frame via a first data channel, wherein the first frame comprises at least first header data, first payload data and a first checksum, and configured to receive via a second data channel a second frame comprising second payload data and also a second checksum; a frame decoder configured to check the second checksum on a basis of the second payload data and further on the basis of the first header data contained in the first frame; and wherein the transmitting and receiving device is further configured to receive the second frame via a second data channel simultaneously with transmitting the first frame via the first data channel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Exemplary embodiments are explained in greater detail below with reference to figures. The illustrations are not necessarily true to scale and the exemplary embodiments are not restricted only to the aspects illustrated. Rather, importance is attached to representing the principles underlying the exemplary embodiments. In respect of the figures:

[0011] FIG. 1 illustrates one example of a system with two bus nodes connected via an SPI bus;

[0012] FIG. 2 schematically illustrates frame-based full-duplex bus communication via a serial bus;

[0013] FIG. 3 schematically illustrates the concept of the in-frame response (IFR) in frame-based serial bus communication;

[0014] FIG. 4 illustrates one example of a method—implemented in a slave bus node—for safeguarding the response frames by means of checksums with the use of in-frame responses;

[0015] FIG. 5 illustrates one example of a method—implemented in a master bus node—for checking the checksum contained in a response frame with the use of in-frame responses;

[0016] FIG. 6 is a flow diagram for exemplary illustration of a method for a slave bus node; and

[0017] FIG. 7 is a flow diagram for exemplary illustration of a method for a master bus node.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0018] FIG. 1 illustrates one example of a system with two bus nodes connected via an SPI bus. However, the exemplary embodiments described here are not restricted to an SPI bus, rather the concepts described below can also be applied to any other serial bus systems such as e.g., HSSL (High Speed Serial Link), MSB (Microsecond Bus), I2C-Bus (Inter-Integrated Circuit Bus) or the like.

[0019] The bus node 10 shown in FIG. 1 is referred to hereinafter as controller or as master bus node, which controls the bus communication. The bus node 10 can be for example a microcontroller having an SPI interface ii and at least one processor 12 configured to execute software instructions contained in a memory in order to implement the concepts, functions and method steps described here. Programmable microcontrollers having SPI interface are known per se and are therefore not described in greater detail here. It goes without saying, however, that the bus node 10 need not necessarily have a processor for executing software instructions. In addition or instead, it is also possible to use a hardwired or one-time programmable (OTP) logic.

[0020] The SPI interface ii of the bus node 10 is connected to a corresponding SPI interface 21 of a further bus node 20 via a plurality of bus lines, which in the case of an SPI bus are usually designated by CSN (Chip Select), SCK (Serial Clock), MOSI (Master Out Slave In) and MISO (Master In Slave Out). The signals transferred via the respective bus lines are likewise designated by CSN, SCK, MOSI and MISO. The master bus node stipulates the points in time at which frames are transmitted (activation of CSN) and also the data transfer rate (generation of SCK). Moreover, the master bus node also defines whether data are read or written (as viewed from the master bus node in each case).

[0021] In some applications, the signal CSN can be regarded as optional and is used in particular if a plurality of slave bus nodes are connected to a master bus node. In other applications, CSN is indispensable; by way of example, CSN may be incorporated in a safety concept of a component. SCK denotes a shift clock signal, which is output by the master bus node 10 for the synchronization of the data transfer on the data channels MISO and MOSI. The data channel MOSI (having at least one data line) serves for data transfer from the master bus node 10 to the slave bus node 20, and the data channel MISO (having likewise at least one bus line) serves for data transfer in the other direction. In the case of a full-duplex data transfer, data are transferred on both data channels, MOSI and MISO, simultaneously and synchronously with the shift clock signal SCK.

[0022] The serial data transfer is usually effected on the basis of frames (MOSI frames from the bus node 10 to the bus node 20; MISO frames from the bus node 20 to the bus node 10). The structure of a frame will be explained in even greater detail later. In the bus node the data D.sub.IN received by the SPI interface 21 are forwarded to a frame decoder/encoder 22. In the other direction, the frame decoder/encoder 22 supplies the data D.sub.OUT to be transferred to the SPI interface. The frame decoder/encoder 22 is configured firstly to “unpack” and validate the data contained in a MISO frame and to “pack” and safeguard the raw data to be transmitted in a MISO frame.

[0023] Validating and safeguarding data contained in a frame usually comprises calculating or verifying a checksum. In the exemplary embodiments described here, the cyclic redundancy check (CRC) is used for calculating and verifying checksums, although other algorithms for ascertaining and verifying checksums are also possible. In the simplest case, the checksum consists of one or more parity bits. Various CRC methods or CRC polynomials and other methods for ascertaining and verifying checksums are known per se and are therefore not explained in detail here. In general, the frame decoder/encoder 22 adds a checksum to those (raw) data D.sub.READ which are packed into a frame (to be transmitted), and verifies the checksum contained in a (received) frame in order to check the integrity of the received data (e.g., an address ADDR, D.sub.WRITE)

[0024] In the case of a write access, bus node 10 writes data D.sub.WRITE to address ADDR in the bus node 20. For this purpose, D.sub.WRITE and ADDR have to be transferred in one or more MOSI frames. In the case of a read access, bus node 10 reads data D.sub.READ from an address ADDR of bus node 20. For this purpose, it is necessary to transfer the address ADDR in at least one MOSI frame and the read data D.sub.READ in at least one MISO frame. The address ADDR identifies a location in the modules or memory areas of the bus node 20 at which data can be written or read.

[0025] In the present example, the data received in a MOSI frame in the (slave) bus node 20 are designated by D.sub.WRITE and ADDR and are fed to a control logic 23. The data transmitted in a MISO frame by the bus node 20 are output by the control logic 23 to the frame decoder/encoder 22 and are designated by D.sub.READ in the present example. The construction of a frame and the meaning of the data contained therein will be explained in even greater detail later (cf. FIG. 3). The control logic 23 can access a memory 26 and also one or more modules X, Y, Z e.g., via an internal data bus 25. A module can be an arbitrary data source or data sink. In one simple example, a module is a simple semiconductor switch that can be switched on or off by means of a specific command or that supplies on request a value for the current flowing via the (closed) switch. A module can also be a sensor that regularly supplies updated measurement values (e.g., a temperature).

[0026] FIG. 2 schematically illustrates frame-based full-duplex data transfer via a serial bus, wherein a sequence of frames is in each case transferred both via the MOSI data channel and via the MISO data channel. In the example illustrated, the frames F1 (i.e., the data contained therein) transferred via the MOSI data channel can be interpreted as commands, for example as write and read commands (e.g., “write A”, “read B”, etc.). The frames F2 transferred via the MISO data channel contain the responses to the respective commands (e.g., the data read out from a register).

[0027] The frames F1 and F2 are transferred synchronously with a clock signal (which is generated by the bus node 10 and output to the SCK line) and simultaneously. In the examples described here, “simultaneously” is understood to mean that the two frames (from and to the master) overlap at least temporally. In one exemplary embodiment, in a specific time interval in which a MOSI frame is transferred, a MISO frame is also transferred simultaneously. Particularly in the case of an SPI, the transfer is isochronous since both frames (apart from avoidable propagation delay effects) begin and end substantially at the same point in time.

[0028] In systems with a next-frame response (NFR) structure, therefore, the response to a command transferred in a MOSI frame is only transferred in a temporally succeeding MISO frame. The MISO frames F2 lag behind the corresponding MOSI frames F1 temporally by at least one frame duration. This time offset is undesired in some applications, however, for which reason a concept known as in-frame response (IFR) was developed. One example of this is illustrated in FIG. 3.

[0029] As illustrated in FIG. 3, each frame (MOSI and MISO frames) comprises at least a first field with header data, a second field with payload data and a third field with a checksum. The slave bus node (e.g., bus node 20) can implement a specific function depending on data contained in a MOSI frame F1. Said function can be dependent e.g., on the header data. By way of example, the header data designates an address (e.g., a register address) for a write or read operation. A portion of the header data (just one bit in a simple case) indicates whether a write or read operation is to be implemented. However, the information concerning the function/operation to be implemented can also be considered as part of the address. In the case of a write operation, the data to be written are in the payload data field of the MOSI frame F1. In the case of a read operation, the payload data of the MOSI frame F1 can also be dummy data (e.g., a sequence of zeros). The checksum in the checksum field of the MOSI frame F1 (MOSI CRC) safeguards the data of the MOSI frame that are contained in the header field and in the payload field. That means for the example illustrated that the CRC checksum (MOSI CRC) is calculated in the master bus node 10 on the basis of the header data and the payload data.

[0030] In the case of an in-frame response, the slave bus node 20 already implements the function (e.g., a read operation) requested by the master bus node as soon as the header data of the MOSI frame F1 have been received. The MOSI CRC has not yet been evaluated at this point in time. The response (e.g., the data D.sub.READ read from a register at the location ADDR), is sent in the payload field of the MISO frame F2 while the corresponding MOSI frame F1 is still being received. The header data of the MISO frame F2 can be dummy data (e.g., a sequence of zeros), on which currently received MOSI header data are dependent, or can be e.g., status information indicating the current status of the bus node 20 (e.g., independently of the currently implemented operation). In one example, the header data (ADDR) currently received in the MOSI frame F1 are copied bit by bit into the header data field of the MISO frame F2 (status information identical to MOSI header data). The checksum in the checksum field of the MISO frame F2 (MISO CRC) protects the payload data of the MISO frame F2 and optionally also the header data of the MISO frame F2. That means for the example illustrated that the CRC checksum (MISO CRC) is calculated in the slave bus node 20 (e.g., in the frame decoder/encoder 22) on the basis of the payload data and optionally also on the basis of the header data of the MISO frame F2.

[0031] It can already be discerned from the temporal sequence illustrated in FIG. 3 that at the point in time at which the slave bus node 20 has received the header data (e.g., the address ADDR for a read operation) of the MOSI frame F1, the requested function (e.g., the read operation) must be implemented immediately even before objectively there is a possibility of verifying the checksum (MOSI CRC) in order to validate the data received by the slave bus node 20. At a point in time at which the frame decoder/encoder 22 in the slave bus node 20—possibly—establishes that the received frame F1 is erroneous, the frame F2 with the response has already been transmitted back to the master bus node 20. In the case where the verification of the checksum (MOSI CRC) fails (e.g., as a result of a transfer error of the read address ADDR), the slave bus node 20 would only notice afterward that the response to an “incorrectly understood question” has been transmitted. However, only with the next MISO frame F2 is the slave bus node 20 able to inform the master bus node 10 about the erroneous checksum, which would at least partly nullify again the advantage of the in-frame response. In the following FIGS. 4 and 5 a novel concept is elucidated which makes it possible that the master bus node 10, already on the basis of that MISO frame which contains the in-frame response, can assess whether the slave bus node 20 has performed the correct function (and has “correctly understood” the question).

[0032] FIG. 4 illustrates the process of verifying the checksum (MOSI CRC) contained in the MOSI frame F1 and also generating/calculating the checksum (MISO CRC) to be transmitted in the MISO frame F2 in a slave bus node 20 (cf. FIG. 1). The frame decoder/encoder 22 contained in the bus node 20 can be functionally divided into two parts, which are designated hereinafter as frame decoder 221 and frame encoder 222. The frame decoder 221 receives the data DIN of a received MOSI frame and extracts therefrom the header data (e.g., address ADDR for write access), payload data (e.g., the data word DWRITE to be written) and checksum (MOSI CRC) contained therein. The frame decoder 221 is further configured to verify the received checksum. If a checksum error is detected, then e.g. a process of writing to an address is not performed, but for example a predetermined value is indicated in an error register. During the verification of the checksum, the latter is calculated on the basis of the header data and the payload data of the received MOSI frame F1 and is compared with the received checksum in the checksum field. In the event of deviations between the calculated checksum and the received checksum, an error is signaled. The complete check and the process of writing with data that are safeguarded (by means of CRC) can only take place after the complete MOSI frame has been received (e.g., after the deactivation of the CSN signal).

[0033] In the present example, before implementing the write operation, the content of the addressed register is read out (data word D.sub.READ) and the data word D.sub.READ read is sent as an in-frame response to the write command back to the bus node 10 (master node). Directly after receiving the destination address ADDR in the MOSI header data field (still before the check of the MOSI CRC), the control logic 23 performs a read operation at the received address ADDR and transfers the data read there to the frame encoder 222. The frame encoder 222 receives the data word D.sub.READ (e.g., from the control logic 23) and also status information and generates therefrom the MISO/response frame F2 to be transmitted, wherein the MISO header data represent the status information and the MISO payload data represent the data word D.sub.READ. The frame encoder 222 is configured to calculate a checksum on the basis of the MOSI header data (address) of the presently received MOSI frame F1, the MISO payload data of the presently current MISO frame F2 and optionally also on the basis of the MISO header data of the presently current MISO frame F2. The calculated checksum value MISO CRC is written into the checksum field of the current MISO frame F2 and transferred via the bus to the master bus node 10. As already mentioned, the received MOSI frame Fl and the response frame F2 (MISO frame) are transferred in parallel in the same time slot. In the case of a SPI interface, the MOSI and MISO frames are transferred in parallel (in a manner controlled by the common signals CSN and SCK). In the case of other transfer interfaces, MOSI and MISO frames can be transferred with a temporal offset relative to one another. As soon as a slave bus node initiates an action in response to an only partly received MOSI frame (still before the check on the complete MOSI frame), it is possible to apply the mechanisms described here for safeguarding the MISO frame.

[0034] In contrast to known concepts, the header data contained in the presently received MOSI frame F1 are taken into account—as illustrated schematically in FIG. 4—in the responding slave bus node 20 during the calculation of the checksum 4 safeguarding the MISO/response frame F2. In this case, the slave bus node uses data for creating the MISO checksum which originate from the current frames from two different transmitters which are transferred at the same time or in an overlapping manner.

[0035] The master bus node 10 receives by way of its SPI interface 11 (see FIG. 1) a MISO/response frame F2 (data D.sub.OUT r transmitted by the slave bus node) and implements the verification of the checksum (MISO CRC) contained in the received MISO/response frame F2, on the basis of the MOSI header data (address) that were used previously for generating the MOSI frame F1 transferred at the same time as the MISO frame F2 or in a manner overlapping the latter, and also on the basis of the MISO payload data of the presently received MISO/response frame F2 and optionally on the basis of the MISO header data of the presently received MISO/response frame F2. This is illustrated in the lower part of FIG. 5. The upper part of FIG. 5 illustrates the safeguarding of a MOSI frame F1 to be transmitted in the master bus node 10, for which the checksum (MOSI CRC) is calculated on the basis of the MOSI header data (address) and the MOSI payload data of the relevant frame in a conventional manner.

[0036] During the verification of the checksum of the received MISO/response frame F2, the master bus node 10 can already recognize whether the slave bus node 20 has correctly received the MOSI header data (which contain e.g., the address for a write or read operation) of the corresponding MOSI frame F1. If that were not the case, the header data (of the MOSI frame F1) received in the slave bus node 20 would not be the same as those used for the generation of the MOSI frame in the master bus node 10 (in this case, the slave bus node 20 would have “incorrectly understood” the master bus node 10). Since the received MOSI header data are taken into account in the checksum calculation in the slave bus node and the intended MOSI header data are taken into account in the checksum verification in the master bus node, during the verification of the checksum of a received MISO/response frame the master bus node can immediately recognize whether the slave bus node 20 has correctly received the header data of the corresponding MOSI frame (and thus the information about the function/operation to be performed).

[0037] One example of the concept described here is summarized below with reference to the flow diagrams in FIGS. 6 and 7. The flow diagram in FIG. 6 illustrates a method for a slave bus node (cf. FIG. 1, bus node 20). Accordingly, the method comprises receiving a first frame (MOSI frame) via a first data channel (MOSI data channel). Said MOSI frame contains at least first header data, first payload data and a first checksum (see FIG. 6, step S1). The method further comprises implementing a function depending on the header data contained in the already received part of the first frame (see FIG. 6, step S2) and generating a second frame (response/MISO frame). The latter contains second header data, second payload data, which are determined by the implemented function (e.g., a read operation), and also a second checksum. Said second checksum is ascertained at least on the basis of the second payload data and the first header data contained in the presently received MOSI frame (see FIG. 6, step S3). Furthermore, the method comprises transmitting the MISO frame via a second data channel simultaneously with receiving the MOST frame via the first data channel (see FIG. 6, step S4).

[0038] The second header data can additionally also concomitantly influence the second checksum in order to completely safeguard the MISO frame by means of the checksum. Since the header data of the presently received MOSI frame also concomitantly influence the checksum calculation, the master bus node (cf. FIG. 1, bus node 10) upon receiving the response/MISO frame, can check whether the slave bus node has correctly received the header data of the MOSI frame.

[0039] The MISO frame is transmitted in the same time interval in which the MOSI frame is received (simultaneously, i.e. in the same time interval or in an overlapping manner). The payload data of the MISO frame can therefore represent an in-frame response to the MOSI frame. In the case of an SPI interface, the MOSI frame and the MISO frame are usually received and respectively transmitted synchronously with a common clock signal. The abovementioned function implemented by the slave bus node can comprise a memory access, wherein the header data of the MOSI frame contain the address of a memory element which is accessed during the implementation of the function in the slave bus node. The function can be in particular a read or write operation. In the case of a read operation, the payload data in the response frame (MISO frame) can be the data read or can be dependent thereon. In the case of a write operation, the payload data in the received MOSI frame are the data to be written to the memory or the data to be written to the memory are dependent on the payload data of the received MOSI frame. Before the write access, the content (overwritten later) of the memory can be read and can be sent back as an in-frame response to the master bus node. Alternatively, the payload data of the response frame can also identify the transmitting (slave) bus node or include status information. The status information transmitted back can also contain the previously received address.

[0040] When the MOSI frame has been completely received by the slave bus node, the first checksum contained in the MOSI frame can be validated on the basis of the received first header data and the received first payload data. At this point in time, the function initiated by the MOSI frame has already been performed and the corresponding data as an in-frame response have already been completely transferred back to the master bus node, or their transfer has begun.

[0041] The flow diagram in FIG. 7 illustrates a corresponding method for a master bus node. The method accordingly comprises generating a first frame (MOSI frame) comprising at least first header data, first payload data and a first checksum (see FIG. 7, step M1). The method further comprises transmitting the MOSI frame via a first data channel (see FIG. 7, step M2) and13 simultaneously with (in parallel with), or with a slight time offset with respect to, transmitting the MOSI frame—receiving a second frame (MISO frame) comprising second header data, second payload data and also a second checksum (see FIG. 8, step M3). Furthermore, the method comprises validating the second checksum in the master bus node on the basis of the second payload data and further on the basis of the first header data contained in the previously generated MOSI frame (data intended for transfer). In one exemplary embodiment, during the validation of the second checksum, the second header data can also be taken into account (provided that they are also taken into account in the slave bus node).

[0042] While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.