Digital message transmission protocol

The present invention relates to microprocessors test. It relates more particularly to a method and a digital data transmission device between a monitoring circuit integrated in a chip of the microprocessor and an analysis tool.

1 shows schematically an integrated circuit 10 comprising a microprocessor (<i>μ</i>P) 12, a memory (MEM) 14 and input / output (I / O) 16. The microprocessor 12 is intended to execute a stored program or software in memory 14. Under control of the program, microprocessor 12 can process data from the input / output terminals 16 or stored in memory 14 and read or write data from input / output 16.

In order to check the operation of the microprocessor is generally incorporates the integrated circuit 1 October 18 monitoring circuit (TEST). The monitoring circuit 18 is adapted to read the specific data from the microprocessor 12 during the course of a program, and may perform processing on the read data. test terminals 22 connect the monitoring circuit 18 to an analytical tool 24. The scanning tool 24 may process the received signals, for example according to commands provided by a user, and provide a detailed analysis the operation of the microprocessor 12. In particular, the analysis tool 24 may determine the sequence of instructions of actually executed by the microprocessor 12 program.

The number of test terminals 22 may be of the same order of magnitude as the number of input / output terminals 16, for example 200 to 400 terminals. The test terminals 22 and the connections of the monitoring circuit 18 occupy a significant silicon surface, which causes an unwanted increase in the cost of the circuit. For this, a first version of the integrated circuit 10 including the monitoring circuit 18 and the test terminals 22 is produced in small quantities to make the development of the microprocessor program 12 or "user program." After this development, a version of integrated circuit 10 rid of the monitoring circuit 18 and the test terminals 22 is sold. This involves the construction of two versions of the integrated circuit, which requires significant work and is relatively expensive. In addition, the final chip is not necessarily identical to the test chip.

To overcome the drawbacks mentioned above, we try to achieve a monitoring circuit 18 which occupies a small area and requires only a small number of test terminals 22, which reduces the cost of the monitoring circuit. The monitoring circuit 18 can then be left on the finally sold integrated circuit 10.

It is therefore sought to reduce the number of signals provided by the monitoring circuit 18. To do this, are directly performed at the monitoring circuit 18 some logical operations on the data measured in the microprocessor 12 so as to transmit only messages having an important information content.

Thus, the IEEE-ISTO-5001 standard in preparation proposed in its 1999 version, available for example on the site www.ieee-isto.org/Nexus5001, a particular protocol message exchange between a monitoring circuit and a tool analysis for a monitoring circuit 18 requiring only a reduced number of test terminals 22.

The monitoring circuit is provided to monitor the operation of the microprocessor to provide test terminals predetermined messages only when certain predetermined instructions are executed. Messages can indicate how many instructions have been executed since the previous message. Messages may also be provided to indicate that certain predetermined points of the program are achieved. The analysis is intended to restore the functioning of the microprocessor tool, that is to say, the program sequence in the microprocessor from the received and the program code messages. The list of message types and structure are described in Section 6 of the IEEE-ISTO-5001. Each message is divided into packets of variable size and comprises at least one packet. In each packet, bits are ordered from left to right by increasing weight. IEEE-ISTO-5001 standard provides a message can include packet size specified in the standard or variable (set by the user). For simplicity, we consider later a variable-sized packet may include one or more unrepresented fixed size packets.

To limit the number of test terminals, each packet is divided into segments of n bits, where n is for example between 4 and 16, transmitted through a MDO bus n bits. The n bits of the lower weight of the first message data packet are copied bit by bit in a first segment, then the n bits of the lower left of the data packet weight are copied bit by bit in a second segment, and so on until every bit package was copied. The bits of the highest unused weight of the final segment thus formed receive a predetermined value, for example 0. Each data packet is divided into segments in the foregoing manner. The segments are transmitted after the bus MDO, in step with a clock signal not shown to own monitoring circuit. To allow the reconstruction of the data packets from the segments, it is expected to pass with each segment on additional test terminals MSEO a code that enables the analysis tool to identify the nature of the data in the segment . IEEE-ISTO-5001 standard provides MSEO codes to identify a segment contains: a message start (SM segment), intermediate data (NT segment), a packet end (EP segment), an end of message ( EM segment), or that this segment is an empty segment (segment ID) corresponding to a period of inactivity between two messages.

Instead of directly identifying each segment by a particular code, which would require at least three bits, the IEEE-ISTO-5001 standard provides for giving the code MSEO a value that, if one knows the type of the previous segment, allows determine the type of the transmitted segment. MSEO the code identifies the transition from the previous segment and the transmitted segment.

Figure 2 illustrates schematically all possible sequences of segments provided by standard IEEE-ISTO-5001. The circles bearing references SM, NT, EP, EM and ID each represent a type of transmitted segment. The arrows joining two circles indicate that the two corresponding segments can be transmitted one after another. An arrow from a circle to come back indicates that this segment can be transmitted several times in a row. For example, a segment SM can follow a segment SM. This indicates that the message sent was very short and included one package of less than or equal to a segment. In other words, the first segment SM contained both the beginning and end of a message. A segment SM can be transmitted after a segment SM, EM or ID, and ID segment can be transmitted after a segment EM or ID. Similarly, an NT or EM segment may be transmitted after a segment SM, NT or EP. Finally, a segment EP can be transmitted after a segment SM, NT, or EP.

Figure 2 also shows the value taken by the MSEO code depending on the type of the transmitted segment and type of the previous segment. MSEO value of the code associated to each transmitted segment is the value associated with the arrow from the previous segment to the transmitted segment. A segment SM is identified by a code MSEO value 00 if the previous segment was a MS or segment ID, and is identified by a value 10 if the previous segment was a segment SM. NT segment is identified by a value of 00 MSEO code regardless of the previous segment. An EP segment is identified by a value 01 of MSEO code regardless of the previous segment. MS or ID segment type is identified by a value 11 of code MSEO whatever the previous segment.

Upon receipt of the segments, the analysis tool reconstitutes the packets of each message by putting end to end the segments containing data of the same packet.

3A shows by way of example the transmission of a message 30 comprising three packs 31, 32 and 33 respectively having 9, 20 and 11 bits. Figure 3A also illustrates the MSEO code that is transmitted with each segment of the message 30. In the message 30 by an MDO bus n = 8 bits, the first packet 31 is divided into a first segment 311 of message start (MSEO = 00 assuming that the previous segment was a segment ID) containing 8 bits of the lower weight of the package 31 and a second segment 312 packet end (MSEO = 01) containing the most significant bit package 31, followed by seven zeros. Similarly, the package 32 is divided into three segments 321 (type NT, MSEO = 00), 322 (type NT, MSEO = 00) and 323 (type EP, MSBO = 01) respectively containing the 8-bit the lower weight, the 8 bits following the lowest weight and the 4 bits of the most significant package of 32, followed by 4 zeros. The package 33 is divided into two segments, 331 (type NT, MSEO = 00) and 332 (type EM, MSEO = 11) respectively containing the 8 bits of the least significant, and 3 bits of the most significant the packet 33 followed by 5 zeros.

An object of the present invention is to optimize the process of transmission of messages described above to reduce the number of segments transmitted in various particular cases.

Another object of the invention is to provide a device for implementing such a method.

To achieve these objects, the present invention provides a method for transmitting, between a monitoring circuit integrated to a microprocessor and an analysis tool, digital messages each comprising at least one data packet, comprising the steps of:<ul><li>a / dividing each data packet into successive segments of same predetermined size, each segment being classified according to one or other of the five following types of segment:<ul><li>segment containing a message start;</li><li>segment containing intermediary data;</li><li>segment containing a packet end;</li><li>segment containing a message end; or</li><li>empty segment;</li></ul></li><li>b / send along each segment an identification signal characterizing the type difference between the segment and the previous segment; and</li><li>c / reconstituting the packets of each message by putting end to end the segments containing the same packet data; wherein a segment containing both the start and end of a message is classified as being a segment containing a message end, and a segment containing both the start of a message and the end of a first packet the message is classified as being a segment containing a packet end.</li></ul>

According to one embodiment of the invention, a segment containing a message start or an empty segment may be transmitted after a segment containing a message end or an empty segment; a segment containing intermediary data can be transmitted after a segment containing a message start or intermediary data or a packet end; and a segment containing a packet end or an end of message can be transmitted after any type of segment.

According to one embodiment of the invention, the identification signal:<ul><li>a first value if the transmitted segment contains a message start or intermediate data;</li><li>a second value if the transmitted segment contains a packet end;</li><li>a third value if the transmitted segment contains a message end and if the previous segment contained a message end or was an empty segment; and</li><li>a fourth value if the transmitted segment is empty, or if the transmitted segment contains a message end and if the previous segment contained a message start, intermediate or end data packet.</li></ul>

The present invention also relates to a transmission device, between a monitoring circuit integrated to a microprocessor and an analysis tool, digital messages each comprising at least one data packet, comprising:<ul><li>means for dividing each data packet into successive segments of same predetermined size, each segment being classified according to one or other of the five following types of segment:<ul><li>segment containing a message start;</li><li>segment containing intermediary data;</li><li>segment containing a packet end; </li><li>segment containing a message end; or</li><li>empty segment;</li></ul></li><li>means for sending along each segment an identification signal characterizing the type difference between the segment and the previous segment; and</li><li>a way to replenish the packets of each message by putting end to end the segments containing the same packet data;</li></ul>wherein the means for dividing each data packet class a segment containing both the start and end of a message as being a segment containing a message end, and classifies a segment containing both the start of a message and the end of a first packet of the message as being a segment containing a packet end.

These objects, features and advantages, and others of the present invention will be discussed in detail in the following description of specific embodiments in non-limiting in connection with the accompanying drawings:<ul><li>Figure 1, previously described, schematically shows an integrated circuit provided with a monitoring device;</li><li>Figure 2, previously described, illustrates a protocol for transmitting messages as defined in the 1999 version of the IEEE-ISTO-5001 standard;</li><li>3A and 3B illustrate an example of transmitting a message according to the protocol of Figure 2 for two different bus sizes MDO;</li><li>4 illustrates a messaging protocol according to the present invention; and</li><li>5 illustrates the transmission of the message of Figure 3B according to the protocol of figure 4.</li></ul>

The inventor has analyzed the operation of the messaging system described above in the case where the MDO bus has a data width of n equal to or greater than the size of the first, and possibly unique, data packet of each message.

3B illustrates the transmission of the message 30 of Figure 3A and segments used to transmit such a message by an MDO bus of n = 16 bits. One segment 311 'contains 9 bits of the first packet 31 followed by seven zeros, and this segment is associated with a start of message code (MSEO = 00). As the protocol does not provide the opportunity to indicate that the end of the first packet was sent to the same segment, it must transmit a next segment 312 'package associated with an end MSEO code = 01, which only contains zeros before transmitting the next packet segments. The next packet, 32, is then split into a segment 321 'type NT (MSEO = 00) and a segment 322' type EP (MSEO = 01) respectively containing 16 bits of the least significant, and 4 bits of the most significant of the packet 32 ​​followed by 12 zeros. The package 33 is transmitted in one segment 331 'end of message (MSEO = 11) containing its 11 bits followed by 5 zeros.

Generally, when the first packet of a message having a plurality of packets is less than or equal in size to the size n of the MDO bus, it must first packet according to the preceding protocol, be transmitted into two segments. The transmission of the second segment, which contains no data, uselessly monopolizes the test terminals and reduces the bandwidth of the bus MDO.

The present invention aims a segment in message transmission process in which a segment containing both the start of a message and the end of a first, and possibly unique, the message packet can be immediately followed by a segment containing data, for example the beginning of a second message packet or the beginning of a new message.

4 illustrates a segment in message transmission protocol according to the present invention. Figure 4 lists the references used to identify the different segments in Figure 2. Figure 4 shows in relation to FIG 2 the differences that will now be described in relation to the arrows drawn in dashed lines.

According to the present invention, a segment is classified as Type EP not only if it only contains a packet end, but also if it contains both the start of a message more packets and the end of the first packet the message. This last case arises if the first packet of a message is shorter than a segment. Such a segment EP message start and end packet may follow an empty segment ID when such a message start is transmitted after a period of inactivity (dotted arrow 41 fat) or a segment EM when such early message is transmitted after a previous message (bold dotted arrow 42).

According to the present invention, a segment is classified as Type EM not only if it contains only an end of message, but also if it contains both the start and end of a message. The latter case is when a message is shorter than a segment. Such EM segment start and end of message ID may follow a segment when a short message is transmitted after a period of inactivity (dotted arrow 43 fat) or a segment EM when a short message is sent immediately after a previous message (bold dotted arrow 44).

The possibility of classifying a segment as type EM if it contains both the start and end of a message replaces the possibility provided by the protocol of Figure 2, to classify such a segment as being of type SM . Thus, according to the present invention (as indicated by the arrow in light dashed lines), a segment SM can no longer follow a segment SM (and thereby indicate that the first segment SM contains a shorter message that segment).

In Figure 4, an EP segment is identified by a value 01 of MSEO code regardless of the previous segment. EM segment is identified either by a value 11 of MSEO code if the previous segment was a SM, NT or EP segment, or by a value 10 of the code MSEO if the previous segment was an EM or segment ID. SM segments, NT and ID are identified in the same way that was described previously.

The present invention can be implemented in a device as shown in Figure 1 by the skilled person having read the section 8 of the 1999 version of the standard IEEE-ISTO-5001. For this, the monitoring circuit 18 and the scan tool 24 will be programmed according to the protocol of Figure 4.

5 illustrates the transmission of the same message 30 as illustrated in Figure 3B by the MDO bus of n = 16 bits according to the protocol of FIG 4. One segment 311 "type EP contains 9 bits of the first packet 31 followed 7 zeros. This segment 311 "is followed by the same segments 321 ', 322' and 331 'as described in connection with Figure 3B. With the segment 311 "is transmitted a MSEO code having the value 01, and with segments 321 ', 322' and 331 'are transmitted as previously MSEO of codes having the values ​​00, 01 and 11.

The present invention allows in the example illustrated in Figure 5 into four segments to transmit a message, in the same conditions, was to be transmitted into five segments according to the protocol of Figure 2.

In the case of messages comprising two packets each having a size less than or equal to a segment, the present invention allows to send only two segments instead of three.

The present invention also allows in particular to transmit in only two segments (EM segment and an EP segment) succession of a message of length less than a first segment and a packet length less than a segment of a message following. Such sequence would have been transmitted in four segments (a segment SM monitoring segments EM, SM and PE) according to the protocol of Figure 2.

Of course, the present invention is susceptible of various changes and modifications which will occur to the skilled person. In particular, the present invention has been described in connection with a transmission of messages from the monitoring circuit to the analysis tool, but it applies the same to a transmission of messages in the opposite direction.

Furthermore, the present invention has been described in relation to particular values ​​MSEO code, but these values ​​may be modified or reversed.