1 Introduction
2 Communication
3 Debugging
- 3.1 Disabling Peer-Loss Detection
- 3.2 General Debugging procedure

Introduction

Some general question regarding the product are covered in the Frequently Asked Questions section: FAQ & Troubleshooting . In this document methods for debugging and checking proper functionality of the communication between application and communication module shall be shown.

Communication

Basics

Following table shows the basic structure of the SPI frame.

Range	Length	Description

Range	Length	Description
0 .. 3	4 byte	MCTC SPI Header
4 .. 76	73 byte	cyclic data (data mapper)
77 .. 126	50 byte	RPC data
127	1 byte	reserved

The block MCTC SPI Header contains the following elements:

/**< SPI cyclic data header */
typedef struct {
    uint16_t crc_le16;                          /**< checksum */
    uint8_t seq;                                /**< sequence number */
    uint8_t lenData;                            /**< data length */
} GOAL_MI_MCTC_SPI_CYCLIC_T;

The field crc_le16 contains a checksum (Fletcher-16, Wikipedia) with a starting value of 0x0007. The field seq contains a sequence counter which increases with each updated frame. The field lenData contains the length of valid data after the MCTC header..

With an attached Logic Analyzer, it is possible to check the header for valid values. The third value (0x89) is the incrementing sequence number and the fouth byte shows the actual length of data (0x7C or 124).

Is the application controller receiving valid frames?

If incoming frames from the communication module can be checked by content, following hints should determine wether valid frames are received:

The first 2 bytes (crc) contains a value != 0
The 3rd byte changes with each frame (cyclic counter)
The 4th byte (length) has a value != 7

Programmatically, valid frames are detected by checking the CRC field in the header.

For uGOAL this is determined within sapi.c:

/****************************************************************************/
/** Basic cyclic communication function
 *
 * This function initiates SPI transfer and dispatches received data to
 * upper layers data callback and RPC handling.
 *
 */
void sapi_loop(
        void
)
{
    /* update frame header */
    sapi_pdUpdateHeader(sendData, GOAL_MI_MCTC_LEN - sizeof(GOAL_MI_MCTC_SPI_CYCLIC_T));

    /* transfer data via SPI */
    plat_spiTransfer((const char *) &sendData[0], (char *) receiveData, BUF_LENGTH);

    /* control LED if Connection valid or Wink active */
    if (true == sapi_pdCheckHeader(receiveData, GOAL_MI_MCTC_LEN - sizeof(GOAL_MI_MCTC_SPI_CYCLIC_T))) {

        /* inform application */
        som_dataCb(&receiveData[0], &sendData[0]);

        /* trigger RPC */
        goal_miMctcDmCbRead();
   }
}

If line 22 within the function sapi_loop is executed, valid frames from the communication module are received.

For GOAL based applications this can be determined in the function goal_miMctcSpiProcessTask within the goal_mi_mctc_spi.c module:

        do {

            /* check frame CRC */
            res = goal_miMctcCrc(&pBufSpi[sizeof(GOAL_MI_MCTC_SPI_CYCLIC_T)], pHdr->lenData, GOAL_le16toh_p(&pHdr->crc_le16));
            if (GOAL_RES_ERR(res)) {
                break;
            }

            /* check sequence counter */
            if (pMiMctcSpi->seqCyclicRem != pHdr->seq) {

                /* inform MI MCTC that connection is running */
                goal_miMctcMonitorRx(pMiMctc, GOAL_TRUE);

                /* re-arm watchdog */
                pMiMctcSpi->tsTout = tsNow + pMiMctc->cfgToutValue;

                /* update seen sequence */
                pMiMctcSpi->seqCyclicRem = pHdr->seq;
            }

            if (pHdr->lenData) {
                /* process MI DM incoming data */
                goal_miDmReadSync(pMiMctcSpi->pMiDmRead, &pBufSpi[sizeof(GOAL_MI_MCTC_SPI_CYCLIC_T)]);
            }
        } while (0);

If the checks shown in the code are performed successfully a valid frame was received.

Manually this could be checked by evaluating the crc from the SPI frame and calculating the expected value over the given data with the given length from the header. The header itself is skipped from crc calculation.

Is the communication module receiving the frames from the application controller?

The communication module will provide valid mCTC frames even if the application controller does not. Thus it is not that easy to determine, if the frames sent by the application controller are evaluated by the communication module.

A good measurement whether the communication module receives the frames from the application controller is the capability to perform the RPC synchronisation. This is executed initially with beginning of the communication.

The RPC synchronisation follows a state machine with the following states:

State	Description

State	Description
GOAL_MI_MCTC_RPC_STATE_INIT	Initial state	Entered initially or in error case
GOAL_MI_MCTC_RPC_STATE_SYNC_REQ	Initial request state	Entered after INIT state
GOAL_MI_MCTC_RPC_STATE_SYNC_ACK_LOCAL	Initial acknowledge state	Entered after SYNC REQ state
GOAL_MI_MCTC_RPC_STATE_SYNC_ACK_REMOTE	Initial sync request was acknowledged	Entered if SYNC request was acknowledged, the peer module received our request!
GOAL_MI_MCTC_RPC_STATE_RUN_ONCE	Setup state after Sync	Entered when SYNC was successful
GOAL_MI_MCTC_RPC_STATE_RUN	Normal operating state	Entered after SYNC is done

If the state GOAL_MI_MCTC_RPC_STATE_SYNC_ACK_REMOTE is entered, the communication module received the frames sent by the application controller.

Following code shows the state machine in exceprts:

Debugging

Disabling Peer-Loss Detection

By default both, the basic SPI communication and the RPC communication, are monitored and in case of loss of communication or a missing response an error is detected and propagated. This will stop the system from working any further. This can be disabled for debugging purpose. However this should never be done in a productive system, since this will mask potential communication problems.

For uGOAL application, the following defines need to be set in goal_config.h:

or using the make system, using the command in a project directory, like ugoal/projects/ugoal/02_profinet/gcc:

and building the project:

For GOAL based application, following code needs to be called before any other functions. So best place the following calls in appl_init():

This will disable both the RPC timeout and the SPI communication timeout. If the application controller is halted for an arbitrary time, operation can be resumed without any error.

General Debugging procedure

If debugging an application some precautions need to be considered. The correct sequence for debugging a application would be:

stop the application (on the application controller)
reset the SoM module (e.g. using the reset button on the arduino shield)
start debugging of the application (application controller)
run the application

Then the application should be able to start the communication module as required.

SoM/iRJ45

007 - mCTC Debugging and Trouble Shooting