Abbreviations

DCM – Diagnostic Communication Manager
CDD -Candela Diagnostic Description
NRC -Negative Response Code
RCRRP – Request Correctly received Response Pending

Introduction

In a AUTOSAR project, the Diagnostics CDD integration process shall generate most of the configuration information necessary for Diagnostics Communication Manager (DCM) and its dependencies. In addition, service specific user call-out functions are generated. The implementation for these call-outs must be filled by the application programmer for correct functionality.

Basic operation

When a diagnostics service is requested by diagnostics tester, DCM will interpret the request and invoke a user call-out function associated with the service and its sub-function.

The signature of call-out function looks something like this. The naming of the function may differ , however the logic remain same.

Std_ReturnType <Module>_<DataMember>_<service>( const uint8 * Data,
Dcm_OpStatusType OpStatus, Dcm_NegativeResponseCodeType * ErrorCode );

Example call-out for write data by identifier service will look something like this. SpeedLimter is the module name. MaxSpeed is data member to be written.

Std_ReturnType DataServices_SpeedLimter_MaxSpeed_WriteData(const uint8 * Data,
Dcm_OpStatusType OpStatus,
Dcm_NegativeResponseCodeType * ErrorCode);

opStatus

As each service requires a processing time, Dcm shall call these call-out with different opStatus values, so that kind of state machine can be realized. Please note call-outs originate from Dcm_MainFunction context.

When service requested by diagnostic tester, then …

1. DCM invokes respective call-out handler, first with opStatus equal to DCM_INITIAL.
2. When processing is not completed in the first call & return status is DCM_E_PENDING, then DCM invokes the call-out handler with opStatus equal to DCM_PENDING on every Dcm_MainFunction context as long as the rerun status from call-out us DCM_E_PENDING.
3. When processing is not completed in the first call & return status is DCM_E_FORCE_RCRRP, then DCM defer invoking the call-out handler until RCRRP timeout. At RCRRP timeout, it call-out invoked with opStatus equal to DCM_FORCE_RCRRP_OK from Dcm_MainFunction context.
4. In case DCM detected internal timeout on operation, DCM invokes the call-out handler with opStatus equal to DCM_CANCEL.

Here is one possible illustration of opStatus.

Possible return values from the call-out and reaction of DCM.

The standard return (Std_ReturnType) value of these callout functions are

1. E_OK – Request was successful
2. E_NOT_OK – Request was not successful
3. DCM_E_PENDING – Request is not yet finished
4. DCM_E_FORCE_RCRRP – Application requests the transmission of a response Response Pending (NRC 0x78)

Std_ReturnType::E_OK
Informs the DCM to send positive response to tester.

Std_ReturnType::E_NOT_OK
Informs the DCM to send negative response to tester. The negative response code given to tester is equal to parameter value ErrorCode.

Std_ReturnType::DCM_E_PENDING
Informs the DCM that processing is not completed. DCM must invoke the call-out again but with opStatus DCM_PENDING. DCM takes care of maintaining protocol timings towards tester.

Std_ReturnType::DCM_E_FORCE_RCRRP
Explicitly requests DCM to send response pending negative response to tester. The next invocation of call-out is deferred until the RCRRP timeout.
On RCRRP timeout, DCM invokes the call-out function with opStatus equal to DCM_FORCE_RCRRP_OK.

Negative Response Codes

Here is the list of few frequently used NRC.

• DCM_POS_RESP 0x00
• DCM_E_GENERALREJECT 0x10
• DCM_E_REQUESTOUTOFRANGE 0x31
• DCM_RESPONSE_PENDING 0x78

Please refer to SWS document [1] for comprehensive list of values of Dcm_NegativeResponseCodeType.

Tag references

SWS_Dcm_00527: DCM_INITIAL
SWS_Dcm_00530: DCM_PENDING
SWS_Dcm_00529: DCM_FORCE_RCRRP_OK
SWS_Dcm_00980: Dcm_NegativeResponseCodeType

References:

1. Specification of Diagnostic Communication Manager

Follow up article : Diagnostics service – immediate response