InputOutputControlByIdentifier (0x2F) - UDS Diagnostics

0x2F InputOutputControlByIdentifier Service

controlOptionRecord	Value	Action
returnControlToECU	0x00	Release the controlled output; ECU resumes normal control
resetToDefault	0x01	Set output to its default/safe value; ECU retains control
freezeCurrentState	0x02	Hold current output value; ECU stops updating it
shortTermAdjustment	0x03	Set output to value in controlEnableRecord; ECU overrides for test duration

AUTOSAR DCM: IO Control Implementation

CDcm_IoControl.c

/* 0x2F InputOutputControlByIdentifier: control cooling fan via DID 0x0210 */
#include "Dcm.h"
#include "IoHwAb.h"

/* IoControl states */
typedef enum { IOCTRL_ECU=0, IOCTRL_OVERRIDE } IoCtrl_State_t;
static IoCtrl_State_t g_fanCtrlState = IOCTRL_ECU;
static uint8 g_fanOverrideDuty = 0;

Std_ReturnType DcmDspData_CoolingFan_ReturnControlToECU(
    Dcm_OpStatusType OpStatus, Dcm_NegativeResponseCodeType* ErrorCode)
{
    g_fanCtrlState = IOCTRL_ECU;  /* release override */
    return E_OK;
}

Std_ReturnType DcmDspData_CoolingFan_ShortTermAdjustment(
    const uint8* ControlStateInfo, Dcm_OpStatusType OpStatus,
    Dcm_NegativeResponseCodeType* ErrorCode)
{
    uint8 duty = ControlStateInfo[0];   /* 0–100% duty cycle */
    if (duty > 100) {
        *ErrorCode = DCM_E_REQUESTOUTOFRANGE;
        return E_NOT_OK;
    }

    /* Safety: check vehicle speed — do not allow fan control at high speed */
    if (Rte_IRead_DcmWrapper_VehicleSpeed_kmh() > 10u) {
        *ErrorCode = DCM_E_CONDITIONSNOTCORRECT;   /* NRC 0x22 */
        return E_NOT_OK;
    }

    g_fanOverrideDuty = duty;
    g_fanCtrlState = IOCTRL_OVERRIDE;
    IoHwAb_SetFanDuty(duty);
    return E_OK;
}

/* Called in application task: apply override or ECU control */
void IoCtrl_MainFunction(void) {
    if (g_fanCtrlState == IOCTRL_OVERRIDE) {
        IoHwAb_SetFanDuty(g_fanOverrideDuty);
    }
    /* ECU state: normal control algorithm runs instead */
}

Safety Architecture for IO Control

IO Control Safety Architecture

  Tester sends: 0x2F 0x0210 0x03 0x64   (shortTermAdjust fan to 100%)
       │
       ▼
  DCM checks:
  ├── Session: ExtendedDiagnostic? ✓
  ├── Security: Level 1 active? ✓
  └── Calls ShortTermAdjustment callback
       │
       ▼
  Application callback checks:
  ├── Input range: duty <= 100? ✓
  ├── Safety precondition: speed < 10 km/h? ✓
  └── Override set; IoHwAb_SetFanDuty(100%)
       │
       ▼
  Safety supervisor (independent):
  ├── S3 timeout (5s no TesterPresent) → session returns to Default
  ├── Default session → DCM calls ReturnControlToECU automatically
  └── Application reads IoCtrl state = ECU → resumes normal fan algorithm

  ASIL-relevant IO (brakes, steering):
  IoControl MUST be prohibited; configure DCM to return NRC 0x22 unconditionally
  Never allow tester override of ASIL safety functions

Summary

IO control is the highest-risk UDS service — it directly actuates hardware. Three mandatory safety layers: session restriction (Extended Diagnostic), security access (Level 1), and application precondition checks (speed, temperature, system state). The returnControlToECU option must always be implemented and tested — it's the recovery path when the tester disconnects or the session times out. ASIL C/D functions (brakes, EPS, airbag) must never be controllable via 0x2F; configure the DCM to return NRC 0x22 unconditionally for those IDs.

🔬 Deep Dive — Core Concepts Expanded

This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.

Key principles to reinforce:

Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.

🏭 How This Topic Appears in Production Projects

Project integration phase: The concepts covered in this lesson are most commonly encountered during ECU integration testing — when multiple software components from different teams are combined for the first time. Issues that were invisible in unit tests frequently surface at this stage.
Supplier/OEM interface: This is a topic that frequently appears in technical discussions between Tier-1 ECU suppliers and OEM system integrators. Engineers who can speak fluently about these details earn credibility and are often brought into critical design review meetings.
Automotive tool ecosystem: Vector CANoe/CANalyzer, dSPACE tools, and ETAS INCA are the standard tools used to validate and measure the correct behaviour of the systems described in this lesson. Familiarity with these tools alongside the conceptual knowledge dramatically accelerates debugging in real projects.

⚠️ Common Mistakes and How to Avoid Them

Assuming default configuration is correct: Automotive software tools ship with default configurations that are designed to compile and link, not to meet project-specific requirements. Every configuration parameter needs to be consciously set. 'It compiled' is not the same as 'it is correctly configured'.
Skipping documentation of configuration rationale: In a 3-year ECU project with team turnover, undocumented configuration choices become tribal knowledge that disappears when engineers leave. Document why a parameter is set to a specific value, not just what it is set to.
Testing only the happy path: Automotive ECUs must behave correctly under fault conditions, voltage variations, and communication errors. Always test the error handling paths as rigorously as the nominal operation. Many production escapes originate in untested error branches.
Version mismatches between teams: In a multi-team project, the BSW team, SWC team, and system integration team may use different versions of the same ARXML file. Version management of all ARXML files in a shared repository is mandatory, not optional.

📊 Industry Note

Engineers who master both the theoretical concepts and the practical toolchain skills covered in this course are among the most sought-after professionals in the automotive software industry. The combination of AUTOSAR standards knowledge, safety engineering understanding, and hands-on configuration experience commands premium salaries at OEMs and Tier-1 suppliers globally.