SPI Handler/Driver (Spi) for External ICs - MCAL & Driver Development

SPI MCAL Concepts

AUTOSAR SPI Hierarchy

AUTOSAR SPI driver organises communication in three levels:

Channel: a logical data buffer for one piece of data (e.g., 16-bit sensor register read). Defines data width, transfer type, default transmit value.
Job: one complete SPI transaction to one device (CS assert + N channel transfers + CS deassert). Defines which channels, which CS pin, which SPI bus.
Sequence: an ordered list of Jobs to execute. Jobs in a sequence may share or not share CS. Sequences can be synchronous (blocking) or asynchronous (with callback).

Channel, Job, Sequence Hierarchy

SPI Hierarchy Example: TLE7242 Gate Driver

  Sequence: SEQ_TLE7242_MONITOR (async, periodic)
      |
      +-- Job: JOB_TLE7242_READ_STATUS
      |       CS: SPI0_CS0 (TLE7242 chip select)
      |       Channels:
      |         CH_CMD:    8-bit command byte (0x00 = read status)
      |         CH_STATUS: 16-bit status response
      |
      +-- Job: JOB_TLE7242_WRITE_CONFIG
              CS: SPI0_CS0
              Channels:
                CH_CMD:    8-bit command byte (0x80 = write config)
                CH_DATA:   16-bit config value

  Hardware: QSPI0 (on TC387)
  Baud rate: 2 MHz
  Frame format: CPOL=0 CPHA=1 (Mode 1)
  CS polarity: active low

SPI Channel/Job/Sequence Configuration

Cspi_cfg_tle7242.c

/* SPI configuration: TLE7242 gate driver monitoring */
#include "Spi.h"

/* --- Channels --- */
const Spi_ChannelConfigType Spi_ChannelConfig[] = {
    {
        .SpiChannelId     = SPI_CH_TLE7242_CMD,
        .SpiDataWidth     = 8u,           /* 8-bit command */
        .SpiTransferStart = SPI_MSB_FIRST,
        .SpiDefaultData   = 0x00u,        /* sent during read phase */
        .SpiEbMaxLength   = 1u,
    },
    {
        .SpiChannelId     = SPI_CH_TLE7242_STATUS,
        .SpiDataWidth     = 16u,          /* 16-bit status response */
        .SpiTransferStart = SPI_MSB_FIRST,
        .SpiDefaultData   = 0x0000u,
        .SpiEbMaxLength   = 1u,
    },
};

/* --- Jobs --- */
const Spi_JobConfigType Spi_JobConfig[] = {
    {
        .SpiJobId         = SPI_JOB_TLE7242_READ,
        .SpiHwUnit        = SPI_HW_UNIT_QSPI0,
        .SpiBaudrate      = 2000000u,     /* 2 MHz */
        .SpiCsIdentifier  = SPI_CS_TLE7242,
        .SpiCsPolarity    = SPI_CS_ACTIVE_LOW,
        .SpiDataShiftEdge = SPI_DATA_SHIFT_LEADING,  /* CPOL=0 CPHA=1 */
        .SpiChannelList   = {SPI_CH_TLE7242_CMD, SPI_CH_TLE7242_STATUS},
        .SpiJobEndNotification = Spi_TLE7242_ReadComplete,
    },
};

/* --- Sequences --- */
const Spi_SequenceConfigType Spi_SequenceConfig[] = {
    {
        .SpiSequenceId    = SPI_SEQ_TLE7242_MONITOR,
        .SpiJobList       = {SPI_JOB_TLE7242_READ},
        .SpiSeqEndNotification = NULL_PTR,
        .SpiInterruptibleSequence = FALSE,  /* not interruptible */
    },
};

/* Usage: trigger async SPI transfer */
void TLE7242_Monitor_10ms(void)
{
    uint8 cmd = 0x00u;  /* read status command */
    Spi_SetupEB(SPI_CH_TLE7242_CMD, &cmd, NULL_PTR, 1u);
    Spi_AsyncTransmit(SPI_SEQ_TLE7242_MONITOR);
    /* Callback Spi_TLE7242_ReadComplete() fires when done */
}

Summary

The AUTOSAR SPI Channel/Job/Sequence hierarchy is more complex than raw SPI register programming, but it enables sophisticated patterns: a Sequence can contain multiple Jobs to different devices, executing them back-to-back with the SPI bus dedicated to that Sequence. Async SPI (Spi_AsyncTransmit) is the preferred mode for production code because it frees the CPU while the DMA handles the data transfer, with a callback firing on completion. Sync SPI (Spi_SyncTransmit) blocks the calling task until the transfer completes - acceptable for startup initialisation of external ICs, but must never be called from a high-priority task in production.

🔬 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.