MCUSW
Gpt Design Document

Introduction

Overview

The figure below depicts the AUTOSAR layered architecture as 3 distinct layers, Application, Runtime Environment (RTE) and Basic Software (BSW). The BSW is further divided into 4 layers, Services, Electronic Control Unit Abstraction, MicroController Abstraction (MCAL) and Complex Drivers.

autosar_acrhitecture_common.png
AUTOSAR Architecture

MCAL is the lowest abstraction layer of the Basic Software. It contains software modules that interact with the Microcontroller and its internal peripherals directly. Gpt driver is part of the Microcontroller Drivers (block, show above). Below shows the position of the Gpt driver in the AUTOSAR Architecture.

autosar_acrhitecture_gpt.png
AUTOSAR Architecture – GPT MCAL

GPT Overview

Gpt primarily used to generate different time bases that other modules of AUTOSAR could depend on. TDA4x class of devices includes multiple timers, below listed are some of the key features provided.

  • Free running 32 bit up counter
  • Auto reload mode (can be used for continuous counter operation)
  • Support dynamic Start / Stop counter operation
  • Programmable clock dividers (2n, where n = [0-8])
  • 2 timers modules could be operated in cascaded mode to provide 64bit counter
  • Programmable interrupt generation on overflow, compare and capture
  • Programmable clock source

Supports 3 basic functional modes Timer mode, Capture mode & Compare mode. Refer section (References) for more details on timer operation.

References

Sl No Specification Comment / Link
1 AUTOSAR 4.3.1 AUTOSAR Specification for GPT Driver Intranet Link
2 TDA4x TRM Technical Reference Manual, TDA4X Timer module is detailed
3 BSW General Requirements / Coding guidelines Intranet Link
4 Software Product Specification (SPS) Intranet Link Requirements are derived from 1

Requirements

The Gpt driver shall implement as per requirements detailed in 4, 1 and 3. It’s recommended to refer 1 for clarification.

Features Supported

Below listed are some of the key features that are expected to be supported

  • Starting and stopping of hardware timers
  • Getting the timer values
  • Setting one shot mode or continuous mode
  • Controlling time triggered interrupt notifications
  • Controlling time triggered wakeup interrupts
  • The requirement id’s listed below shall be supported
Design ID DES_GPT_001
Requirements Covered MCAL-2123, MCAL-955, MCAL-920, MCAL-921, MCAL-922, MCAL-923, MCAL-925, MCAL-929, MCAL-930, MCAL-932, MCAL-933, MCAL-937, MCAL-938, MCAL-939, MCAL-942, MCAL-947, MCAL-980, MCAL-945, MCAL-1056

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caution.png

Features Not Supported / NON Compliance

  • [NON Compliance] Gpt PreDef Timers is not supported
  • [NON Compliance] GptClockReference doesn’t refer to McuClockReferencePoint. Refer section (Constraints) for details.
  • Standard AUTOSAR GPT specification 1, categorizes few BSW General Requirements as non-requirements, please refer MCAL-2124 for details
  • Supports additional configuration parameters, refer section (Implementation specific parameters (computed)) & (Gpt_RegisterReadback)
Design ID DES_GPT_002
Non Requirements MCAL-2124, MCAL-2080, MCAL-2079, MCAL-2110, MCAL-2109, MCAL-2108, MCAL-2107, MCAL-2106, MCAL-2105, MCAL-2104, MCAL-2103, MCAL-2102, MCAL-2101, MCAL-2007, MCAL-2001, MCAL-2001, MCAL-1991, MCAL-1983, MCAL-1982, MCAL-1981, MCAL-1980, MCAL-1979, MCAL-1948, MCAL-1947

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Assumptions

Below listed are assumed to valid for this design/implementation, exceptions and other deviations are listed for each explicitly. Care should be taken to ensure these assumptions are addressed.

  1. The functional clock to the GPT module is expected to be on before calling any GPT module API.
  2. The GPT driver as such doesn’t perform any PRCM programming to get the functional clock.
  3. The clock-source selection for GPT is not performed by the GPT driver, other entities such as SBL, MCAL module MCU shall perform the same.
  4. The GTC hardware present in the SOC shall not be supported as GPT module.

Note that assumption 1 & 2 are specified by AUTOSAR GPT specification and 3 & 4 are device specific assumption.

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Constraints

Some of the critical constraints of this design are listed below

  • Is cases where MCU module is not employed (supported) to configure the clock source for GPT module (refer Assumptions sub-item 3). The GPT module configurator shall refer to MCU clock source as listed in specification.
Design ID DES_GPT_003
Requirements Covered MCAL-1951, MCAL-1960, MCAL-1950

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Design Description

Fundamental Operation

As detailed in the TRM, the timer module generates an interrupt when the counter reaches its maximum value (i.e. 0xFFFFFFFF, for a 32 bit counter). The basic idea is use “Auto Reload” mode of the timer and initial count that could be set (TCRR register). Consider an example where timer is configured to expire after reaching a count of 0x0E000000

gpt_design_timer_not_started.png
Timer not yet started

Following sequence of steps shall be performed, before the timer could be started

  • The initial count of the counter is set to 0xF1FFFFFF (i.e. 0xFFFFFFFF - 0x0E000000)
  • The reload register (TLDR) is set with 0xF1FFFFFF as depicted above
gpt_design_timer_started.png
Timer started
  • Timer is programmed as configured (one shot or continuous mode)
  • The timer is started and the counter (register TCRR), starts counting on every pulse
    • As depicted in above figure, TCRR has moved w.r.t to TLDR
gpt_design_timer_expired.png
Timer expired
  • When the timer expires, the TCRR is loaded with value present in TLDR as show above
  • An interrupt can be triggered at this point
  • The timer would default to as show in figure "Timer not yet started", in continuous mode. Also note that no explicit start would be required
  • In One Shot mode, timer is halted. i.e. TCRR stop counting the count of 0xFFFFFFFF is retained by TCRR

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Dynamic Behavior

States

As detailed in section 7.1 of 1, a timer would be in one of the following states. Initialized, running, stopped, expired. A variable shall be maintained on per channel basis to track and maintain the state. The diagram below shows transitions of states and it’s associated service API’s.

gpt_design_timer_state.png
Timer States : Sourced from AUTOSAR Spec

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Modes of Timer

Refer 1 specifically section 7.1 of the specification for more details

Continuous Mode

gpt_design_timer_mode_conti.png
Mode: Continuous: Sourced from AUTOSAR GPT Driver spec
Design ID DES_GPT_006
Requirements Covered MCAL-1976, MCAL-1975, MCAL-1973
gpt_design_timer_mode_conti_timevalues.png
Continuous mode: expected time value Sourced from AUTOSAR GPT Driver spec
Design ID DES_GPT_007
Requirements Covered MCAL-2018, MCAL-2028

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One Shot Mode

gpt_design_timer_mode_oneshot.png
Mode: One Shot: Sourced from AUTOSAR GPT Driver spec
Design ID DES_GPT_008
Requirements Covered MCAL-1974, MCAL-1973

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Determination of time elapsed

The elapsed time could be computed under following conditions, also Refer 1 specifically “Table 5: Summary: Return values and DET errors of Gpt_GetTimeElapsed”

  • In continuous mode
    • Can be obtained by subtracting Timer Reload Register value (TLDR) from current counter value (TCRR)
  • In One Shot mode
    • Timer is counting
      • Same as “In Continuous mode”
    • Timer expired
      • Can be obtained by subtracting Timer Reload Register value from max value (i.e. 0xFFFFFFFF for 32 bit counter)
Design ID DES_GPT_009
Requirements Covered MCAL-2018

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Determination of time remaining

The elapsed time could be computed under following conditions, also Refer 1 section 1.5 specifically “Table 6: Summary: Return values and DET errors of Gpt_GetTimeRemaining”

  • In continuous mode
    • Can be obtained by subtracting current counter value (TCRR) from max value (i.e. 0xFFFFFFFF for 32 bit counter)
  • In One Shot mode
    • Timer is counting
      • Same as “In Continuous mode”
    • Timer expired
      • Value is always 0
Design ID DES_GPT_010
Requirements Covered MCAL-2028

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Directory Structure

The directory structure is as depicted in figures below, the source files can be categorized under “Driver Implementation” and “Example Application”

Driver Implemented by

  • Gpt.h and Gpt_Irq.h: Shall implement the interface provided by the driver
  • Gpt.c, Gpt_Gptimer.c, Gpt_Irq.c and Gpt_Priv.h: Shall implement the driver functionality

Example Application

  • Gpt_Cfg.h and Gpt_Cfg.c: Shall implement the generated configuration for pre-compile variant
  • Gpt_PBcfg.c: Shall implement the generated configuration for post-build variant
  • GptApp.c and GptApp.h: Shall implement the example application that demonstrates the use of the driver
gpt_design_timer_dir.png
Directory Structure
gpt_design_timer_dir_detailed.png
Detailed Directory Structure
Design ID DES_GPT_011
Requirements Covered MCAL-1972, MCAL-1971, MCAL-1970

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Configurator

The AUTOSAR GPT Driver Specification details mandatory parameters that shall be configurable via the configurator. Please refer section 10 of 1

Design ID DES_GPT_012
Requirements Covered MCAL-1945, MCAL-1969, MCAL-1968, MCAL-1967, MCAL-1966, MCAL-1965, MCAL-1964, MCAL-1963, MCAL-1962, MCAL-1961, MCAL-1960, MCAL-1959, MCAL-1958, MCAL-1957, MCAL-1956, MCAL-1955, MCAL-1954, MCAL-1953, MCAL-1952, MCAL-1951, MCAL-1950, MCAL-1949, MCAL-1946, MCAL-1945, MCAL-4175

NON Standard configurable parameters

Following lists this design’s specific configurable parameters

Parameter Usage comment
GptDefaultOSCounterId This shall allow integrators to specify the OS counter instance to be used in OS API GetCounterValue () The driver shall implement timed-wait for all waits (e.g. waiting for reset to complete). This timed wait shall use OS API GetCounterValue ()
GptDeviceVariant This shall allow integrators to select the device variant for which integration is being performed. This parameter shall be used by driver to impose device specific constraints. The user guide shall detail the device specific constraints
GptChannelPrescale This parameter per channel and as part of container “GptChannelConfigSet” will allow user to scale the FCLK

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Implementation specific parameters (computed)

The configurator shall determine the maximum number of channels that are configured and generate a macro to define the same. This shall be used to perform range checks on channel configurations and channel ID provided at driver initialization time. Refer section (MACROS, Data Types & Structures)

Variant Support

The driver shall support both VARIANT-POST-BUILD & VARIANT-PRE-COMPILE

Design ID DES_GPT_014
Requirements Covered MCAL-1945

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Dependency on other modules

In addition to dependencies listed in section 5 of 1, GPT driver shall depend on these modules to realize the required functionality. GPT uses Timer hardware present in the device to realize the functionality, this peripheral requires 2 different clock to be operational, namely ICLK and FCLK.

SBL

  • ICLK: Is interface clock required for internal operation of the peripheral. This is not expected to change and typically programmed by SBL, please refer the device specific manual for details and valid value.
  • FCLK: Is functional clock, used to drive the counter of the timer module. As per AUTOSAR GPT module specification 1, the GPT driver shall refer MCU Clock reference point. As detailed in section (Constraints), other entity would require to select the right clock source for the peripheral.
Design ID DES_GPT_015
Requirements Covered MCAL-1950

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Error Classification

Errors are classified in two categories, development error and runtime / production error.

Development Errors

Type of Error Related Error code Value (Hex) Refer Req
API service called without module initialization GPT_E_UINIT 0x0A MCAL-2512
API service for initialization is called when already initialized GPT_E_ALREADY_INITIALIZED 0x0D MCAL-2515
API error return code: Init function failed GPT_E_INIT_FAILED 0x0E MCAL-2516
API parameter checking: invalid channel GPT_E_PARAM_CHANNEL 0x14 MCAL-2517
API parameter checking: invalid value GPT_E_PARAM_VALUE 0x15 MCAL-2518
API parameter checking: invalid pointer GPT_E_PARAM_POINTER 0x16 MCAL-2519
API parameter checking: invalid mode GPT_E_PARAM_MODE 0x1F MCAL-2520
Design ID DES_GPT_037
Requirements Covered MCAL-2512, MCAL-2515, MCAL-2516, MCAL-2517, MCAL-2518, MCAL-2519, MCAL-2520

Error Detection

The detection of development errors is configurable (ON / OFF) at pre-compile time. The switch GptDevErrorDetect will activate or deactivate the detection of all development errors.

Error notification (DET)

All detected development errors are reported to Det_ReportError service of the Development Error Tracer (DET).

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Runtime Errors

The following runtime/production errors shall be detectable by Gpt driver.

Type of Error Related Error code Value (Hex)
API service is called when timer channel is still busy GPT_E_BUSY 0x0B

Error notification (DEM)

All detected run time errors shall be reported to Det_ReportRuntimeError () service.

Design ID DES_GPT_017
Requirements Covered MCAL-2100, MCAL-2094, MCAL-2093, MCAL-2087, MCAL-2086, MCAL-2077, MCAL-2076, MCAL-2067, MCAL-2066, MCAL-2065, MCAL-2060, MCAL-2059, MCAL-2058, MCAL-2053, MCAL-2052, MCAL-2049, MCAL-2045, MCAL-2044, MCAL-2043, MCAL-2042, MCAL-2036, MCAL-2035, MCAL-2027, MCAL-2026, MCAL-2016, MCAL-2015, MCAL-2003, MCAL-1993, MCAL-1984, MCAL-2513 MCAL-4177, MCAL-4176

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Resource Behavior

  • Code Size : Implementation of this driver shall not exceed 5 kilo lines of code and 1 KB of data section.
Design ID DES_GPT_004
Requirements Covered MCAL-2126
  • Stack Size : Worst case stack utilization shall not exceed 2 kilo bytes.
Design ID DES_GPT_005
Requirements Covered MCAL-2125

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Low Level Definitions

The detailed API and interface description is available as part of 1 & 4. This section describes the API supported by the MCAL driver and the requirements covered by each of the API.

MACROS, Data Types & Structures

The sections below lists some of key data structures that shall be implemented and used in driver implementation

Maximum number of channels

Type Identifier Comments
uint32 GPT_MAX_CHANNELS Defines the maximum number of channels that are configured. Its required that configurations for all channel specified is valid.

Gpt_ValueType

Used to specify the timer ticks, please refer section 8.3.2 of 1

Gpt_ModeType

Enumeration, refer section 8.3.4 of 1

Gpt_PredefTimerType

Enumeration, refer section 8.3.5 of 1

Gpt_NotifyType

Is a function pointer with prototype as void Gpt_Notification_<channel> ( void )” . The “_channel” postfix is provided by integrators via the configurator. “_channel” is used by applications to uniquely identify the GPT channel. Refer section 8.7.3.1 of 1

Gpt_ChannelMode

Refer section 10.6.2 of 1

Gpt_RegisterReadbackType

Name Type Range Comments
gptRev uint32 0 to 0xFFFFFFFF H/W version identifier, will not change for a given SoC
gptTtgr uint32 0 to 0xFFFFFFFF Shall always read 0xFFFFFFFF
gptTimerSynCtrl uint32 0 to 0xFFFFFFFF Interface control register, will read 0x00000000

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Gpt_ChannelConfigType

Used to define channel specific parameters for, one channel and the values of these are expected to be populated by configurator.

Type Variable Name Comments
uint32 channelId Used to identify the channel (instance of timer (h/w) in implementation
Gpt_ChannelMode channelMode Used to specify the mode of channel
uint32 tickValueMax Maximum value in ticks, the timer channel is able to count. With the next tick, the timer rolls over to zero
uint8 enableWakeupFlag Flag indicating, if wakeup functionality is to be supported on this channel
Gpt_NotifyType fnPtrNotifyFunction Pointer to function, which shall be called to notify. Expected to be populated by the configurator
uint8 wakeupSourceRef Value that shall be passed as function argument, when wakeup event occurs
uint32 prescale The peripheral provide ability to scale function clock (FCLK), this parameter shall define scaling factor for this clock. The value/range would be device specific, check with device TRM for details.
Design ID DES_GPT_018
Requirements Covered MCAL-2119, MCAL-2114, MCAL-1990, MCAL-1989, MCAL-1988, MCAL-1961, MCAL-1959, MCAL-1958, MCAL-1955, MCAL-1953, MCAL-1952

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Gpt_ConfigType

Used to define all channels specific parameters, shall be supplied to Gpt_Init () function. Values of these are expected to be populated by configurator.

Type Variable Name Comments
Gpt_ChannelConfigType * channelCfgPtr Is a constant pointer, pointing to all channel specific parameters. For “VARIANT-PRE-COMPILE” an instance of this structure shall instantiated in Gpt_Cfg.c by the configurator and driver implementation shall refer directly. Consider naming this variable as GptChannelConfigSet_PC For “VARIANT-POST-BUILD” an pointer of this type shall be provided to Gpt_Init () function.
Design ID DES_GPT_019
Requirements Covered MCAL-1987

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Gpt_ConfigChannelType_PC (only if implementing v AUTOSAR 4.3.1)

Used to define all channels identifiers, values of these are expected to be populated by configurator.

Type Variable Name Comments
Gpt_ChannelType channelId[GPT_MAX_CHANNELS] Shall contain channel identifiers for all channels. For “VARIANT-PRE-COMPILE” an instance of this structure shall instantiated in Gpt_Cfg.c by the configurator and driver implementation shall refer directly. Consider naming this variable as GptChannelIdConfig_PC. For “VARIANT-POST-BUILD”, this shall not be used, i.e. Gpt_Init (NULL_PTR)
Design ID DES_GPT_020
Requirements Covered MCAL-1987, MCAL-1954

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API's

For the standard API's please refer 8.3 of 1. Sections below highlight other design considerations for the implementation.

Gpt_Init

Refer section 8.3.2 of 1

Design ID DES_GPT_021
Requirements Covered MCAL-2006, MCAL-2005, MCAL-2004, MCAL-2003, MCAL-2002, MCAL-2000, MCAL-1999, MCAL-1998, MCAL-1997, MCAL-1996, MCAL-1995, MCAL-1994

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Gpt_DeInit

Refer section 8.3.3 of 1

Design ID DES_GPT_022
Requirements Covered MCAL-2017, MCAL-2016, MCAL-2015, MCAL-2014, MCAL-2013, MCAL-2012, MCAL-2011, MCAL-2010, MCAL-2009, MCAL-2008, MCAL-1964

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Gpt_GetTimeElapsed

Refer section 8.3.4 of 1

Design ID DES_GPT_023
Requirements Covered MCAL-2027, MCAL-2026, MCAL-2025, MCAL-2024, MCAL-2023, MCAL-2022, MCAL-2021, MCAL-2020, MCAL-2019, MCAL-2018, MCAL-1966

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Gpt_GetTimeRemaining

Refer section 8.3.5 of 1

Design ID DES_GPT_024
Requirements Covered MCAL-2028, MCAL-2029, MCAL-2030, MCAL-2031, MCAL-2032, MCAL-2033, MCAL-2034, MCAL-2035, MCAL-2036, MCAL-1967

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Gpt_StartTimer

Refer section In addition to details provided in 8.3.6 of 1 following design shall be implemented.

  • Interrupt shall be enabled for channels, for which the notification or wake-enable is enabled.
  • The timer operating in ONE-SHOT mode the interrupt shall be enabled, irrespective of the enabled/disabled notification. As ISR would be right place to mark the channel as EXPIRED, otherwise the API’s like Gpt_GetTimeRemaining () and Gpt_ElapsedTime () would require special handling for EXPIRED timers.
Design ID DES_GPT_025
Requirements Covered MCAL-2045, MCAL-2044, MCAL-2043, MCAL-2042, MCAL-2041, MCAL-2040, MCAL-2039, MCAL-2038, MCAL-2037

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Gpt_StopTimer

Refer section 8.3.7 of 1

Design ID DES_GPT_026
Requirements Covered MCAL-2053, MCAL-2052, MCAL-2051, MCAL-2050, MCAL-2049, MCAL-2048, MCAL-2047, MCAL-2046

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Gpt_EnableNotification

Refer section 8.3.8 of 1

Design ID DES_GPT_027
Requirements Covered MCAL-2060, MCAL-2059, MCAL-2058, MCAL-2057, MCAL-2056, MCAL-2055, MCAL-2054, MCAL-1977

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Gpt_DisableNotification

In addition to details provided in 8.3.9 of 1 following design shall be implemented.

  • Interrupt shall be enabled for provided channel, when the channel state is in RUNNING or STOPPED or EXPIRED or INITIALIZED
Design ID DES_GPT_028
Requirements Covered MCAL-2067, MCAL-2066, MCAL-2065, MCAL-2064, MCAL-2063, MCAL-2062, MCAL-2061, MCAL-1965

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Gpt_SetMode

Refer section 8.3.10 of 1

Design ID DES_GPT_029
Requirements Covered MCAL-2078, MCAL-2077, MCAL-2076, MCAL-2075, MCAL-2074, MCAL-2073, MCAL-2072, MCAL-2071, MCAL-2070, MCAL-2069, MCAL-2068

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Gpt_DisableWakeup

Refer section 8.3.11 of 1

Design ID DES_GPT_030
Requirements Covered MCAL-2087, MCAL-2086, MCAL-2085, MCAL-2084, MCAL-2083, MCAL-2082, MCAL-2081, MCAL-1969

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Gpt_EnableWakeup

Refer section 8.3.12 of 1

Design ID DES_GPT_031
Requirements Covered MCAL-2094, MCAL-2093, MCAL-2092, MCAL-2091, MCAL-2090, MCAL-2089, MCAL-2088, MCAL-1978, MCAL-1969

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Gpt_CheckWakeup

Refer section 8.3.13 of 1

Design ID DES_GPT_032
Requirements Covered MCAL-2100, MCAL-2099, MCAL-2098, MCAL-2097, MCAL-2096, MCAL-2095, MCAL-1969

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Gpt_GetVersionInfo

Refer section 8.3.1 of 1

Design ID DES_GPT_033
Requirements Covered MCAL-1992, MCAL-1993, MCAL-1968

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Gpt_RegisterReadback

As noted from previous implementation, the timer configuration registers could potentially be corrupted by other entities (s/w or h/w). One of the recommended detection methods would be to periodically read-back the configuration and confirm configuration is consistent. The service API defined below shall be implemented to enable this detection.

Description Comments
Service Name Gpt_RegisterReadback Can potentially be turned OFF
Syntax Std_ReturnType Gpt_RegisterReadback(Gpt_ChannelType GptChannel, Gpt_RegisterReadbackType *RegRbPtr) Gpt_RegisterReadbackType defines the type, that holds critical values, refer below
Service ID 0x0F
Sync / Async Sync
Reentrancy Non Reentrant
Parameter in GptChannel Identifies a unique valid channel
Parameters out RegRbPtr A pointer of type Gpt_RegisterReadbackType, which holds the read back values
Return Value Standard return type E_OK or E_NOT_OK in case of invalid channel id

The critical register listed is a recommendation and implementation shall determine appropriate registers.

This service could potentially be turned OFF in the configurator.

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Notify ISR

On elapse of configured count, the timer peripheral generates an interrupt. The implementation shall provide an ISR with prototype as “void Gpt_<ChannelNum>Isr (void)” The control flow shall be as depicted in flow chart figure below. Since, the function prototype dosen’t take any arguments to uniquely identify the timer channel that caused this interrupt, a separate ISR shall be implemented for each configured / enabled channel.

gpt_design_timer_isr.png
Notify ISR Flow chart
Design ID DES_GPT_034
Requirements Covered MCAL-2118, MCAL-2117, MCAL-2116, MCAL-2115, MCAL-2113, MCAL-2112

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Wakeup ISR

On elapse of configured count the timer peripheral generates an interrupt. The implementation shall provide an ISR with prototype as “void Gpt_<ChannelNum>Isr (void)” The control flow shall be as depicted in flow chart above, with following exceptions

  1. Check for notify & call notify shall not be implemented, instead EcuM_CheckWakeup () shall be called with configured wakeup source
  2. Check for mode and its associated action for true condition shall not be implemented
Design ID DES_GPT_035
Requirements Covered MCAL-2111, MCAL-2122, MCAL-1986

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Global Variables

This design expects that implementation will require to use following global variables.

Variable Type Description Default Value
Gpt_DrvStatus uint32 Initialization status of the driver is maintained FALSE
Gpt_DrvObj Gpt_DriverObjType GPT driver object, local to the implementation and scope shall NOT be limited to Gpt.c Un defined
Gpt_WakeupSourceType EcuM_WakeupSourceType Used to store the WakeupSource Ref value for all configured channels. Local to the driver implementation and scope shall be limited to Gpt.c Un defined
Gpt_IsrFxn Gpt_IsrRefType Array of pointers to the call notification and wakeup Functions Un defined
Design ID DES_GPT_036
Requirements Covered SWS_BSW_00130

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Decision Analysis & Resolution (DAR)

Sections below list some of the important design decisions and rational behind those decision.

Use of DM Timer Auto-Reload mode for GPT continuous mode

The timer hardware doesn’t support continuous mode if configured timer count is less than max count of timer (0xFFFFFFFF in 32 bit timer). To implement GPT continuous mode we have to use timer interrupt to trigger timer start or tweak timer configuration during timer start to work in Continuous mode.

DAR Criteria

Implementation of GPT ‘Continuous’ mode, without timing constraints (or programming registers in ISR)

Available Alternatives

  • Use GPT count completion interrupt to restart timer. For implementing continuous mode with this count provided to start timer function will be programmed as to match value for interrupt generation and timer will start counting from zero. Once it reaches count value it will generate match interrupt. Same will be used for notification and wake up event. Here driver will check if timer is configured in continuous mode and if yes it will trigger timer enable again.
    • Advantages:
      • Simple to implement. No overhead configuration.
    • Disadvantages:
      • Latency between timer interrupt generation and timer restart. This will be major issue as it will vary with Processor speed. Also will not be constant between two timer count completion cycles.
      • Dependency on ISR for timer restart
  • Use of Timer auto reload mode Device timer HW supports auto-reload mode when timer overflow (max count possible for timer HW reached) occurs. In this case timer HW restarts timer with value loaded in Counter register (CR). To use this feature for GPT continuous mode we need to calculate count value with reference to max count. For example if count value is 0x10 then counter register should be programmed with (0xFFFF_FFFF – 0x10) value. This will ensure timer restarts after counting till overflow.
    • Advantages:
      • No dependency on ISR for timer restart. This will be taken care by hardware.
      • Independent of processor speed.
    • Disadvantages: Complex software implementation as software has to make sure correct value is written and also keep track of count value given by application for timer elapsed and time remaining functions.

Decision

To avoid dependency on processor and interrupt service routine, recommended to use timer hardware auto-reload feature. Software will make sure to return correct values for time elapsed and time remaining functions.

Design ID DES_GPT_037
Requirements Covered MCAL-1976, MCAL-1975, MCAL-1973

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Test Criteria

The sections below identify some of the aspects of design that would require emphasis during testing of this design implementation

  • State Transitions
    • Test cases shall exercise all state transitions as detailed in section (States)
    • Ensure non supported API’s in a given state, returns valid error code
  • Wake functionality
    • Test cases shall ensure, wake up functionality is exercised on one channel at least
  • Mode
    • Test cases shall ensure, a timer shall be operable in all supported modes (but not concurrently, for a single channel)
  • Concurrency
    • Test cases shall ensure, multiple channels can be operated concurrently
  • Timeout
    • Test cases exercising Gpt_Start API, as perform equivalence class test on Gpt_ValueType Gpt_Start (). As a large Gpt_ValueType increase test cycle time
    • Large Gpt_ValueType shall be performed only for “Full Test Cycle”
  • Elapsed / Remaining time
    • Test cases shall ensure API (when available) GptTimeElapsedApi () is invoked on elapsed timer (one shot mode) and value shall not change
    • Test cases shall ensure API (when available) GptTimeRemainingApi () is invoked on elapsed timer (one shot mode) and value shall not change

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Document Revision History

Revision Date Author Description Status
0.1 25 July 2018 Sujith S First version Pending Review
0.2 01 Oct 2018 Sujith S Format conversion and review completed Approved
0.3 28 Dec 2018 Sujith S Updated section "Development Errors" to include requirement mapping Approved
0.4 19 Jan 2020 Sunil M S Updates w.r.o porting AUTOSAR 4.3.1 Version Approved