Using Virtual EEPROM and Flash API for Renesas MCUs (1)

The Solution – Data Flash & Record Management  Use data flash and existing Flash API for low level  Add layer to handle record management Flash API ???. Data Flash Block #0Data Flash B

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Using Virtual EEPROM and Flash API for Renesas MCUs

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Renesas Technology & Solution Portfolio

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Microcontroller and Microprocessor Line-up

44 DMIPS, True Low Power Embedded Security, ASSP

25 DMIPS, Low Power

10 DMIPS, Capacitive Touch

 Industrial & Automotive, 150nm

 190µA/MHz, 0.3µA standby

 Industrial, 90nm

 200µA/MHz, 1.6µA deep standby

 Automotive & Industrial, 90nm

 Automotive & Industrial, 65nm

 600µA/MHz, 1.5µA standby  Automotive, 40nm

 500µA/MHz, 35µA deep standby

 200µA/MHz, 0.3µA deep standby

 1mA/MHz, 100µA standby

 Industrial & Automotive, 130nm

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 Devices in a smart society must efficiently use their available resources Eliminating the need for external components

when they can be incorporated inside the MCU is vital.

‘Enabling The Smart Society’

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ROM

The Problem – Storing Non-Volatile Data

 Store in internal ROM

 Advantages:

 Stored internally to MCU; no extra cost

 Disadvantages:

 Must halt MCU or run from RAM

 Possibility of corrupting application

 Relatively large minimum write and erase sizes

 Complex to implement

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 Store in external EEPROM

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 Store in internal data flash

 Advantages:

 Stored internally to MCU; no extra cost

 Can continue to execute from ROM

 Relatively small minimum write and erase sizes

 No possibility of corrupting ROM

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The Solution – Data Flash & Record

Management

 Use data flash and existing Flash API for low level

 Add layer to handle record management

Flash API

???

Virtual EEPROM

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Data Flash Block #0

Data Flash Block #1

EMPTY

Why is Virtual EEPROM Needed?

 Many data flashes do not have 1-byte writes

 Maintaining multiple records

 Statically allocating addresses can wear out DF faster

 Using advanced features of MCU

Data #1 Data #2 EMPTY

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ROM Data Flash

What is the Virtual EEPROM Project?

 The Virtual EEPROM Project allows you to use the Data Flash

on your MCU as you would an EEPROM while adding other record management features

MCU

ROM Data Flash/VEE

I2C

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Data Flash vs ROM

 Typically Data Flash has:

 Smaller write and erase sizes

 Shorter write times

 Larger number of rewrite/erase cycles

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Virtual EEPROM Features

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Background Operations (BGO)

 With BGO, MCU can continue during DF erase or write

 Memory area being worked on cannot be accessed

Access Violation!

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Wear Leveling

 Increases longevity of the Data Flash

 Records do not overwrite

 Old records are ignored

VEE Memory Area

Address

0x100000

Address 0x1007FF

VEE

Record

1

VEE Record 1

VEE Record 2

VEE Record 1

VEE Record 2

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Ignore Duplicate Writes

 Increases longevity of the Data Flash

 Identical writes are ignored

VEE

VEE Record

1

VEE

VEE Record

VEE Record 2

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Record Caching

 No seeking for records

 1 cache entry per available record number

VEE Memory Area

Address

0x100000

Address 0x1007FF

VEE Record Cache

Record 1 Address

Record 2 Address

VEE Record

VEE Record Many More

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VEE Memory Area

VEE

Record

2

Error Detection

 Each record has its own error detection field

 Virtual EEPROM recovers automatically from errors

 Recovery measures are only taken on writes

VEE Record 1

• ID

• Size

• Data

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 4 extra structure members per record

 Overhead depends on write granularity

 RX62N = 32 bytes per record

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How does it work?

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Virtual EEPROM Terminology

VEE Sector 0

VEE Record 0 VEE Record 1 VEE Record 1 VEE Record 0 VEE Record 2 VEE Record 2

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Virtual EEPROM Operational Overview

VEE Sector 0

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VEE Sector 0

NOT ENOUGH

ROOM

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VEE Sector 0

DEFRAG OCCURS

VEE Record 1

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VEE Sector 0

VEE Record 1 VEE Record 0 VEE Record 2

DEFRAG CONTINUES

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VEE Sector 0

DELETE OLD

BLOCK

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VEE Sector 0

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Virtual EEPROM Configuration

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Why would I need more than 1 VEE Sector?

 Optimize (lower) the number of defrags

VEE Sector #0 – Block #0

VEE Record 1

VEE Record 2

VEE Record 1

VEE Record 2

Defrag Again!

1 Sector

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Why would I need more than 1 VEE Sector?

 Optimize (lower) the number of defrags

VEE Record 1

VEE Record

Defrag Finally!

2 Sectors

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Virtual EEPROM API

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VEE Operation Completion

 Can use polling or interrupt driven

 Polling:

 Use R_VEE_GetState()

 Will return current state of VEE

 Interrupt Driven:

 User defined callback in r_vee_config.h

 Warning: Callback is called from interrupt

#define VEE_CALLBACK_FUNCTION VEE_OperationDone_Callback

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Data Flash User Application

Why do we need R_VEE_ReleaseState()?

 Used to prevent data flash access violations

 R_VEE_Read(ID=0) to read VEE Record 0

 R_VEE_Write(ID=1) to write VEE Record 1

 User reads data from pointer in step 1 while write is still on-going

 Multiple reads are allowed

Pointer to Record 0 VEE Record 0

VEE Record 1 VEE Record 1

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Why not have R_FlashRead() instead?

 User would call this function to read data

 Data would have to be copied every time

 No way to prevent user from directly accessing

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Virtual EEPROM for RL78

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RL78 – EEPROM Emulation Library

 Has similar features

 Uses ‘pools’

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RL78 – EEL Modes

 Has 3 execution modes

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Questions?

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 Devices in a smart society must efficiently use their available resources Eliminating the need for external components

when they can be incorporated inside the MCU is vital

‘Enabling The Smart Society’

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