This document provides an overview of CMSIS (Cortex Microcontroller Software Interface Standard) and Cortex M bootup fundamentals. It discusses the following: - CMSIS modules like CMSIS-Core, CMSIS-SVD, CMSIS-Driver API that standardize interfaces for Cortex M microcontrollers. - Cortex M system memory map including code, SRAM, peripheral, and system control spaces. The system control space contains registers for clock control, NVIC, SysTick etc. - Cortex M bootup process which involves initializing the core, peripherals, copying code to RAM, and setting up the runtime environment. - Processor modes of handler and thread, and privilege

1. Cortex M Bootup & CMSIS - Part 1 / 3
Raahul Anand Raghavan, Lead Systems Architect,
Glyton Solutions
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2. Agenda
• Before We Proceed!
• Introduction to CMSIS
• CMSIS Modules
• Bootup Fundamentals
• ARM® Cortex M System Level Memory Map
• Processor Modes, Privilege level and Stacks
• Whats in Part 2 ?
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3. Before We Proceed!
• This is a 3 part presentation which would practically
introduce ARM® Cortex M boot up / system initialization &
CMSIS interface
• Involves Cortex M0 based EVM and a suitable IDE
• Official Documentation from ARM®, Silicon Labs will
override information provided here. Treat official TRM’s as
complete guides on Subject Matter
• ARM® Cortex® M trademark - ARM Ltd
• EFM®32, Silicon Labs SDK etc are registered trademarks
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4. Introduction to CMSIS (1 / 2)
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Cortex M processor
Firmware
Middleware
Application Code
Firmware Before CMSIS
No common specification across silicon
vendors using ARM® Cortex M IP
Firmware interface specification is
silicon vendor specific
Porting RTOS, peripheral code
complicated
Lengthy learning curve & Negative
Impact on Time to Market

5. Introduction to CMSIS (2 / 2)
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Cortex M processor
Middleware
Application Code
Firmware After CMSIS
Modular,Functionally mapped.Standardized
Interface Specification for various modules
defined by ARM®.
Port RTOS, peripheral device driver code
with more ease
Less learning curve & Reduced Time to
Market
CMSIS-Core CMSIS-SVD CMSIS-DAP
CMSIS-DSP
CMSIS-
RTOS API
CMSIS-
Driver API
Debugger
IDE

6. CMSIS Modules
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CMSIS-Core
CMSIS-SVD
CMSIS-DAP
CMSIS-RTOS API
CMSIS-Driver API
CMSIS-DSP
HAL(Systick,NVIC,SCB,MPU,FPU),system initialization,system
exception names,CPU specific intrinsic functions etc
Provides programmers view for memory mapped peripherals.
Maintained by Silicon Vendors
Standardized firmware for a debugger connecting to on chip
coresight debug access port
Standardized API’s RTOS interface
RTOS independent API’s connecting middleware stack to MCU
peripherals
Collection of DSP Libraries
CMSIS-PACK
Software package including all necessary headers,source files,
libraries,examples, flash programmers for a specific eval module

7. Bootup Fundamentals
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• What is Boot-up (or) system initialization ?
• Setting up the required environment on chip and associated peripherals, leading up to application code execution
• Initialize
• Core (Clock,NVIC, System timers, Exception Handlers etc…)
• Peripherals
• Copy code from NV (On Chip or On Board NAND / NOR / eMMC) to RAM or SRAM
• Setup C Runtime environment
• ……..
• How ?
• By programming various memory mapped registers which in turn control MCU using CMSIS core interfaces
• What system level information do we need to know ?
• System Memory Map (System Control Space,Systick timer, NVIC etc)
• System Instructions & CMSIS Core Interfaces
• Exceptions handlers
• ……..

8. Cortex M Core - System Memory Map (1 / 3)
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Code
(512MB)
0x00000000
0x1FFFFFFF
SRAM
(512MB)
0x20000000
0x3FFFFFFF
Peripheral
(512MB)
0x40000000
0x5FFFFFFF
RAM
(512MB)
0x60000000
0x7FFFFFFF
RAM
(512MB)
0x80000000
0x9FFFFFFF
Device
(512MB)
0xA0000000
0xBFFFFFFF
Device
(512MB)
0xC0000000
0xDFFFFFFF
System
(512MB)
0xE0000000
0xFFFFFFFF
Vendor_Sys
0xE0100000
0xFFFFFFFF
PPB
(1 MB)
0xE0000000
0xE00FFFFF
ROM Table
(4KB)
0xE00FFFFF
Reserved
ETM
(4 KB)
TPIU
(4 KB)
Reserved
System Control Space
(4 KB)
Reserved
FPB
(4 KB)
DWT
(4 KB)
ITM
(4 KB)
0xE0000000

9. Cortex M Core - System Memory Map (2 / 3)
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ROM Table
(4KB)
0xE00FFFFF
Reserved
ETM
(4 KB)
TPIU
(4 KB)
Reserved
System Control Space
(4 KB)
Reserved
FPB
(4 KB)
DWT
(4 KB)
ITM
(4 KB)
0xE0000000
µC-specific ID
Implementation
Defined
SW Triggered Interrupt
Debug
MPU
System Control Block
NVIC
SysTick
Auxiliary Control
0xE000E000
0xE000F000
CPACR and FP
CPUID
FSRs & FARs
SHCSR
SHPR3
SHPR2
SHPR1
CCR
SCR
AIRCR
VTOR
ICSR
CPUID

10. Cortex M Core - System Memory Map (3 / 3)
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CPACR and FP
CPUID
FSRs & FARs
SHCSR
SHPR3
SHPR2
SHPR1
CCR
SCR
AIRCR
VTOR
ICSR
CPUID
Coprocessor Access Control and FP registers
Reserved for other CPUID registers
Fault status and address registers
System Handler Control and State Register
System Handler Priority Register 3
System Handler Priority Register 2
System Handler Priority Register 1
Configuration and Control Register
System Control Register
Application Interrupt and Reset Control Register
Vector Table Offset Register
Interrupt Control and State Register
CPUID Base Register

11. Accessing Memory Mapped Control Registers
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• CMSIS Core Register Abstraction headers files
• Ex: core_cmx.h (X could be 0,3,4 etc based on which
Cortex M Core is used)
• CMSIS core Intrinsic function interface for accessing
and configuring System Control Space
• More on this in Part 2 when we take a look at a Cortex
M0 based EVM boot up

12. Processor Modes, Privilege & Stacks
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• Only two modes
• Handler Mode — Used to handle exceptions.
Main stack is used
• Thread Mode — Used to execute application
code. Main (or) Process Stack.Refer to the
table below
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• Privilege Levels
• Privileged — Access to all processor
resources and instructions
• Unprivileged — Restricted access to core
register read and write instructions
(MSR,MRS)
Mode Privilege Stack Pointer Usage Scenario
Handler Privileged Main Exception Handling. Also upon reset
Thread Privileged
Main Privileged Process execution using main/common stack
Process
Privileged process execution using individual process
specific stack
Thread Unprivileged
Main
Unprivileged process execution using main/common
stack
Process
Privileged process execution using individual process
specific stack

13. Whats in Part 2 ?
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• Typical Cortex M Boot up sequence
• Setting up EFM®32 starter kit with Silicon Labs SDK
• Set Break points & Investigate various stages during boot
up sequence
• Map CMSIS Core API’s with boot up stages identified
above
• Follow up in Part 3…