C from FW

1. 淺談-從FW看C語言
feathertw@gmail.com
翔翔

2. Issue?
● What's the different between SOC and MCU?
● What’s a 32bit architecture mean?
● What’s ARM and ST relationship?
● What is stack point, link register, program counter in Cortex-M?
● How to program C code with considering BUS architeture?
● Assembly is really neccessary in Cortex-M when init C code environment?
● How an OS use CPU mode to protect task without MMU?
● Choose Cortex-M4 is good for running DSP code?

3. C Program
語法
平台編譯
C規格、資料結構…
CPU、Periperal、OS…Compiler、Linker、Debuger…

4. SOC & MCU
ARM Cortex-A Series
ARM Cortex-M Series

5. ARM & ST
● CPU
○ Cortex
A,R,M
● Debug
● ToolChain
● Software
Ecosystem
● (BUS)
● Package
○ LQFP144
○ BGA
● Memory
○ Flash
○ Ram
● Peripheral
○ Timer
○ Uart

6. IC Industry Chain

7. Cortex-M4F
● 32bit、3stage pipeline
● FPU、SIMD、MAC instruction
● CMSIS
○ Core info
○ Vendor Peripheral Mapping
○ OS interface
○ Library
○ Function
■ __disable_irq()
■ __ROR()
■ __WFI()

8. BUS-AMBA

9. Register

10. NVIC
● Nested, Vector Table
● Priority
○ vendor implement
○ group priority、subpriority
○ low number means high priority
● Exception stack frame
○ R0、R1、R2、R3、R12、LR、PC、xPSR
● Exception return
○ Return to Handler mode 0XFFFFFFF1
○ Return to Thread mode and using MSP 0xFFFFFFF9
○ Return to Thread mode and using PSP 0xFFFFFFFD
● Vector Table Offset Register (VTOR)

11. Thumb-2 ISA
● 16bit、32bit instruction(16bit with low register)
○ .N .W
○ MOVW、MOVT
○ CLZ
● Instruction with postfix ‘S’
● Access memory
○ LDR R2, [R3] ;R2 = mem32[R3]
○ LDR R2, [R3, #4] ;R2 = mem32[R3 + 4]
○ LDR R2, [R3,#4]! ;R2 = mem32[R3 + 4] ; R3 = R3 + 4
○ LDR R2, [R3], #4 ;R2 = mem32[R3] ; R3 = R3 + 4
● IF-THEN Instruction
○ if else in 4 instruction

12. RTOS
● Systick
● Processor mode
○ Thread mode、Handler mode
○ Unprivileged、Privileged
○ MSP、PSP
○ Control register
○ SVC #
● MPU

13. Toolchain
.c .s .o .elf .bin
gcc as ld objcopy
● Toolchain
○ cross-compiler
○ gcc、as、ld、objcopy、objdump、gdb

14. Compile
● Section
○ CODE
○ DATA
○ BSS
● Linker
● C Programming Initial
● AAPCS
● Const issue
MEMORY
{
FLASH (rx) : ORIGIN = 0x00000000,
LENGTH = 0x00040000
RAM (rwx) : ORIGIN = 0x01000000,
LENGTH = 0x00040000
}
SECTIONS
{
.text :
{
_stext = . ;
*(vectors)
*(.text)
_etext = . ;
} > FLASH
.data : AT(_etext)
{
_sdata = . ;
*(.rodata*)
*(.data)
_edata = . ;
} > RAM
data_size = _edata - _sdata ;
.bss :
{
_sbss = . ;
*(.bss)
_ebss = . ;
} > RAM
bss_size = _ebss - _sbss ;
}

15. FPU
● gcc parameter
○ -mfloat-abi=soft
○ -mfloat-abi=softfp
○ -mfloat-abi=hard
● Lazy stacking feature
● Floating-point register with context switch

16. Q&A

17. Do you really know how do program run?
#include <stdio.h>
#include <unistd.h>
int main()
{
int i;
for(i=0; i<3; i++)
{
fork();
printf("-");
}
return 0;
}
$ gcc fork.c -o fork && ./fork | wc -c
Explain output number!

18. THX