The World Leader in High Performance Signal Processing Solutions Das U-Boot: Blackfin Guts

Agenda Background Boot ROM U-Boot Beyond

Terms Loader Program that loads another, more complex, program Boot ROM The Blackfin on-chip ROM Bootloader / Bootstrap Loader Program that boots the “first program” such as the Linux kernel Bare Metal Stand alone program that runs directly on the processor No operating system

Das U-Boot The "Universal Bootloader" is open source firmware Started in October of 1999 by Dan Malek, supported by Wolfgang Denk (Denx Engineering) as of July 2000 Free Software - full source code under GPL Production quality code base Used as default boot loader by several board vendors Portable across processors and easy to port and to debug Many supported architectures: ARM, Blackfin, m68k, Microblaze, MIPS, NIOS, PowerPC, SuperH, x86, and more More than 260 boards supported by public source tree ~20 Blackfin boards

Boot ROM Power on Check BMODE pins Check OTP (if available) Setup selected boot source Load and process LDR found at boot source Load & execute init block Load blocks (code & data) Initialize filled blocks Pass execution off to LDR U-Boot is a standard LDR Boot ROM boot modes tested every release: Parallel Flash (bypass & LDR) SPI Serial Flash UART NAND

U-Boot LDR Layout Example U-Boot LDR for BF548-EZKIT Block 1 0x : 0xAD6D5006 0xFFA x x ( 16bit-dma-from-16bit ignore first ) Block 2 0x : 0xADAB0806 0xFFA x xDEADBEEF ( 16bit-dma-from-16bit init ) Block 3 0x : 0xAD x03F x00001E4C 0xDEADBEEF ( 16bit-dma-from-16bit ) Block 4 0x00001FF0: 0xAD x x xBAADF00D ( 16bit-dma-from-16bit ignore ) Block 5 0x : 0xAD x03F81E4C 0x xDEADBEEF ( 16bit-dma-from-16bit ) Block 6 0x : 0xADFE0006 0xFFA x xDEADBEEF ( 16bit-dma-from-16bit ) Block 7 0x : 0xAD x03FB20A4 0x0002D340 0x ( 16bit-dma-from-16bit fill final ) Block 2 – initialize block (“initcode”) Block 3/5 – code (.text/.data sections) Block 4 – embedded U-Boot environment Block 6 – L1 code (.l1.text) Block 7 – uninitialized data (.bss sections)

LDR initcode block Enable self refresh if external memory is enabled Suspend to RAM Loading another U-Boot in external memory (debugging / testing) Program clocks Use bfrom_SysControl() if available Otherwise do standard PLL reprogram sequence SIC_IWR, PLL_LOCKCNT, VR_CTL, PLL_DIV, PLL_CTL, SIC_IWR Program memory controller Disable self refresh if needed Check for Suspend to RAM resumption Program EBIU Asynchronous Memory Interface Set EVT1 to U-Boot entry point

Suspend to RAM Handled in LDR init block Check hibernate state in VR_CTL (if supported) Look for magic at address 0x xDEADBEEF Load resume address from 0x Load stack address from 0x Jump to hibernation resume point Linux restores itself from hibernate Restore on-chip memory from external memory Restore peripheral state Etc...

U-Boot Initialization Setup stack pointer Program SYSCFG Enable cycles Enable nested interrupts Initialize C runtime ABI Zero out loop / circular buffer / etc... registers Zero out BSS if not done by Boot ROM Lower execution to EVT15 Enable nested interrupts Setup exceptions, CPLBs, and cache Initialize CEC Initialize environment from its storage Boot up main program based on environment settings Linux kernel Bare metal application

U-Boot hardware use No interrupts are used No exceptions are used Except for CPLB miss to allow caching All CPLB misses are handled dynamically – no hard coded lists per processor that fall out of date or need board tweaking Only peripherals that are explicitly needed are initialized If booting from parallel flash, then initialize it If booting over network, then initialize MAC If booting over IDE, then initialize ATAPI Etc... Everything runs in poll mode No interrupts! Everything runs serially in a single thread

Booting user program Most common behavior is to boot the Linux kernel U-Boot works with “bootable U-Boot images” “uImage” is often the short name Contains flat binary image of program Includes CRC checking Arbitrary load & entry addresses Includes compression (gzip, bzip, lzma) Select boot source Flash: parallel, SPI, NAND, … Mass Storage: CF, USB, IDE, SATA, MMC, SD, … Dynamic: Ethernet, Wireless, Serial, … Load uImage over source Check CRC Decompress Jump to entry point

Booting user program (cont) U-Boot and program need not be in same storage Boot ROM boots U-Boot out of parallel flash, but U-Boot boots Linux off of SD card Linux and root file system need not be in same storage U-Boot boots Linux off of SD card, but Linux uses root file system in NAND flash Every file system format you can think of is supported FAT 12 / 16 / 32 JFFS / JFFS2 YAFFS / YAFFS2 ISO9660 (CDROM) Bad blocks with NAND Behavior is all controlled dynamically through U-Boot console

Board porting made easy Porting to your own board is trivial Lines of specific C code (including comments / whitespace) BF518F-EZBRD – 219 lines BF526-EZBRD – 284 lines BF527-EZKIT – 217 lines BF537-MINOTAUR – 244 lines BF537-SRV1 – 244 lines BF538F-EZKIT – 153 lines CM-BF561 – 125 lines Board specific code self contained include/configs/.h – configuration settings boards/ / – all board code Drivers provided for all major peripherals Customers encouraged to merge with our public tree Automatically updated to latest versions and compile tested

Debugging All debug options are configurable Completely disable for production if you wish “Early Serial Output” Get status messages over UART at every step (including initcode) Verbose CPU crash messages Automatic decoding of core registers SEQSTAT – hwerror & excause IPEND – pending interrupts Automatic trace buffer Decode the hardware trace buffer source / destination Automatic symbol resolution All addresses are decoded to symbol names + offsets Signal JTAG automatically upon crash

Questions ?