Embedded System Design How Linux Boots on the SoCKit Board
Contents
1. C address Media Access Control address a 48 bit Ethernet address NFS Network File System a protocol for mounting a remote disk Used to enable the Linux root filesystem on the server to appear on the board POR Power On Reset PXE Preboot eXecution Environment a protocol that provides information to the board about which kernel to download etc Uses DHCP and TFTP QsPI Quad Serial Peripheral Interface a variant of the simple synchronous serial peripheral interface protocol that uses four data lines hence quad The interface between the HPs and an onboard flash chip sp Secure Digital a flash card format The SoCKit board accepts mini sp cards TFTP Trivial File Transfer Protocol an insecure very simple way to transfer files over the Internet e g the Linux kernel image Bibliography Boot the Arrow SoCKit from QSPI http www rocketboards org foswiki Documentation BootTheArrowSoCKit FromQSPI SoCKit User Manual http www terasic com tw cgi bin page archive p1l Language English amp CategoryNo 167 amp No 816 amp PartNo 42. CSEE 4840 Embedded System Design How Linux Boots on the SoCKit Board Stephen A Edwards Columbia University 2015 This explains how Linux boots over the network on the SoCKit boards in our lab It also explains how the server is configured Contents 1 Overview 2 2 The QSPI Flash Chip 3 2a Bisbee OSPI hood hb Seo eho e FSS SSSR HPAES ESS OS 3 23 Booting from the QSPI es eee ed eh oS OSE READ ERS 4 3 U Boot 5 Si Patching and Compiling se a sa eee RS a RE RSS 5 3 2 BOGE OCHINL dosana s paaa eaan a ae a a E a Sede 6 4 Network Configuration 7 44 Static Network Configuratii aia 4s a ee o aie e E a E a eh 7 ao Port Forwarding NAT e e s emoi sos ae Ok eK E AEN i aa 8 5 DHCP Server Configuration 9 6 TFTP Server Configuration 10 7 PXE Configuration 11 8 NES Server Configuration 12 Glossary 13 Bibliography 14 1 Overview The boot process proceeds as follows 1 The first stage bootloader loads from onboard serial flash resets the processor config ures the memory controller and loads the second stage bootloader 2 The second stage bootloader sets the board s Ethernet address uses DHCP to obtain the board s 1p address and the address of the TETP NFS server 3 The second stage bootloader uses TFTP to download pxelinux cfg default which contains paths to kernel images FPGA files and device tree files 4 The user selects one of these groups by typing on the console 5 The second stage bootloader uses TFTP to down
3. LOADADDR 0x8000 cd u boot socfpga for num in 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 do echo define BOARDNUM num gt include configs boardnum h make mrproper MAKEALL socfpga_cyclone5 mv u boot img u boot num img done This generates files of the form u boot o2 img which need to be flashed to the osr 3 2 Boot Script The initial U Boot environment for the first board is set to bootargs console ttySO 57600 ethaddr 1c 76 ca 48 40 01 loadaddr 0x3000000 pxefile_addr_r 0x3000000 kernel_addr_r 0x7fc0O fdt_addr_r 0x100 ramdisk_addr_r 0x2000000 fpga 0 fpgadatasize 6AEBDO updatebootargs setenv bootargs bootargs ip ipaddr serverip localcmd fpga load fpga ramdisk_addr_r fpgadatasize run updatebootargs bootm kernel_addr_r fdt_addr_r and the boot command is dhcp pxe get pxe boot The first three bytes of each board s Ethernet are Terasic s registered prefix the next two are the number of the class and the last byte indicates the board number the one thing that differs among boards in BCD 0X01 OXO9 OX10 OX19 OX20 When it gets control the second stage bootloader 1 Uses DHCP to get its 1p address and TFTP server address 2 Uses TFTP according to the PxE standard to fetch the pxelinux cfg default file which specifies the pathname for the kernel the rbf file taken from pxe s facility for the initial RaMdisk image ini
4. OSTROUTING o eth2 j MASQUERADE Nar port forwarding using the ufw package In etc default ufw DEFAULT_FORWARD_POLICY ACCEPT In etc ufw sysctl conf net ipv4 ip_forward 1 Add to etc ufw before rules right after the initial comments nat Table rules nat POSTROUTING ACCEPT 0 0 Forward traffic from eth1 through eth0 A POSTROUTING s 192 168 1 0 24 o ethO j MASQUERADE don t delete the COMMIT line or these nat table rules won t be processed COMMIT 5 DHCP Server Configuration Our U Boot setup queries DHCP to get various network parameters including the board s 1p address and the address of the TFTP server where it downloads the pxE configuration file Under CentOS install the dhcpd package Run pucp on only one of the interfaces by editing etc sysconfig dhcpd DHCPDARGS eth1 Under Ubuntu install the isc dhcp server package Run DHCP on only one of the interfaces by editing etc default isc dhcp server INTERFACES eth1 The main configuration file is etc dhcpd conf under CentOS etc dhcpd dhcpd conf under Ubuntu For the 192 168 1 network this defines the router as 192 168 1 1 the server DNS servers Columbia s and will automatically assign network addresses between 20 and 99 to devices that request them We assign fixed addresses to each SoCKit board based on its Mac address and tell each the address of the TFTP server subnet 192 168 1 0 netmask 255 255 255 0 option route
5. P For our purposes it amounts to a single configuration file accessible from TFTP as pxelinux cfg default in the export directory if TFTP is so configured The file consists of a list of labels each of which corresponds to a particular running environment kernel image FPGA configuration device tree blob and root directory Here is a representative example Note that prompt 1 default lab2 label lab2 menu label lab2 kernel 2014 _groups lab2 uImage initrd 2014 groups lab2 soc_system rbf append console ttyS0 57600 root dev nfs rw nfsroot 192 168 1 1 export 2014_groups lab2 root fdt 2014 groups lab2 socfpga dtb localboot 1 label lab3 menu label lab3 kernel 2014 groups lab3 uImage initrd 2014 _groups lab3 soc_system rbf append console ttyS0 57600 root dev nfs rw nfsroot 192 168 1 1 export 2014_groups lab3 root fdt 2014 groups lab3 socfpga dtb localboot 1 8 NES Server Configuration Nrs is an Internet protocol for remotely mounting filesystems It allows the SoCKit boards to store their root directories i e the entire filesystem on the server Under CentOS install the nfs utils and nfs utils lib packages and chkconfig nfs on service rpcbind start service nfs start Under Ubuntu install the nfs kernel server package and service nfs kernel server start The configuration file for NFs is etc exports We export the root filesystems to the SoCKit boards and allow the workstations to also mount the relevant directory
6. he front of the board control the source form which the HPs initially boots HPS Boot Source Selection BOOTSEL 2 0 Function 111 3 3V spi Flash Memory 101 3 3V sD MMc Flash Card 001 FPGA We want the HPs to be able to configure the FPGA with data downloaded from the server A tiny dipswitch on the back of the board SW6 SW6 1 SW6 5 sets MSEL which controls where the FPGA loads its configuration data FPGA Configuration Modes MSEL 4 0 Function gt 10000 Passive Serial from HPs fast POR 10001 Passive Serial from HPs standard POR 10010 Active Serial from onboard EPca flash fast POR 10011 Active Serial from onboard Epcaq flash standard POR 3 U Boot U Boot is a boot loader with excellent support for ARM processors as well as others Altera distributes a version with support for the Cyclone V on the SoCKit board 31 Patching and Compiling I modified two files in the U Boot source tree to enable pxE and configure the FPGA common cmd_pxe c Moved the call to label_localboot in the pxe command to run localcmd after loading files instead of before include configs socfpga_cyclone5 h Enabled PxE support by adding define directives and completely changed the initial variable environment to use PxE and configure the FPGA Compilation of the second stage bootloader images proceeds as follows opt altera 13 1 embedded embedded_command_shell sh export ARCH arm export CROSS_COMPILE arm none eabi export
7. load the kernel image the device tree and FPGA bitstream file programs the FGPA and passes control to the Linux kernel 6 The Linux kernel enumerates and initializes devices mounts the root directory with NFS then runs sbin init which runs the initialization scripts in etc init d eventually running a getty instance which prompts for a username and password 2 The QSPI Flash Chip We store the U Boot bootloader in the Qspi onboard flash chip and instruct the HPs to boot from it so each board does not need an sp card 2 1 Flashing the QSPI There are a few ways to flash the qsp1 but the easiest is to copy the two bootloader image files onto an sp card boot into U Boot e g from an sp card and halt the automatic booting process by pressing a key during the initial countdown This should give the U Boot command line At the U Boot command line verify the contents of the Far filesystem on the sp verify that you can access the qspi flash chip load the two bootloader files into memory then erase and flash the asp1 chip with the two files This is done as shown below This writes the 64K first stage bootloader to address o and the 256K second stage bootloader to address 0x60000 The first stage bootloader is the same for every board but we customize the second stage bootloader by giving each a unique Mac address 2 2 Booting from the QSPI We want the HPs to boot from onboard qspi flash memory Three BOOTSEL jumpers on t
8. rs 192 168 1 1 option subnet mask 255 255 255 0 option domain name servers 128 59 1 3 128 59 1 4 range 192 168 1 20 192 168 1 99 group SoCKit boards next server 192 168 1 1 TFTP server host board01 hardware ethernet 1c 76 ca 48 40 01 fixed address 192 168 1 101 host board02 hardware ethernet 1c 76 ca 48 40 02 fixed address 192 168 1 102 o CIE 6 TFTP Server Configuration TFTP as its name suggests is a very simple Internet file transfer protocol used mostly for system bootstrapping applications such as ours It is insecure e g no usernames or passwords so should only be run on protected networks and only has provisions for downloading and uploading files it cannot list directories for example Under CentOS you need the xinetd and tftp server packages under Ubuntu xinetd and tftpd Under CentOS sbin chkconfig level 345 xinetd on sbin chkconfig level 345 tftp on Under Ubuntu update rc d xinted enable Configure it with etc xinitd d tftp service tftp socket_type dgram protocol udp wait yes user nobody server usr sbin in tftpd server_args s export disable no bind 192 168 1 1 flags IPv4 This puts the root of what files it can serve at export runs it as the nobody user and binds it only to the interface associated with 192 168 1 1 7 PXE Configuration Unlike the other servies PXE is not a daemon by itself but is instead built on DHCP and TET
9. so files such as the FPGA configuration file can be updated Export root filesystems to the SoCKit boards export 2014_ groups 192 168 1 rw no_root_squash no_subtree_check Export to the workstations export 2014_ groups microl ilab columbia edu rw export 2014_ groups micro2 ilab columbia edu rw export 2014_groups micro3 ilab columbia edu rw nee it Cre Glossary BCD Binary Coded Decimal A way to represent decimal base 10 numbers in binary that uses four bits per decimal digit DHCP Dynamic Host Configuration Protocol used to send the 1p address and other network configuration details to the SoCKit board gt DNS Domain Name Service The Internet protocol that translates names like google com into 1p addresses like 192 168 1 5 EPCQ Erasable Programmable Configurable Quad a four bit wide serial flash device that can hold the FpGa s configuration bitstream Not used when we have the bootloader configure the FPGA with data from the server FAT File Allocation Table The ms pos filesystem typically used to format sp cards Flash Nonvolatile memory that can be reprogrammed slowly Used to hold the bootloader code FPGA Field Programmable Gate Array e g the main Cyclone V chip on the board HPs Hard Processor System the ARM processor and associated peripherals on the Cyclone V FPGA IP address Internet Protocol address a 32 bit address typically written in dotted decimal form e g 192 168 1 12 MA
10. trd and the device tree file pxE s fdt 3 Prints a menu of options PxE labels the user selects one 4 Fetches the kernel image the FPGA bitstream and the device tree blob using TFTP 5 Configures the FPGA using the just downloaded bitstream file 6 Adds information about the rp address of the board and the the nrs server assumed to be the same as the TFTP server to the Linux boot command line 7 Boots the Linux kernel informing it about the serial console its 1p adress the NFs server address and the address of the device tree blob 4 Network Configuration We place a server between a local network with all the SoCKit boards and the rest of the Internet Among other things it acts as a network address translator that allows the SoCKit boards to reach the Internet but not vice versa 192 168 1 1 ethi 128 59 The Internet 192 168 1 128 59 Server SoCKit board Workstation 4 1 Static Network Configuration Under CentOS etc sysconfig network scripts ifcfg eth1 DEVICE eth1 BOOTPROTO none HWADDR 00 04 23 9f 30 16 ONBOOT yes HOTPLUG no TYPE Ethernet NETMASK 255 255 255 0 IPADDR 192 168 1 1 Under Ubuntu etc network interfaces auto eth1 iface ethl inet static address 192 168 1 1 network 192 168 1 0 netmask 255 255 255 0 broadcast 192 168 1 255 gateway 192 168 1 1 4 2 Port Forwarding NAT Nar port forwarding out eth2 using iptables sbin iptables t nat A P
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