Answer to:Joseph Salisbury (jsalisbury) Firstly I want to say thanks a lot! Before I test the latest upstream kernel, I want to give more information about this problem 1) I was reading a web page: PC Repair and Maintenance: In-depth Look at Power Supply, that it was reading By Scott Mueller Feb 28, 2003 (http://www.informit.com/articles/article.aspx?p=31105) 2) In the page 2, I found the following paragraph that describes the problem: If you find that a system consistently fails to boot up properly the first time you turn on the switch, but that it subsequently boots up if you press the reset or Ctrl+Alt+Delete warm boot command, you likely have a problem with the Power_Good timing. You should install a new, higher-quality power supply and see whether that solves the problem. 3) The unique difference is that I need to push reset button case not Ctrl+Alt+delete because keyboard is death 4) I changed the power supply for another with 650 W output 5) But the problem continues: startup+reset to keep the computer running 6) I was reading carefully the following paragraphs: "The Power_Good Signal In addition to supplying electrical power to run the system, the power supply also ensures that the system does not run unless the power supplied is sufficient to operate the system properly. In other words, the power supply actually prevents the computer from starting up or operating until all the power supply voltages are within the proper ranges.
The power supply completes internal checks and tests before allowing the system to start. If the tests are successful, the power supply sends a special signal to the motherboard, called Power_Good. This signal must be continuously present for the system to run. Therefore, when the AC voltage dips and the power supply cannot maintain outputs within regulation tolerance, the Power_Good signal is withdrawn (goes low) and forces the system to reset. The system will not restart until the Power_Good signal returns. The Power_Good signal (sometimes called Power_OK or PWR_OK) is a +5v (nominal) active high signal (with variation from +2.4v through +6.0v generally being considered acceptable) that is supplied to the motherboard when the power supply has passed its internal self tests and the output voltages have stabilized. This normally takes place anywhere from 100ms to 500ms (0.1–0.5 seconds) after you turn on the power supply switch. The power supply then sends the Power_Good signal to the motherboard, where the processor timer chip that controls the reset line to the processor receives it. In the absence of Power_Good, the timer chip holds the reset line on the processor, which prevents the system from running under bad or unstable power conditions. When the timer chip receives the Power_Good signal, it releases the reset, and the processor begins executing whatever code is at address FFFF:0000 (usually the ROM BIOS). If the power supply cannot maintain proper outputs (such as when a brownout occurs), the Power_Good signal is withdrawn, and the processor is automatically reset. When the power output returns to its proper levels, the power supply regenerates the Power_Good signal and the system again begins operation (as if you had just powered on). By withdrawing Power_Good before the output voltages fall out of regulation, the system never sees the bad power because it is stopped quickly (reset) rather than being allowed to operate using unstable or improper power levels, which can cause memory parity errors and other problems." 7) My motherboard is a GIGABYTE P35-DS3L and pin 8 of the main power connector receives Power Good signal 8) When power supply is ON, the following occurs: the main task performed by SMPS, is to inform about the good power supply. As I told if the voltage is more/ or is less, in both the conditions a computer cannot work. As soon as you supply power to the computer, the SMPS checks the voltage level's its providing to the motherboard. If the power signal level is perfect, then SMPS will send a POWER GOOD signal to the motherboard timer.On receiving this POWER GOOD signal from SMPS, the motherboard timer will stop sending reset signal to the CPU. Which means the power level is good and the computer can boot. 9) Bootstrapping: Something has to be programmed by default, so that the CPU knows where to search for instructions. This is an address location in the ROM. This address location is almost always constant in X86 based computers. The address location is FFFF:0000h. This address location is the last region of the ROM. It only contains one instruction. The instruction is to jump to another memory address location. This JUMP command, will tell the location of the BIOS program in the ROM. This is how the computer will come to know where the BIOS program is located. 9) The Role of BIOS in booting process: The word booting comes from another word called bootstrapping. The computer knows how to bring itself up, when you press the start button, because of the instructions that are fed to a program called as BIOS. BIOS stands for Basic Input Output System. The most important use of BIOS during the booting process is POST. POST stands for Power on Self Test. Its a series of tests conducted by the bios, which confirms the proper functioning of different hardware components attached to the computer. POST is very important thing to have before the Operating system is loaded. Just imagine if you have a faulty hard drive or faulty memory, sometimes these things can cause data loss. POST checks and confirms the integrity of the following hardware components. Timer IC's DMA controllers CPU Video ROM A full POST check will confirm the integrity of the following devices as well. Motherboard Keyboard Printer port Hard Drive etc If you are doing a warm start (which means you did a reset of a running machine, most of the times reset button is the small one near the power button on the CPU), a full POST check will not be conducted by the BIOS. However if you are doing a Cold Start, which means you have applied the power now, it will conduct a full POST. BIOS determines whether its a cold or warm start, by looking at a flag in a predefined memory location. Once the POST completes, the BIOS will inform you about any problems it found with the help of beep codes (through system speaker). Different number of beep codes have different meaning. Once the POST check is completed successfully, BIOS will look CMOS settings to know what is the boot order. Boot order is nothing but a user defined order which tells where to look for the operating system. The order will be something like the below. CD ROM HARD DISK (In my computer this is the first, an SSD disk) USB Floppy DISK The above shown order means that the BIOS will look at CD ROM first to check whether an OS can be loaded from there, if it does not find a bootable disk in the CD ROM, it will look check whether a bootable OS is there in the hard disk, then USB and then Floppy disk. Let's assume that you don’t have a bootable CD in your CD ROM drive, then the BIOS will turn to HARD disk. 10) MBR and GRUB: Now as you don't have any bootable CD in your CD ROM Drive, the bios will look at the second device from the boot order settings. The second device is your Hard Disk. BIOS is programmed to look at a permanent location on the hard disk to complete its task. This location is called a Boot sector. This is nothing but the first sector of your hard disk. This area is sometimes called as MBR (Master Boot Record). This is the location that contains the program that will help our computer to load the operating system. As soon as bios finds a valid MBR, it will load the entire content of MBR to RAM, and then further execution is done by the content of MBR. This first sector of the hard disk is only of 512 bytes. Yeah its too small an area for an entire boot loader program to fit in. Hence most of the operating system store only the first stage of their boot loader program in here. Only the first 440 bytes from the total of 512 bytes is used by the first stage boot loader, the remaining part is used to store partition table information. As the title of this article says "Linux Booting process", we will be having grub stage one in the first 440 bytes of the MBR. I would suggest to read the below artcle to understand grub and its details. First stage grub Partition table information Error messages Magic Number The fourth point is a Magic Number of 2 bytes. This magic number serves as a method of verification for the MBR. This 2 byte magic number will contain values that will be something like AA55. A different magic number indicates a corrupted MBR or invalid MBR. The primary job of the stage 1 bootloader is to load the second stage boot loader. The second stage boot loader is the stage 2 grub, that actually does the job of loading the kernel and other initrd image files (we will come to that part in some time). GRUB (Grand Unified Boot Loader) is the combined name given to different stages of grub. Now there is a little surprise that am going to reveal. There are not two stages of grub. But there are three stages of grub in total. I will explain you the reason behind this. The three stages are mentioned below. GRUB Stage 1 GRUB Stage 1.5 Grub Stage 2 Now from where does this stage 1.5 came. The hard disk sectors are counted form 0 to the last sector. As explained previously the first sector (sector 0) contains the GRUB stage 1. Normally partititons will not start before sector 63. So partitions will start form sector number 63. Hence we have sectors form 1-63 free. This space is used for storing GRUB stage 1.5. This free space between MBR and the beginning of the partitions is called as MBR GAP. Now you might think what is the requirement of an additional stage in grub. If you are a linux guy, you might have already configured grub configuration file. If you remember the configuration, it contains the kernel file location and name, its partition. Now how will the grub access those kernel files without the file system drivers? Grub Stage 1.5 located in the MBR GAP (sector 1 to 63 before the beginning of the first partition) basically contains the drivers for reading file systems. So grub stage 1 will load grub stage 1.5 to the RAM, and will pass the control to it. Now grub stage 1.5 will load the file system drivers and once the file system drivers are loaded, it can now access /boot/grub/grub.conf file which contains other details about kernel path and initrd path etc. Now this is the point where you are presented with a beautiful TUI (Terminal user interface), where you can select your operating system kernal and press enter to boot it. 11) Loading The kernel Image: Similar to GRUB, kernel is also loaded in stages. A linux kernel is responsible for handling Process management, Memory Management, Users, Inter process communication etc. I must say kernel is never used by a user. What the kernel does is to maintain a good environment for programs to run. Yeah we use kernel thrugh different programs. Kernel is a compressed image file. The location of this compressed kernel image is specified in the grub 2 configuration file. Its basically an executable bzImage file. Now you need to have a lot of drivers and modules to access underlying hardware and other stuff. For example, if you have RAID configured on your / partition how will you mount it without knowing the programs, or think how will you include a kernal module or how to remove a kernel module. All these things required different set of programs and code. Including all these codes inside the kernel will make it a larger file image. But our kernel image file needs to be smaller, that's the reason its compressed image file. So most of these drivers and tools along with a small similar root file system feel is given by initrd. Initrd is sometimes called as initial root file system. This is used by the kernel before the real root file system is mounted. Initrd is available in the form of an image similar to the kernel image file. Let's see what's the content of this initrd image file. You can find the initrd image file and the kernel image file in the /boot directory. Loading and unloading of kernel modules is done with the help of programs like insmod, and rmmod present in the initrd image. Now as the kernel is loaded into the memory, the execution begins by checking the processor family and architecture. The kernel conducts a lot of hard ware specific operations and the first user space program it executes is /sbin/init. As this is the first program executed by the kernel, it has got a process id number of 1. The process id number 1 for init was not kept intentionally, but it was due to the fact that it is the first process executed by the kernel. Now as soon as the kernel executes the init process, it will look at the /etc/inittab configuration file to see the default run level. There are different run level's in linux. Run-Level Usage 0 System Halt/Shut Down 1 Single User Mode 2 Multiuser Mode Without Networking 3 Full Multiuser Mode 4 Unused 5 GUI/X11 6 Reboot The /etc/inittab file contains the default run level like the one shown below. Now that means, we have a run level 3 as the default run level. Once this is identified, then run level specific programs are started by the kernel. This is the reason you have the following directories. The folders rc0.d, rc1.d, rc2.d etc contains run level specific programs that will be executed depending upon the default run level you have in your inittab configuration file. Once the kernel has started all programs in your desired run level directory. You will get a login screen to log inside your booted system. THEN WHAT IS HAPPENING? Why computer works very well with warm start and it fails at cold start? -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1637031 Title: In cold startup there is dark/blank screen To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1637031/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
