My Tech notes

The Advancement of technology had entered into nanometer age. search in google define:Blue-ray will get wiki pages here is summary of it. Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage medium designed to supersede the standard DVD format. Its main uses are for storing PlayStation 3 games, high-definition video, and data storage, with up to 50 GB per disc. This is quite impressive, The disc has the same physical dimensions as standard DVDs and CDs. Why Blu-ray disc stores 50GB on same size of DVD/CD? Well here is advancement of laser technology, thanks to Shuji Nakamura for his invention on blue laser, The name Blu-ray Disc derives from the blue-violet laser used to read the disc. While a standard DVD uses a 650 nanometre red laser, Blu-ray uses a shorter wavelength, a 405 nm blue-violet laser, and allows for almost six times more data storage than on a DVD. check out about Blu-ray Movies - Everything about Blu-ray movies and releases .at http://www.blu-ra...

Get HyperSCSI for SAN - Storage Area Network SCSI (Small Computer Systems Interface) family of protocols. HyperSCSI can allow one to connect to and use SCSI and SCSI-based devices (like IDE, USB, Fibre Channel) over a network as if it was directly attached locally. Why HyperSCSI over iSCSI? The main advantage of HSCSI compared to iSCSI is especially a lower network load as well as an end system (server and client) load. TCP/IP SAN performance is still not good enough without hardware acceleration FC-based SANs cannot do Storage Wide-Area Networks Fully functional software implementation of both client and server so HSCSI can be used for a solution built on commonly available hardware, no expensive and specialized hardware is needed. Therefore, HSCSI can be used for building small and cheap SANs. HSCSI main disadvantage is this protocol has no official standard like iSCSI nd so it is unsupported in any way by manufacturers developing hardware data storage solutions. Two modes of oper...

Use of bootloader, in SoC design. SoC in simple terms is collection of required blocks, like USB, MAC, PCI, surrounded to the CPU (generally RISC CPU, ARM). As a part of SoC development each hardware block is validated for its functionality. Validation is done register level. Example if we want to test functionality provided by MAC block in our SoC, then these functionality are validated by writing test cases in bootloader (u-boot-1.1.6). Bootloader will create an environment for the test cases. The test cases are added as commands for each block with different subtests for each block to touch the corner conditions. To start with U-boot provides generic block test cases, like I2C and many more are getting added day by day. Format of bootloader commands int do_hello (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]) { printf("Hello World\n"); } U_BOOT_CMD( hello, 5, 0, do_hello, " hello - Prints hello world\n", ...

How to participate in the Linux kernel community? check out A GUIDE TO THE KERNEL DEVELOPMENT PROCESS Jonathan Corbet has written a very interesting article on "how to participate in the Linux kernel community" Section 1 is the executive summary. Section 2 introduces the development process, the kernel release cycle, and the mechanics of the merge window. Section 3 covers early-stage project planning, with an emphasis on involving the development community as soon as possible. Section 4 is about the coding process; several pitfalls which have been encountered by other developers are discussed. Section 5 talks about the process of posting patches for review. Section 6 covers what happens after posting patches; the job is far from done at that point. Section 7 introduces managing patches with git and reviewing patches posted by others. Section 8 concludes the document with pointers to sources for more information on kernel development. Please take a look at the complete documen...

Things to keep in mind for kernel programming If you want to hack Linux kernel and do some programs, before you start keep some points in mind First and very basic point to make you feel relax with linux kernel , as, kernel is nothing but a program as like other programs, which includes memory management, process scheduling, system management and all you need to work in. 1. In kernel space you do not have leisure of GLIBc library, ie you can not use printf also you have printk in kernel space. 2. Limited stack - you have limited stack space in kernel so do not make unnecessary variables declared, as tomorrow you may be going to add some new features. In user space you have almost unlimited stack so you will be little worried about how many variables you are using. 3. In kernel space no memory protection is there, as in user space if some memory corruption occurs kernel will trap and send signal. In kernel space there is no-one to trap memory corruption, it is like you are directly ...

Invoking user mode application from kernel modules, yes its possible with help of CALL_USERMODEHELPER . With the following kernel API, we can invoke user mode application from Kernel modules/threads. int call_usermodehelper (char * path, char ** argv, char ** envp, int wait); path: pathname for the application. argv: null-terminated argument list. envp: null-terminated environment list. wait: wait for application to finish and return status. Example: Kernel Module: #include #include char name[]="user_program"; static int init_function(void) { int ret; char *argv[] = {name, "hello", "world", NULL }; static char *envp[] = { "HOME=/", "TERM=linux", "PATH=/sbin:/usr/sbin:/bin:/usr/bin", NULL }; printk("We r in init_function\n"); ret= call_usermodehelper(name, argv, envp, 1); if ( ret #include int...

Kernel Memory Layout on ARM Linux Russell King November 17, 2005 (2.6.15) This document describes the virtual memory layout which the Linux kernel uses for ARM processors. It indicates which regions are free for platforms to use, and which are used by generic code. The ARM CPU is capable of addressing a maximum of 4GB virtual memory space, and this must be shared between user space processes, the kernel, and hardware devices. As the ARM architecture matures, it becomes necessary to reserve certain regions of VM space for use for new facilities; therefore this document may reserve more VM space over time. Start End Use -------------------------------------------------------------------------- ffff8000 ffffffff copy_user_page / clear_user_page use. For SA11xx and Xscale, this is used to setup a minicache mapping. ffff1000 ffff7fff Reserved. Platforms must not use this address range. ffff0000 ffff0fff CPU vector page. The CPU vectors are mapped here if the CPU supports...

Help ksymoops out mkdir /var/log/ksymoops Every time a module is loaded /proc/ksymsand /proc/modules is copied there. -k /var/log/ksymoops/ .ksyms -l /var/log/ksymoops/ .modules dbg() macro #if !defined(CONFIG_FOO_MODULE) #define MY_NAME "foo_driver" #else #define MY_NAME THIS_MODULE->name #endif #define dbg(fmt, arg...) do { if (debug) printk(KERN_DEBUG "%s: "__FUNCTION__": " fmt "\n" , MY_NAME , ## arg); } while (0) static int debug; MODULE_PARM(debug, "i"); Using dbg() dbg ("Added slot %d to the list", slot->physical_number); shows up as: hotplug_pci: pci_hp_register: Added slot 2 to the list dbg (""); shows up as: hotplug_pci: pci_hp_register: Other printk() macros #define err(fmt, arg...) printk(KERN_ERR "%s: " fmt "\n" , MY_NAME , ## arg) #define info(fmt, arg...) printk(KERN_INFO "%s: " fmt "\n"...