The kernel provides the function elv_next_request to obtain the first incomplete request on the queue, that function returns NULL when there are no requests to be processed. Note that elv_next_request does not remove the request from the queue. If you … Continue reading →

In block driver request function check whether request is valid or not as per filesystem request. void request(request_queue_t *queue); After validation ,it calls transfer function to perform the write or read operation. sbull_transfer(dev, req->sector, req->current_nr_sectors, req->buffer, rq_data_dir(req));

struct sbull_dev { int size; /* Device size in sectors */ u8 *data; /* The data array */ short users; /* How many users */ short media_change; /* Flag a media change? */ spinlock_t lock; /* For mutual exclusion */ … Continue reading →

struct gendisk (declared in <linux/genhd.h>) is the kernel’s representation of an indi- vidual disk device. In fact, the kernel also uses gendisk structures to represent parti- tions, but driver authors need not be aware of that. There are several fields … Continue reading →

After character devices and network devices, block devices are another important device type of any system ?Block Devices are used for the storage of application code and data, and user data, they are often critical to the overall performance of … Continue reading →

The IDT is stored in the idt_table table, which includes 256 entries. The 6-byte idt_descr variable specifies both the size of the IDT and its address, it is used only when the kernel initializes the idtr register with the lidt … Continue reading →

An Intel interrupt gate that cannot be accessed by a User Mode process (the gate’s DPL field is equal to 0). All Linux interrupt handlers are activated by means of interrupt gates, and all are restricted to Kernel Mode.

A program usually begins with a main() function, executes a bunch of instructions and terminates upon completion of those instructions. Kernel modules work a bit differently. A module always begin with either the init_module or the function you specify with … Continue reading →

When the kernel needs a feature that is not resident in the kernel, the kernel module daemon kmod ‘execs’ modprobe to load the module in. modprobe is passed a string in one of two forms: * A module name like … Continue reading →

If we need to refer to single bit of controller then syntax is sbit led p1^1; then change in led variable reflect on 1 pin of p1 port

All interrupt handlers perform the same four basic actions: 1. Save the IRQ value and the registers contents in the Kernel Mode stack. 2. Send an acknowledgment to the PIC that is servicing the IRQ line, thus allowing it to … Continue reading →

In 3d globe ,u need to calculate time slot using rpm of the machine.with this u can calculate which leds needs to be lighted up at that particular instant

A system table called Interrupt Descriptor Table (IDT) associates each interrupt or exception vector with the address of the corresponding interrupt or exception handler. The IDT must be properly initialized before the kernel enables interrupts. The IDT format is similar … Continue reading →

In DTMF we use 8770 ic which decode the dual-tone, multi-frequency send through u’r phone. After this u can program u’r IC to do specified works

Each hardware device controller capable of issuing interrupt requests has an output line designated as an IRQ (Interrupt ReQuest). All existing IRQ lines are connected to the input pins of a hardware circuit called the Interrupt Controller, which performs the … Continue reading →