Assignment 5, due Feb. 25

On every assignment, write your name and the course number legibly. Exceptions will be by advance arrangement unless there is what insurance companies call "an act of God" (something outside your control). Homework must be turned in on paper, either in class or in the teaching assistant's mailbox. Never push late work under someone's door!

1. Background: IBM's modelk 3330 disk system was the defining disk technology of the early 1970s. Each disk pack had 404 cylinders (of which only 400 were typically used) and 20 surfaces (IBM used one surface for formatting information, other vendors used all 20 surfaces) and 13,030 bytes per track (frequently arranged as 24 sectors of 512 bytes each, wasting a few bytes in the process). So, for the purpose of this assignment, consider a 3330 as 400 cylinders of 20 surfaces of 24 sectors of 512 bytes. This gives 98.3 megabytes per disk pack.

   A problem: Write a C routine linearize(int linear, struct diskad * da) to translate linearized disk addresses of the form you would get from lseek() when applied to the raw disk device. The disk address parameter points to a structure with fields called cylinder, track (within cylinder), sector (within track), and byte (within sector). (1 point)

2. Background: Assume that you have a disk interface with the following control registers:
   • cylinder
   • surface
   • sector
   • command -- storing the command read, write or seek initiates an operation.
   • status -- contains a ready bit.

   The disk is one of many devices attached to a DMA controller with the following control registers:

   • count -- the number of bytes to tranfer to or from RAM
   • address -- the address of a buffer in RAM
   • command -- storing the command read or write initiates an operation
   • status -- contains a ready bit

   With multiple disks attached to one DMA channel, it is essential to tell both the controller and the disk interface to move the data in the same direction, and it is essential that only one disk attempt to transfer data at a time.

   a) Outline the code for a stupid version of disk_IO( struct diskad * da, char * buf, int command) that will perform one disk operation on the disk device. It should work correctly in a single-threaded system under the assumption that other devices (including other disks) are driven by similar routines. (1 point)

   b) Now, assume that each device can request an interrupt when it is done, and assume that disk interrupts are handled by a different interrupt handler than DMA interrupts. In support of disk interrupts, you have a disk request queue, but you also have to deal with the relationship between the disk and DMA interrupt routines. This might be mediated by an additional queue or queues. Design the communication pattern between the user-side routine that enqueues disk requests, the disk interrupt handler and the DMA interrupt handler. A sensible answer will probably involve a diagram showing how the queue or queues relate to the software components, a description of what goes in each queue, and a textual description of how the different routines relate to each other. (1 point)