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2 Laboratory Exercise #6 Obviously, other hardware/software interactions exist in our system, but Figure 1 focuses on that which you will provide. Also notice the existence of the kernel-space/user-space boundary. The kernel module represents the character device driver executing in kernel space, while the user application represents the code executing in user space, reading and writing to the device file, ‘/dev/multiplier’. The device file is not a standard file in the sense that it does not reside on a disk, rather it provides an interface for user applications to interact with the kernel. User Application /dev/multiplier user space kernel space kernel module multiplication peripheral software hardware Figure 1: Hardware/Software System Diagram Procedure 1. Compile a kernel module that reads and writes to the multiplication peripheral and prints the results to the kernel message buffer. (a) Create a lab6 directory and copy the ‘modules’ directory from your lab5 directory to your lab6 directory. 2 ECEN 449
Laboratory Exercise #6 3 (b) Navigate to the ‘modules’ directory and ensure the ‘Makefile’ points to the ‘linux-2.6.35.7’ kernel directory. (c) Create a new kernel module source file called ‘multiply.c’. (d) Copy the following skeleton code into ‘multiply.c’: # i n c l u d e / ∗ Needed by a l l modules ∗ / # i n c l u d e / ∗ Needed f o r KERN ∗ and p r i n t k ∗ / # i n c l u d e / ∗ Needed f o r i n i t and e x i t macros ∗ / # i n c l u d e / ∗ Needed f o r IO r e a d s and w r i t e s ∗ / # i n c l u d e ” x p a r a m e t e r s . h ” / ∗ needed f o r p h y s i c a l a d d r e s s o f m u l t i p l i e r ∗ / / ∗ from x p a r a m e t e r s . h ∗ / # d e f i n e PHY ADDR XPAR MULTIPLIER 0 BASEADDR ; / / p h y s i c a l a d d r e s s o f m u l t i p l i e r / ∗ s i z e o f p h y s i c a l a d d r e s s range f o r m u l t i p l y ∗ / # d e f i n e MEMSIZE XPAR MULTIPLIER 0 HIGHADDR − XPAR MULTIPLIER 0 BASEADDR+1; unsigned v i r t a d d r ; / / v i r t u a l a d d r e s s p o i n t i n g t o m u l t i p l i e r / ∗ T h i s f u n c t i o n i s run upon module load . T h i s i s where you s e t u p data s t r u c t u r e s and r e s e r v e r e s o u r c e s used by t h e module . ∗ / s t a t i c i n t i n i t m y i n i t ( void ) { / ∗ Linux k e r n e l ’ s v e r s i o n o f p r i n t f ∗ / p r i n t k ( KERN INFO ” Mapping v i r t u a l a d d r e s s . . . \ n ” ) ; / ∗ map v i r t u a l a d d r e s s t o m u l t i p l i e r p h y s i c a l a d d r e s s ∗ / / / use ioremap / ∗ w r i t e 7 t o r e g i s t e r 0 ∗ / p r i n t k ( KERN INFO ” W r i t i n g a 7 t o r e g i s t e r 0\n ” ) ; i o w r i t e 3 2 ( 7 , v i r t a d d r + 0 ) ; / / base a d d r e s s + o f f s e t / ∗ W r i t e 2 t o r e g i s t e r 1 ∗ / p r i n t k ( KERN INFO ” W r i t i n g a 2 t o r e g i s t e r 1\n ” ) ; / / use i o w r i t e 3 2 p r i n t k ( ” Read %d from r e g i s t e r 0\n ” , i o r e a d 3 2 ( v i r t a d d r + 0 ) ) ; p r i n t k ( ” Read %d from r e g i s t e r 1\n ” , \\ use i o r e a d 3 2 ) ; p r i n t k ( ” Read %d from r e g i s t e r 2\n ” , i o r e a d 3 2 ( v i r t a d d r + 8 ) ) ; / / A non 0 r e t u r n means i n i t m o d u l e f a i l e d ; module can ’ t be loaded . return 0 ; } / ∗ T h i s f u n c t i o n i s run j u s t p r i o r t o t h e module ’ s removal from t h e s y s t e m . You s h o u l d r e l e a s e ALL r e s o u r c e s used by your module h ere ( o t h e r w i s e be p r e p a r e d f o r a r e b o o t ) . ∗ / s t a t i c void e x i t m y e x i t ( void ) ECEN 449 3
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Page 5 and 6: Laboratory Exercise #6 5 • Use th
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