LC3 TRAP's Instructions -


this question that's giving me lot of trouble, need understand final exam in 2 weeks. don't know if it's wording, have no idea how arrive @ concrete answer. here's question:

"bob plans make changes mechanism of lc-3 trap instructions. has 2 ideas: make use of bit [8:11] of trap instructions. first instruction of trap routine stored @ address specified in trap instruction, rather starting address of trap routine. in new design, still wants implement many trap routines original lc-3 trap. calculate on average how many lines of instructions each trap routine have in new design."

i know trap has 3 fundamental trap vectors, x20, x25, , x23? "how many lines of instructions" mean?

is class using mc graw hill lc-3 simulator? because reading through text on trap command, bits [8:11] aren't sent mar load memory, they're dropped. bits [7:0] used because point location in trap vector table.

copyright mc graw hill

memory locations x0000 through x00ff, 256 in all, available contain starting addresses system calls specified corresponding trap vectors. region of memory called trap vector table.

the vector table using 6 of 256 available trap vectors, make 250 of own trap calls.

after trying "bob" trying following error "1024 can not represented 8 bit trap vector" , when try , manually fill in own trap call (ex. trap400 .fill xf400 ;which 1111 0100 0000 0000) won't run subroutine.

that being said, question can mean bob making his own version of lc-3 , increase amount of trap vectors can use. if that's case using bits [11:0] have 4,095 trap commands or 4,089 if not include original 6.

i hope helps.


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