Examples of Instructions on DLX

To understand these tables we need to introduce notations of the description language.

A subscript is appended to the symbol <- whenever the length of the datum being tranferred might not be clear. Thus, <- n mean transfer an n -bit quantity.
A subscript is used to indicate selection of a bit from a field. Bits are labeled from the most-significant bit starting at 0. The subscript may be a single digit (e.g. Regs[R4] yields the sign bit of R4) or a subrange (e.g. Regs[R3] 24..31 yields the least-significant byte of R3).
The variable Mem, used as an array that stands for main memory, is indexed by a byte address and may transfer any number of bytes.
A superscript is used to replicate a fields (e.g. 0 24 yields a fiels of zeros of length 24 bits).
The symbol ## is used to concatenate two fields and may appear on either side of a data transfer.
 
Examples of arithmetic/logical instructions on DLX
Example instruction Instruction name Meaning
ADD R1, R2, R3 Add Regs[R1] <- Regs[R2]+Regs[R3]
ADDI R1, R2, #3 Add immediate Regs[R1] <- Regs[R2] + 3
LHI R1, #42 Load high immediate Regs[R1] <- 42##016
SLLI R1, R2, #5 Shift left logical immediate Regs[R1] <- Regs[R2] << 5
SLT R1, R2, R3 Set less than if (Regs[R2]<Regs[R3])
 Regs[R1] <- 1
else Regs[R1] <- 0


The load and store instructions in DLX
Example instruction Instruction name Meaning
LW R1,30(R2) Load word Regs[R1] <-32Mem[30+Regs[R2]]
LW R1,1000(R0) Load word Regs[R1] <-32Mem[1000+0] ; Register R0 always contains 0
LB R1,40(R3) Load byte Regs[R1] <-32(Mem[40+Regs[R3]]0)24##Mem[40+Regs[R3]]
LBU R1,40(R3) Load byte unsigned Regs[R1] <-32024 ## Mem[40+Regs[R3]]
LH R1,40(R3) Load half word Regs[R1] <-32(Mem[40+Regs[R3]]0)16 ## Mem[40+Regs[R3]] ## Mem[41+Regs[R3]]
LF F0,50(R3) Load float Regs[F0] <-32Mem[50+Regs[R3]]
LD FO,50(R2) Load double Regs[F0] ##Regs[F1]<-64Mem[50+Regs[R2]]
SW 500(R4),R3 Store word Mem[500+Regs[R4]] <-32Regs[R3]
SF 40(R3),F0 Store float Mem[40+Regs[R3]] <-32Regs[F0]
SD 40(Re),F0 Store double Mem[40+Regs[R3]] <-32Regs[F0];
Mem[44+Regs[R3]] <-32Regs[F1]
SH 502(R2),R3 Store half Mem[502+Regs[R2]] <-16Regs[R3]16..31
SB 41(R3),R2 Store byte Mem[41+Regs[R3]] <-8Regs[R2]24..31

Typical control-flow instructions in DLX
Example instruction Instruction name Meaning
J       name Jump PC<-name; ((PC+4)-225) <= name< ((PC+4)+225)
JAL name Jump and link R31<-PC+4;  PC<-name; ((PC+4)-225)<=name<((PC+4)+225)
JALR R2 Jump and link register Regs[R31]<-PC+4; PC , Regs[R2]
JR        R3 Jump register PC <- Regs[R3]
BEQZ R4, name Branch equal zero if (Regs[R4]==0) PC<-name;
((PC+4)-215)<=name<((PC+4)+215)
BNEZ R4, name Branch not equal zero if (Regs[R4]!=0) PC<-name;
((PC+4)-215)<=name<((PC+4)+215)