#include <logic.h>
Data Fields | |
| LC3_WORD | addr |
| LC3_WORD | bits |
| opcode_t | opcode |
| int | DR |
| int | SR1 |
| int | SR2 |
| int | bit5 |
| int | bit11 |
| LC3_WORD | trapvect8 |
| LC3_WORD | imm5 |
| LC3_WORD | offset6 |
| LC3_WORD | PCoffset9 |
| LC3_WORD | PCoffset11 |
| LC3_WORD | SR1OUT |
| LC3_WORD | SR2MUX [2] |
| LC3_WORD | SR2MUXval |
| LC3_WORD | ADDR1MUX [2] |
| LC3_WORD | ADDR2MUX [4] |
This structure holds all the fields that occur in an instruction. Conceptually, all of these fields are computed in parallel in the combinational logic of the LC3 and the control logic selects the values to use depending on the actual instruction. In hardware, there is "no" cost to computing things you might not use. In the implementation, you may choose to precompute all the fields, or simply get values from the instruction itself as they are needed. This structure is used as the parameter for logic_fetch_instruction(), logic_decode_instruction(), and logic_execute_instruction(), ... .
| LC3_WORD inst_fields::addr |
address of the instruction
| LC3_WORD inst_fields::ADDR1MUX[2] |
the two inputs of ADDR2MUX. One value is a result of adding the BaseR and the offest. The other contains the incremented PC.
| LC3_WORD inst_fields::ADDR2MUX[4] |
Four inputs of ADDR2MUX. There is a 0 and three different sign extended values.
| int inst_fields::bit11 |
distinguishes JSR/JSRR
| int inst_fields::bit5 |
distinguishes immediate from register
| LC3_WORD inst_fields::bits |
16 bit instruction
| int inst_fields::DR |
destination register
| LC3_WORD inst_fields::imm5 |
immediate value
| LC3_WORD inst_fields::offset6 |
a register offset
| opcode_t inst_fields::opcode |
opcode of instruction
| LC3_WORD inst_fields::PCoffset11 |
offset from program counter
| LC3_WORD inst_fields::PCoffset9 |
offset from program counter
| int inst_fields::SR1 |
source register 1
| LC3_WORD inst_fields::SR1OUT |
value of SR1
| int inst_fields::SR2 |
source register 2
| LC3_WORD inst_fields::SR2MUX[2] |
the two inputs of SR2MUX. The value of bit5
selects the input to use
| LC3_WORD inst_fields::SR2MUXval |
value of SR2MUX
| LC3_WORD inst_fields::trapvect8 |
value for TRAP
1.8.3.1