hardware.h File Reference

defines interface to code simulating hardware (do not modify) More...

#include "lc3.h"
#include "logic.h"

Go to the source code of this file.

Macros
#define	HARDWARE_VAR   extern

Functions
void	hardware_reset (void)
void	hardware_load_MAR (void)
void	hardware_load_MDR (void)
void	hardware_gate_MDR (void)
void	hardware_gate_PC (void)
void	hardware_set_PC (LC3_WORD addr)
void	hardware_load_IR (void)
LC3_WORD	hardware_get_IR (void)
void	hardware_load_REG (int regNum)
LC3_WORD	hardware_get_REG (int regNum)
void	hardware_memory_enable (int rw)
void	hardware_set_mode (int mode)
int	hardware_get_CC (void)
void	hardware_set_CC (int val)
int	hardware_step (instruction_t *inst)

Variables
HARDWARE_VAR LC3_WORD *	lc3_BUS

Detailed Description

This defines the interface to the code simulating the hardware contained in hardware.c. There are a variety of routines corresponding to actions the control logic of the LC3 can perform. For example, it can gate various values onto the bus and transfer values to registers from the bus. It is expected that the student will encapsulate many of these routines to give a cleaner interface to the hardware. This code will be in logic.c. With the exception of the bus, all hardware data structures are hidden behind accessor functions.

Not all of the interface mirrors the LC3 hardware. The differences were designed to simplify the code.

Author

Fritz Sieker

Macro Definition Documentation

#define HARDWARE_VAR   extern

This controls whether variable is extern or not

Function Documentation

void hardware_gate_MDR

(

void

)

The value of the memory data register (MDR) is put "on" the bus.

void hardware_gate_PC

(

void

)

The value of the program counter (PC) is put "on" the bus.

int hardware_get_CC

(

void

)

Return the current value of the condition code.

LC3_WORD hardware_get_IR

(

void

)

Return the current value of the instruction register (IR).

LC3_WORD hardware_get_REG

(

int

regNum

)

Return the value of a register (0-7).

Parameters

regNum

- register to get value from

Returns

- value contained in designated registerget value from register R0-R7

void hardware_load_IR

(

void

)

The instruction register (IR) is loaded from the bus.

void hardware_load_MAR

(

void

)

The memory address register (MAR) is loaded from the bus.

void hardware_load_MDR

(

void

)

The memory data register (MDR) is loaded from the bus.

void hardware_load_REG

(

int

regNum

)

Copy the value "on" the LC3 bus into the designated register (0-7).

Parameters

regNum

- register to load

void hardware_memory_enable

(

int

rw

)

This is the low level memory access function. It controls whether a read or write is performed. Is assumes that the MAR and possibly the MDR have been set appropriately by calls to other functions.

Parameters

rw	- if non zero, a write is performed by trasfering the contents of the MDR to memory the address contained in the MAR. If it is 0, a read is performed and the contents of memory at the address contained in the MAR are copied to the MDR.

void hardware_reset

(

void

)

Reset all the hardware variables in the machine to a known state.

void hardware_set_CC

(

int

val

)

Set the condition code

Parameters

val	- new value for condition code

void hardware_set_mode

(

int

mode

)

Toggle between user and system mode. For future use.

Parameters

mode	- 0 is system mode, 1 is user mode

void hardware_set_PC

(

LC3_WORD

addr

)

The program counter (PC) is set to the parameter.

Parameters

addr	- new value for the PC

int hardware_step

(

instruction_t *

inst

)

This is the basis for doing single stepping durring debugging. It encapsulates the basic instruction cycle by making calls to three external routines, normally written by students as part of the simulator assignment. The routines are:

1. logic_fetch_instruction()
2. logic_decode_instruction()
3. logic_execute_instruction()

Parameters

inst	- storage for info of the instruction

Returns

0 on success, non-zero on failure

Variable Documentation

HARDWARE_VAR LC3_WORD* lc3_BUS

The LC3 bus is modeled as a pointer. Reading from the bus (dereferencing the pointer) is getting the value from whatever source is currently "driving" the bus. Similarly, writing on the bus invloves setting the pointer value. The bus is a global that can be accessed outside of this code.