宇宙飞船控制器状态机设计与实现.pdfVIP

第十三章例题

[例1]宇宙飞船控制器的状态机

modulestatemachine(launch_shuttle,land_shuttle,start_countdown,start_trip_meter,

clk,all_systems_go,just_launched,is_landed,cnt,abort_mission);

outputlaunch_shuttle,land_shuttle,start_countdown,start_trip_meter;

inputclk,just_launched,is_landed,abort_mission,all_systems_go;

input[3:0]cnt;

reglaunch_shuttle,land_shuttle,start_countdown,start_trip_meter;

//设置独热码状态的参数

parameterHOLD=5b00001,SEQUENCE=5b00010,LAUNCH=5b00100;

parameterON_MISSION=5b01000，LAND=5b10000;

reg[4:0]state;

always@(negedgeclkorposedgeabort_mission)

begin

//检查异步reset的值,即abort_mission的值

if(abort_mission)

{launch_shuttle,land_shuttle,start_trip_meter,start_countdown}=4b0000;

state=LAND;

else

begin

/*主状态机，状态变量state*/

case(state)

HOLD:if(all_systems_go)

begin

state=SEQUENCE;

start_countdown=1;

end

else

state=HOLD;

SEQUENCE:if(cnt==0)

state=LAUNCH;

else

state=SEQUENCE;

LAUNCH:

begin

state=ON_MISSION;