## 举例(Example)

### 一、外部断言(External assertions)

这是一个简单计数器和其对应形式化验证的例子：

```Scala
import spinal.core._

//Here is our DUT
class LimitedCounter extends Component{
  //The value register will always be between [2:10]
  val value = Reg(UInt(4 bits)) init(2)
  when(value < 10){
    value := value + 1
  }
}

object LimitedCounterFormal extends App {
  // import utilities to run the formal verification, but also some utilities to describe formal stuff
  import spinal.core.formal._

  // Here we run a formal verification which will explore the state space up to 15 cycles to find an assertion failure
  FormalConfig.withBMC(15).doVerify(new Component {
    // Instanciate our LimitedCounter DUT as a FormalDut, which ensure that all the outputs of the dut are:
    // - directly and indirectly driven (no latch / no floating wire)
    // - allows the current toplevel to read every signal across the hierarchy
    val dut = FormalDut(new LimitedCounter())

    // Ensure that the state space start with a proper reset
    assumeInitial(ClockDomain.current.isResetActive)

    // Check a few things
    assert(dut.value >= 2)
    assert(dut.value <= 10)
  })
}

Internal assertions

If you want you can embed formal statements directly into the DUT:

class LimitedCounterEmbedded extends Component{
  val value = Reg(UInt(4 bits)) init(2)
  when(value < 10){
    value := value + 1
  }

  // That code block will not be in the SpinalVerilog netlist by default. (would need to enable SpinalConfig().includeFormal. ...
  GenerationFlags.formal {
    assert(value >= 2)
    assert(value <= 10)
  }
}

object LimitedCounterEmbeddedFormal extends App {
  import spinal.core.formal._

  FormalConfig.withBMC(15).doVerify(new Component {
    val dut = FormalDut(new LimitedCounterEmbedded())
    assumeInitial(ClockDomain.current.isResetActive)
  })
}
```

### 二、内部断言(Internal assertions)

如果你愿意你也可以把形式化语句直接包含在DUT中：

```Scala
class LimitedCounterEmbedded extends Component{
  val value = Reg(UInt(4 bits)) init(2)
  when(value < 10){
    value := value + 1
  }

  // That code block will not be in the SpinalVerilog netlist by default. (would need to enable SpinalConfig().includeFormal. ...
  GenerationFlags.formal {
    assert(value >= 2)
    assert(value <= 10)
  }
}

object LimitedCounterEmbeddedFormal extends App {
  import spinal.core.formal._

  FormalConfig.withBMC(15).doVerify(new Component {
    val dut = FormalDut(new LimitedCounterEmbedded())
    assumeInitial(ClockDomain.current.isResetActive)
  })
}
```

### 三、外部激励(External stimulus)

如果你的DUT有输入, 你需要从testbench中驱动他们。所有的一般硬件语句都可以实现它, 但是你也可以用形式化*anyseq*,*qnyconst*, *allseq*, *allconst*语句：

```Scala
class LimitedCounterInc extends Component{
  //Only increment the value when the inc input is set
  val inc = in Bool()
  val value = Reg(UInt(4 bits)) init(2)
  when(inc && value < 10){
    value := value + 1
  }
}

object LimitedCounterIncFormal extends App {
  import spinal.core.formal._

  FormalConfig.withBMC(15).doVerify(new Component {
    val dut = FormalDut(new LimitedCounterInc())
    assumeInitial(ClockDomain.current.isResetActive)
    assert(dut.value >= 2)
    assert(dut.value <= 10)

    // Drive dut.inc with random values
    anyseq(dut.inc)
  })
}
```

### 四、更多的断言/传递(More assertions/past)

例如我们可以检查值是否计数自增(如果没到10):

```Scala
FormalConfig.withBMC(15).doVerify(new Component {
  val dut = FormalDut(new LimitedCounter())
  assumeInitial(ClockDomain.current.isResetActive)

  // Check that the value is incrementing.
  // hasPast is used to ensure that the past(dut.value) had at least one sampling out of reset
  when(pastValid() && past(dut.value) =/= 10){
    assert(dut.value === past(dut.value) + 1)
  }
})
```

### 五、假设存储内容(Assuming memory content)

本例中我们希望防止`1`出现在内存中：

```Scala
class DutWithRam extends Component{
  val ram = Mem.fill(4)(UInt(8 bits))
  val write = slave(ram.writePort)
  val read = slave(ram.readAsyncPort)
}

object FormalRam extends App {
  import spinal.core.formal._

  FormalConfig.withBMC(15).doVerify(new Component {
    val dut = FormalDut(new DutWithRam())
    assumeInitial(ClockDomain.current.isResetActive)

    // assume that no word in the ram has the value 1
    for(i <- 0 until dut.ram.wordCount){
      assumeInitial(dut.ram(i) =/= 1)
    }

    // Allow the write anything but value 1 in the ram
    anyseq(dut.write)
    clockDomain.withoutReset(){ //As the memory write can occur during reset, we need to ensure the assume apply there too
      assume(dut.write.data =/= 1)
    }

    // Check that no word in the ram is set to 1
    anyseq(dut.read.address)
    assert(dut.read.data =/= 1)
  })
}
```