UART

Introduction

The UART protocol could be used, for instance, to emit and receive RS232 / RS485 frames.

There is an example of an 8 bits frame, with no parity and one stop bit :

Bus definition

case class Uart() extends Bundle with IMasterSlave {
  val txd = Bool  // Used to emit frames
  val rxd = Bool  // Used to receive frames

  override def asMaster(): Unit = {
    out(txd)
    in(rxd)
  }
}

UartCtrl

An Uart controller is implemented in the library. This controller has the specificity to use a sampling window to read the rxd pin and then to using an majority vote to filter its value.

IO name	direction	type	Description
config	in	UartCtrlConfig	Used to set the clock divider/parity/stop/data length of the controller
write	slave	Stream[Bits]	Stream port used to request a frame transmission
read	master	Flow[Bits]	Flow port used to receive decoded frames
uart	master	Uart	Interface to the real world

The controller could be instantiated via an UartCtrlGenerics configuration object :

Attribute	type	Description
dataWidthMax	Int	Maximal number of bit inside a frame
clockDividerWidth	Int	Width of the internal clock divider
preSamplingSize	Int	Specify how many samplingTick are drop at the beginning of a UART baud
samplingSize	Int	Specify how many samplingTick are used to sample `rxd` values in the middle of the UART baud
postSamplingSize	Int	Specify how many samplingTick are drop at the end of a UART baud