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package Uart where
import FIFOF
import GetPut
-- | The state of the TX side of the UART.
data TxState
= -- | The UART is not currently sending anything. May transition to
-- 'Start b' when ready to send 'b'.
Idle
| -- | The UART is about to send the start bit. 'Start b' transitions to
-- 'Data b 7' by sending the start bit.
Start (Bit 8)
| -- | The UART is about to send a data bit. 'Data b n' transitions to
-- 'Data (b >> 1) (n - 1)' by sending a data bit. 'Data b 0' transitions to
-- 'Idle' by sending the last data bit. Being in the 'Idle' state for a
-- clock transmits the stop bit.
Data (Bit 8) (Bit 3)
deriving (Bits)
-- | The TX side of the UART.
interface TxUart =
-- | The TX pin.
pin :: Bit 1
-- | Writes a byte to the UART's transmit buffer.
send :: Put (Bit 8)
mkTxUart :: Integer -> Module TxUart
mkTxUart bufferSize = module
fifo :: FIFOF (Bit 8) <- mkSizedFIFOF bufferSize
state :: Reg TxState <- mkReg Idle
pin :: Reg (Bit 1) <- mkReg 1
rules
"uart_tx_idle": when Idle <- state, not fifo.notEmpty ==> do
pin := 1
"uart_tx_idle_to_start": when Idle <- state, fifo.notEmpty ==> do
pin := 1
b <- (toGet fifo).get
state := Start b
"uart_tx_start": when Start b <- state ==> do
pin := 0
state := Data b 7
"uart_tx_data": when Data b n <- state ==> do
pin := b[0:0]
if n == 0 then
state := Idle
else
state := Data (b >> 1) (n - 1)
interface TxUart
pin = pin
send = toPut fifo
-- | The state of the RX side of the UART.
data RxState
= -- | The initial state of the UART, and the state after receiving the stop
-- bit. May transition to 'Data 0 0' when the start bit is received.
Idle
| -- | In the 'Data _ n' state, the UART has received the start bit and 'n'
-- data bits, and is about to receive more data bits. 'Data _ n'
-- transitions to 'Data _ (n + 1)' by receiving a data bit. 'Data b 7'
-- transitions to 'Stop' by receving the last data bit.
Data (Bit 8) (Bit 3)
| -- | In the 'Stop' state, the UART has received the start and data bits,
-- and is waiting for the stop bit (which is ignored). Transitions to
-- 'Idle'.
Stop (Bit 8)
deriving (Bits, FShow)
mkRxUart :: Wire (Bit 1) -> Integer -> Module (Get (Bit 8))
mkRxUart rx bufferSize = module
fifo :: FIFOF (Bit 8) <- mkGSizedFIFOF True False bufferSize
state :: Reg RxState <- mkReg Idle
rules
"uart_rx_idle_to_start": when Idle <- state, rx == 0 ==> do
state := Data 0 0
"uart_rx_data_to_data": when Data bits n <- state, n < 7 ==> do
state := Data (rx ++ bits[7:1]) (n + 1)
"uart_rx_data_to_stop": when Data bits 7 <- state ==> do
state := Stop (rx ++ bits[7:1])
"uart_rx_stop_to_idle": when Stop bits <- state, rx == 1 ==> do
fifo.enq bits
state := Idle
return (toGet fifo)
-- | An 8n1 UART.
interface Uart =
-- | The TX pin.
tx :: Bit 1
-- | Reads a byte from the UART's receive buffer.
recv :: Get (Bit 8)
-- | Writes a byte to the UART's transmit buffer.
send :: Put (Bit 8)
mkUart :: Wire (Bit 1) -> Module Uart
mkUart rx = module
recv <- mkRxUart rx 8
uart_tx <- mkTxUart 8
interface Uart
tx = uart_tx.pin
recv = recv
send = uart_tx.send
-- vim: set ft=haskell :
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