tb: uart_rx: Export putchar

This function is useful for other testbenches. Export it.

Signed-off-by: Sean Anderson <seanga2@gmail.com>

tb/uart_rx.py

@@ -17,6 +17,11 @@ def as_bits(c):
         yield c & 1
         c >>= 1
 
+async def putchar(rx, c):
+    for bit in (0, *as_bits(c), 1):
+        rx.value = bit
+        await Timer(BIT_STEPS)
+
 @cocotb.test(timeout_time=1, timeout_unit='ms')
 async def test_rx(uart):
     uart.clk.value = BinaryValue('Z')
@@ -30,11 +35,6 @@ async def test_rx(uart):
     await cocotb.start(Clock(uart.clk, 8, units='ns').start())
     await FallingEdge(uart.clk)
 
-    async def putchar(c):
-        for bit in (0, *as_bits(c), 1):
-            uart.rx.value = bit
-            await Timer(BIT_STEPS)
-
     msg = b"Hell\0"
     signals = {
         'clk': uart.clk,
@@ -45,7 +45,7 @@ async def test_rx(uart):
 
     await cocotb.start(recv_packet(signals, msg))
     for c in msg:
-        await putchar(c)
+        await putchar(uart.rx, c)
 
     overflows = 0
     frame_errors = 0
@@ -69,8 +69,8 @@ async def test_rx(uart):
     assert frame_errors == 1
 
     uart.ready.value = 0
-    await putchar(0xFF)
-    await putchar(0)
+    await putchar(uart.rx, 0xFF)
+    await putchar(uart.rx, 0)
 
     assert overflows == 1