tests/extmod: Support esp32,mimxrt,stm32,samd ports in UART TX test.

Getting this test running on stm32- and mimxrt-based boards requires adding
a small delay after constructing the UART so that the initial idle frame
has time to be transmitted before the test starts.

Also, the timing margin needs to account for an additional 1-bit worth of
time on some MCUs.

Thanks to @robert-hh for the esp32, mimxrt and samd settings.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

tests/extmod/machine_uart_tx.py

@@ -9,20 +9,43 @@
 
 import time, sys
 
+initial_delay_ms = 0
+bit_margin = 0
+timing_margin_us = 100
+
 # Configure pins based on the target.
-if "rp2" in sys.platform:
+if "esp32" in sys.platform:
+    uart_id = 1
+    pins = {}
+    timing_margin_us = 400
+elif "mimxrt" in sys.platform:
+    uart_id = 1
+    pins = {}
+    initial_delay_ms = 20  # UART sends idle frame after init, so wait for that
+    bit_margin = 1
+elif "pyboard" in sys.platform:
+    uart_id = 4
+    pins = {}
+    initial_delay_ms = 50  # UART sends idle frame after init, so wait for that
+    bit_margin = 1  # first start-bit must wait to sync with the UART clock
+elif "rp2" in sys.platform:
     uart_id = 0
-    tx_pin = "GPIO0"
-    rx_pin = "GPIO1"
+    pins = {"tx": "GPIO0", "rx": "GPIO1"}
     timing_margin_us = 180
+elif "samd" in sys.platform:
+    uart_id = 2
+    pins = {"tx": "D1", "rx": "D0"}
+    timing_margin_us = 300
+    bit_margin = 1
 else:
     print("SKIP")
     raise SystemExit
 
 # Test that write+flush takes the expected amount of time to execute.
 for bits_per_s in (2400, 9600, 115200):
     text = "Hello World"
-    uart = UART(uart_id, bits_per_s, bits=8, parity=None, stop=1, tx=tx_pin, rx=rx_pin)
+    uart = UART(uart_id, bits_per_s, bits=8, parity=None, stop=1, **pins)
+    time.sleep_ms(initial_delay_ms)
 
     start_us = time.ticks_us()
     uart.write(text)
@@ -33,4 +56,5 @@
     bits_per_char = 10
     expect_us = (len(text)) * bits_per_char * 1_000_000 // bits_per_s
     delta_us = abs(duration_us - expect_us)
-    print(bits_per_s, delta_us <= timing_margin_us or delta_us)
+    margin_us = timing_margin_us + bit_margin * 1_000_000 // bits_per_s
+    print(bits_per_s, delta_us <= margin_us or delta_us)