tests/extmod: Update I2S rate test to work on mimxrt.

Tested on Teensy 4.0.

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

tests/extmod/machine_i2s_rate.py

@@ -13,18 +13,24 @@
     i2s_id = 2
     sck_pin = Pin("Y6")
     ws_pin = Pin("Y5")
-    sd_pin = Pin("Y8")
+    sd_tx_pin = sd_rx_pin = Pin("Y8")
 elif "rp2" in sys.platform:
     i2s_id = 1
     sck_pin = Pin(0)
     ws_pin = Pin(1)
-    sd_pin = Pin(2)
+    sd_tx_pin = sd_rx_pin = Pin(2)
+elif "mimxrt" in sys.platform:
+    i2s_id = 1
+    sck_pin = Pin(26)
+    ws_pin = Pin(27)
+    sd_tx_pin = Pin(7)
+    sd_rx_pin = Pin(8)
 
 TEST_BYTES = b"01234567"
 RATE = 11025  # frames/sec
 
 
-def test(mode, bits_per_sample, frame_format):
+def test(mode, sd_pin, bits_per_sample, frame_format):
     i2s = I2S(
         i2s_id,
         sck=sck_pin,
@@ -70,11 +76,11 @@ def test(mode, bits_per_sample, frame_format):
     print(mode_str, bits_per_sample, channels, abs(dt - 500) <= 4)
 
 
-test(I2S.TX, 16, I2S.MONO)
-test(I2S.TX, 16, I2S.STEREO)
-test(I2S.TX, 32, I2S.MONO)
-test(I2S.TX, 32, I2S.STEREO)
-test(I2S.RX, 16, I2S.MONO)
-test(I2S.RX, 16, I2S.STEREO)
-test(I2S.RX, 32, I2S.MONO)
-test(I2S.RX, 32, I2S.STEREO)
+test(I2S.TX, sd_tx_pin, 16, I2S.MONO)
+test(I2S.TX, sd_tx_pin, 16, I2S.STEREO)
+test(I2S.TX, sd_tx_pin, 32, I2S.MONO)
+test(I2S.TX, sd_tx_pin, 32, I2S.STEREO)
+test(I2S.RX, sd_rx_pin, 16, I2S.MONO)
+test(I2S.RX, sd_rx_pin, 16, I2S.STEREO)
+test(I2S.RX, sd_rx_pin, 32, I2S.MONO)
+test(I2S.RX, sd_rx_pin, 32, I2S.STEREO)