mimxrt: Enable default devices for I2C, SPI and UART.

Since all boards are configured to have a I2C(0), SPI(0) and UART(1), these
can be set as default devices, allowing the instantiation of I2C(), SPI(),
UART() without an id argument.

Signed-off-by: robert-hh <robert@hammelrath.com>

docs/mimxrt/quickref.rst

@@ -122,10 +122,13 @@ See :ref:`machine.UART <machine.UART>`. ::
     uart1 = UART(1, baudrate=115200)
     uart1.write('hello')  # write 5 bytes
     uart1.read(5)         # read up to 5 bytes
+    uart1 = UART(baudrate=19200) # open UART 1 at 19200 baud
 
 The i.MXRT has up to eight hardware UARTs, but not every board exposes all
 TX and RX pins for users. For the assignment of Pins to UART signals,
-refer to the :ref:`UART pinout <mimxrt_uart_pinout>`.
+refer to the :ref:`UART pinout <mimxrt_uart_pinout>`. If the UART ID is
+omitted, UART(1) is selected. Then, the keyword
+option for baudrate must be used to change it from the default value.
 
 PWM (pulse width modulation)
 ----------------------------
@@ -305,12 +308,15 @@ rates (up to 30Mhz).  Hardware SPI is accessed via the
     cs_pin(0)
     spi.write('Hello World')
     cs_pin(1)
+    spi = SPI(baudrate=4_000_000)  # Use SPI(0) at a baudrate of 4 MHz
 
 For the assignment of Pins to SPI signals, refer to
 :ref:`Hardware SPI pinout <mimxrt_spi_pinout>`.
 The keyword option cs=n can be used to enable the cs pin 0 or 1 for an automatic cs signal. The
 default is cs=-1. Using cs=-1 the automatic cs signal is not created.
 In that case, cs has to be set by the script. Clearing that assignment requires a power cycle.
+If the SPI ID is omitted, SPI(0) is selected. Then, the keyword
+option for baudrate must be used to change it from the default value.
 
 Notes:
 
@@ -355,6 +361,10 @@ has the same methods as software SPI above::
 
     i2c = I2C(0, 400_000)
     i2c.writeto(0x76, b"Hello World")
+    i2c = I2C(freq=100_000)  # use I2C(0) at 100kHz
+
+If the I2C ID is omitted, I2C(0) is selected. Then, the keyword
+option for freq must be used to change the freq from the default value.
 
 I2S bus
 -------

ports/mimxrt/machine_i2c.c

@@ -34,6 +34,7 @@
 #include "fsl_iomuxc.h"
 #include "fsl_lpi2c.h"
 
+#define DEFAULT_I2C_ID          (0)
 #define DEFAULT_I2C_FREQ        (400000)
 #define DEFAULT_I2C_DRIVE       (6)
 #define DEFAULT_I2C_TIMEOUT     (50000)
@@ -91,7 +92,7 @@ static void machine_i2c_print(const mp_print_t *print, mp_obj_t self_in, mp_prin
 mp_obj_t machine_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
     enum { ARG_id, ARG_freq, ARG_drive, ARG_timeout};
     static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_id, MP_ARG_REQUIRED | MP_ARG_OBJ },
+        { MP_QSTR_id, MP_ARG_INT, {.u_int = DEFAULT_I2C_ID} },
         { MP_QSTR_freq, MP_ARG_INT, {.u_int = DEFAULT_I2C_FREQ} },
         { MP_QSTR_drive, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = DEFAULT_I2C_DRIVE} },
         { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = DEFAULT_I2C_TIMEOUT} },
@@ -102,7 +103,7 @@ mp_obj_t machine_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     mp_arg_parse_all_kw_array(n_args, n_kw, all_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
     // Get I2C bus.
-    int i2c_id = mp_obj_get_int(args[ARG_id].u_obj);
+    int i2c_id = args[ARG_id].u_int;
     if (i2c_id < 0 || i2c_id >= MICROPY_HW_I2C_NUM || i2c_index_table[i2c_id] == 0) {
         mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("I2C(%d) doesn't exist"), i2c_id);
     }

ports/mimxrt/machine_spi.c

@@ -37,6 +37,7 @@
 #include "fsl_lpspi.h"
 #include "fsl_lpspi_edma.h"
 
+#define DEFAULT_SPI_ID          (0)
 #define DEFAULT_SPI_BAUDRATE    (1000000)
 #define DEFAULT_SPI_POLARITY    (0)
 #define DEFAULT_SPI_PHASE       (0)
@@ -130,7 +131,7 @@ static void machine_spi_print(const mp_print_t *print, mp_obj_t self_in, mp_prin
 mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
     enum { ARG_id, ARG_baudrate, ARG_polarity, ARG_phase, ARG_bits, ARG_firstbit, ARG_gap_ns, ARG_drive, ARG_cs };
     static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_id,       MP_ARG_REQUIRED | MP_ARG_OBJ },
+        { MP_QSTR_id,       MP_ARG_INT, {.u_int = DEFAULT_SPI_ID} },
         { MP_QSTR_baudrate, MP_ARG_INT, {.u_int = DEFAULT_SPI_BAUDRATE} },
         { MP_QSTR_polarity, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = DEFAULT_SPI_POLARITY} },
         { MP_QSTR_phase,    MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = DEFAULT_SPI_PHASE} },
@@ -146,7 +147,7 @@ mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     mp_arg_parse_all_kw_array(n_args, n_kw, all_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
     // Get the SPI bus id.
-    int spi_id = mp_obj_get_int(args[ARG_id].u_obj);
+    int spi_id = args[ARG_id].u_int;
     if (spi_id < 0 || spi_id >= MP_ARRAY_SIZE(spi_index_table) || spi_index_table[spi_id] == 0) {
         mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("SPI(%d) doesn't exist"), spi_id);
     }

ports/mimxrt/machine_uart.c

@@ -37,6 +37,7 @@
 #include "modmachine.h"
 #include "pin.h"
 
+#define DEFAULT_UART_ID  (1)
 #define DEFAULT_UART_BAUDRATE (115200)
 #define DEFAULT_BUFFER_SIZE (256)
 #define MIN_BUFFER_SIZE  (32)
@@ -377,10 +378,17 @@ static void mp_machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args,
 }
 
 static mp_obj_t mp_machine_uart_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
-    mp_arg_check_num(n_args, n_kw, 1, MP_OBJ_FUN_ARGS_MAX, true);
+    mp_arg_check_num(n_args, n_kw, 0, MP_OBJ_FUN_ARGS_MAX, true);
 
     // Get UART bus.
-    int uart_id = mp_obj_get_int(args[0]);
+    int uart_id;
+    if (n_args > 0) {
+        uart_id = mp_obj_get_int(args[0]);
+        n_args--;
+        args++;
+    } else {
+        uart_id = DEFAULT_UART_ID;
+    }
     if (uart_id < 0 || uart_id > MICROPY_HW_UART_NUM || uart_index_table[uart_id] == 0) {
         mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("UART(%d) doesn't exist"), uart_id);
     }
@@ -409,7 +417,7 @@ static mp_obj_t mp_machine_uart_make_new(const mp_obj_type_t *type, size_t n_arg
     if (uart_present) {
         mp_map_t kw_args;
         mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
-        mp_machine_uart_init_helper(self, n_args - 1, args + 1, &kw_args);
+        mp_machine_uart_init_helper(self, n_args, args, &kw_args);
         return MP_OBJ_FROM_PTR(self);
     } else {
         return mp_const_none;