stm32/uart: Add rxbuf keyword arg to UART constructor and init method.

As per the machine.UART documentation, this is used to set the length of
the RX buffer.  The legacy read_buf_len argument is retained for backwards
compatibility, with rxbuf overriding it if provided.

ports/stm32/uart.c

@@ -607,7 +607,7 @@ STATIC void pyb_uart_print(const mp_print_t *print, mp_obj_t self_in, mp_print_k
                 mp_print_str(print, "CTS");
             }
         }
-        mp_printf(print, ", timeout=%u, timeout_char=%u, read_buf_len=%u)",
+        mp_printf(print, ", timeout=%u, timeout_char=%u, rxbuf=%u)",
             self->timeout, self->timeout_char,
             self->read_buf_len == 0 ? 0 : self->read_buf_len - 1); // -1 to adjust for usable length of buffer
     }
@@ -634,12 +634,13 @@ STATIC mp_obj_t pyb_uart_init_helper(pyb_uart_obj_t *self, size_t n_args, const
         { MP_QSTR_flow, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = UART_HWCONTROL_NONE} },
         { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 1000} },
         { MP_QSTR_timeout_char, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0} },
-        { MP_QSTR_read_buf_len, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 64} },
+        { MP_QSTR_rxbuf, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
+        { MP_QSTR_read_buf_len, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 64} }, // legacy
     };
 
     // parse args
     struct {
-        mp_arg_val_t baudrate, bits, parity, stop, flow, timeout, timeout_char, read_buf_len;
+        mp_arg_val_t baudrate, bits, parity, stop, flow, timeout, timeout_char, rxbuf, read_buf_len;
     } args;
     mp_arg_parse_all(n_args, pos_args, kw_args,
         MP_ARRAY_SIZE(allowed_args), allowed_args, (mp_arg_val_t*)&args);
@@ -719,6 +720,10 @@ STATIC mp_obj_t pyb_uart_init_helper(pyb_uart_obj_t *self, size_t n_args, const
     }
     self->read_buf_head = 0;
     self->read_buf_tail = 0;
+    if (args.rxbuf.u_int >= 0) {
+        // rxbuf overrides legacy read_buf_len
+        args.read_buf_len.u_int = args.rxbuf.u_int;
+    }
     if (args.read_buf_len.u_int <= 0) {
         // no read buffer
         self->read_buf_len = 0;

tests/pyb/uart.py

@@ -30,3 +30,15 @@ print(uart.write(b'1'))
 print(uart.write(b'abcd'))
 print(uart.writechar(1))
 print(uart.read(100))
+
+# set rxbuf
+uart.init(9600, rxbuf=8)
+print(uart)
+uart.init(9600, rxbuf=0)
+print(uart)
+
+# set read_buf_len (legacy, use rxbuf instead)
+uart.init(9600, read_buf_len=4)
+print(uart)
+uart.init(9600, read_buf_len=0)
+print(uart)

tests/pyb/uart.py.exp

@@ -12,8 +12,8 @@ UART XB
 UART YA
 UART YB
 ValueError Z
-UART(1, baudrate=9600, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=3, read_buf_len=64)
-UART(1, baudrate=2400, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=7, read_buf_len=64)
+UART(1, baudrate=9600, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=3, rxbuf=64)
+UART(1, baudrate=2400, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=7, rxbuf=64)
 0
 3
 4
@@ -22,3 +22,7 @@ None
 4
 None
 None
+UART(1, baudrate=9600, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=3, rxbuf=8)
+UART(1, baudrate=9600, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=3, rxbuf=0)
+UART(1, baudrate=9600, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=3, rxbuf=4)
+UART(1, baudrate=9600, bits=8, parity=None, stop=1, flow=0, timeout=1000, timeout_char=3, rxbuf=0)