CircuitPython

Source code browser

Note: This site will be taken down by the end of the year

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
/*
 * This file is part of the Micro Python project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2013, 2014 Damien P. George
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <stdio.h>
#include <string.h>
#include <stdarg.h>

#include "py/ioctl.h"
#include "py/nlr.h"
#include "py/runtime.h"
#include "py/stream.h"
#include "py/mperrno.h"
#include "py/mphal.h"
#include "uart.h"
#include "irq.h"

//TODO: Add UART7/8 support for MCU_SERIES_F7

/// \moduleref pyb
/// \class UART - duplex serial communication bus
///
/// UART implements the standard UART/USART duplex serial communications protocol.  At
/// the physical level it consists of 2 lines: RX and TX.  The unit of communication
/// is a character (not to be confused with a string character) which can be 8 or 9
/// bits wide.
///
/// UART objects can be created and initialised using:
///
///     from pyb import UART
///
///     uart = UART(1, 9600)                         # init with given baudrate
///     uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters
///
/// Bits can be 8 or 9.  Parity can be None, 0 (even) or 1 (odd).  Stop can be 1 or 2.
///
/// A UART object acts like a stream object and reading and writing is done
/// using the standard stream methods:
///
///     uart.read(10)       # read 10 characters, returns a bytes object
///     uart.readall()      # read all available characters
///     uart.readline()     # read a line
///     uart.readinto(buf)  # read and store into the given buffer
///     uart.write('abc')   # write the 3 characters
///
/// Individual characters can be read/written using:
///
///     uart.readchar()     # read 1 character and returns it as an integer
///     uart.writechar(42)  # write 1 character
///
/// To check if there is anything to be read, use:
///
///     uart.any()               # returns True if any characters waiting

#define CHAR_WIDTH_8BIT (0)
#define CHAR_WIDTH_9BIT (1)

struct _pyb_uart_obj_t {
    mp_obj_base_t base;
    UART_HandleTypeDef uart;            // this is 17 words big
    IRQn_Type irqn;
    pyb_uart_t uart_id : 8;
    bool is_enabled : 1;
    byte char_width;                    // 0 for 7,8 bit chars, 1 for 9 bit chars
    uint16_t char_mask;                 // 0x7f for 7 bit, 0xff for 8 bit, 0x1ff for 9 bit
    uint16_t timeout;                   // timeout waiting for first char
    uint16_t timeout_char;              // timeout waiting between chars
    uint16_t read_buf_len;              // len in chars; buf can hold len-1 chars
    volatile uint16_t read_buf_head;    // indexes first empty slot
    uint16_t read_buf_tail;             // indexes first full slot (not full if equals head)
    byte *read_buf;                     // byte or uint16_t, depending on char size
};

STATIC mp_obj_t pyb_uart_deinit(mp_obj_t self_in);

void uart_init0(void) {
    for (int i = 0; i < MP_ARRAY_SIZE(MP_STATE_PORT(pyb_uart_obj_all)); i++) {
        MP_STATE_PORT(pyb_uart_obj_all)[i] = NULL;
    }
}

// unregister all interrupt sources
void uart_deinit(void) {
    for (int i = 0; i < MP_ARRAY_SIZE(MP_STATE_PORT(pyb_uart_obj_all)); i++) {
        pyb_uart_obj_t *uart_obj = MP_STATE_PORT(pyb_uart_obj_all)[i];
        if (uart_obj != NULL) {
            pyb_uart_deinit(uart_obj);
        }
    }
}

// assumes Init parameters have been set up correctly
STATIC bool uart_init2(pyb_uart_obj_t *uart_obj) {
    USART_TypeDef *UARTx;
    IRQn_Type irqn;
    uint32_t GPIO_Pin, GPIO_Pin2 = 0;
    uint8_t GPIO_AF_UARTx = 0;
    GPIO_TypeDef* GPIO_Port = NULL;
    GPIO_TypeDef* GPIO_Port2 = NULL;

    switch (uart_obj->uart_id) {
        #if defined(MICROPY_HW_UART1_PORT) && defined(MICROPY_HW_UART1_PINS)
        // USART1 is on PA9/PA10 (CK on PA8), PB6/PB7
        case PYB_UART_1:
            UARTx = USART1;
            irqn = USART1_IRQn;
            GPIO_AF_UARTx = GPIO_AF7_USART1;
            GPIO_Port = MICROPY_HW_UART1_PORT;
            GPIO_Pin = MICROPY_HW_UART1_PINS;
            __USART1_CLK_ENABLE();
            break;
        #endif

        #if defined(MICROPY_HW_UART1_TX_PORT) && \
            defined(MICROPY_HW_UART1_TX_PIN) && \
            defined(MICROPY_HW_UART1_RX_PORT) && \
            defined(MICROPY_HW_UART1_RX_PIN)
        case PYB_UART_1:
            UARTx = USART1;
            irqn = USART1_IRQn;
            GPIO_AF_UARTx = GPIO_AF7_USART1;
            GPIO_Port  = MICROPY_HW_UART1_TX_PORT;
            GPIO_Pin   = MICROPY_HW_UART1_TX_PIN;
            GPIO_Port2 = MICROPY_HW_UART1_RX_PORT;
            GPIO_Pin2  = MICROPY_HW_UART1_RX_PIN;
            __USART1_CLK_ENABLE();
            break;
        #endif

        #if defined(MICROPY_HW_UART2_PORT) && defined(MICROPY_HW_UART2_PINS)
        case PYB_UART_2:
            UARTx = USART2;
            irqn = USART2_IRQn;
            GPIO_AF_UARTx = GPIO_AF7_USART2;
            GPIO_Port = MICROPY_HW_UART2_PORT;
            GPIO_Pin = MICROPY_HW_UART2_PINS;
            #if defined(MICROPY_HW_UART2_RTS)
            if (uart_obj->uart.Init.HwFlowCtl & UART_HWCONTROL_RTS) {
                GPIO_Pin |= MICROPY_HW_UART2_RTS;
            }
            #endif
            #if defined(MICROPY_HW_UART2_CTS)
            if (uart_obj->uart.Init.HwFlowCtl & UART_HWCONTROL_CTS) {
                GPIO_Pin |= MICROPY_HW_UART2_CTS;
            }
            #endif
            __USART2_CLK_ENABLE();
            break;
        #endif

        #if defined(USART3) && defined(MICROPY_HW_UART3_PORT) && defined(MICROPY_HW_UART3_PINS)
        // USART3 is on PB10/PB11 (CK,CTS,RTS on PB12,PB13,PB14), PC10/PC11 (CK on PC12), PD8/PD9 (CK on PD10)
        case PYB_UART_3:
            UARTx = USART3;
            irqn = USART3_IRQn;
            GPIO_AF_UARTx = GPIO_AF7_USART3;
            GPIO_Port = MICROPY_HW_UART3_PORT;
            GPIO_Pin = MICROPY_HW_UART3_PINS;
            #if defined(MICROPY_HW_UART3_RTS)
            if (uart_obj->uart.Init.HwFlowCtl & UART_HWCONTROL_RTS) {
                GPIO_Pin |= MICROPY_HW_UART3_RTS;
            }
            #endif
            #if defined(MICROPY_HW_UART3_CTS)
            if (uart_obj->uart.Init.HwFlowCtl & UART_HWCONTROL_CTS) {
                GPIO_Pin |= MICROPY_HW_UART3_CTS;
            }
            #endif
            __USART3_CLK_ENABLE();
            break;
        #endif

        #if defined(UART4) && defined(MICROPY_HW_UART4_PORT) && defined(MICROPY_HW_UART4_PINS)
        // UART4 is on PA0/PA1, PC10/PC11
        case PYB_UART_4:
            UARTx = UART4;
            irqn = UART4_IRQn;
            GPIO_AF_UARTx = GPIO_AF8_UART4;
            GPIO_Port = MICROPY_HW_UART4_PORT;
            GPIO_Pin = MICROPY_HW_UART4_PINS;
            __UART4_CLK_ENABLE();
            break;
        #endif

        #if defined(UART5) && \
            defined(MICROPY_HW_UART5_TX_PORT) && \
            defined(MICROPY_HW_UART5_TX_PIN) && \
            defined(MICROPY_HW_UART5_RX_PORT) && \
            defined(MICROPY_HW_UART5_RX_PIN)
        case PYB_UART_5:
            UARTx = UART5;
            irqn = UART5_IRQn;
            GPIO_AF_UARTx = GPIO_AF8_UART5;
            GPIO_Port = MICROPY_HW_UART5_TX_PORT;
            GPIO_Port2 = MICROPY_HW_UART5_RX_PORT;
            GPIO_Pin = MICROPY_HW_UART5_TX_PIN;
            GPIO_Pin2 = MICROPY_HW_UART5_RX_PIN;
            __UART5_CLK_ENABLE();
            break;
        #endif

        #if defined(MICROPY_HW_UART6_PORT) && defined(MICROPY_HW_UART6_PINS)
        // USART6 is on PC6/PC7 (CK on PC8)
        case PYB_UART_6:
            UARTx = USART6;
            irqn = USART6_IRQn;
            GPIO_AF_UARTx = GPIO_AF8_USART6;
            GPIO_Port = MICROPY_HW_UART6_PORT;
            GPIO_Pin = MICROPY_HW_UART6_PINS;
            __USART6_CLK_ENABLE();
            break;
        #endif

        default:
            // UART does not exist or is not configured for this board
            return false;
    }

    uart_obj->irqn = irqn;
    uart_obj->uart.Instance = UARTx;

    // init GPIO
    mp_hal_gpio_clock_enable(GPIO_Port);
    GPIO_InitTypeDef GPIO_InitStructure;
    GPIO_InitStructure.Pin = GPIO_Pin;
    GPIO_InitStructure.Speed = GPIO_SPEED_HIGH;
    GPIO_InitStructure.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStructure.Pull = GPIO_PULLUP;
    GPIO_InitStructure.Alternate = GPIO_AF_UARTx;
    HAL_GPIO_Init(GPIO_Port, &GPIO_InitStructure);

    // init GPIO for second pin if needed
    if (GPIO_Port2 != NULL) {
        mp_hal_gpio_clock_enable(GPIO_Port2);
        GPIO_InitStructure.Pin = GPIO_Pin2;
        HAL_GPIO_Init(GPIO_Port2, &GPIO_InitStructure);
    }

    // init UARTx
    HAL_UART_Init(&uart_obj->uart);

    uart_obj->is_enabled = true;

    return true;
}

/* obsolete and unused
bool uart_init(pyb_uart_obj_t *uart_obj, uint32_t baudrate) {
    UART_HandleTypeDef *uh = &uart_obj->uart;
    memset(uh, 0, sizeof(*uh));
    uh->Init.BaudRate = baudrate;
    uh->Init.WordLength = UART_WORDLENGTH_8B;
    uh->Init.StopBits = UART_STOPBITS_1;
    uh->Init.Parity = UART_PARITY_NONE;
    uh->Init.Mode = UART_MODE_TX_RX;
    uh->Init.HwFlowCtl = UART_HWCONTROL_NONE;
    uh->Init.OverSampling = UART_OVERSAMPLING_16;
    return uart_init2(uart_obj);
}
*/

mp_uint_t uart_rx_any(pyb_uart_obj_t *self) {
    int buffer_bytes = self->read_buf_head - self->read_buf_tail;
    if (buffer_bytes < 0) {
        return buffer_bytes + self->read_buf_len;
    } else if (buffer_bytes > 0) {
        return buffer_bytes;
    } else {
        return __HAL_UART_GET_FLAG(&self->uart, UART_FLAG_RXNE) != RESET;
    }
}

// Waits at most timeout milliseconds for at least 1 char to become ready for
// reading (from buf or for direct reading).
// Returns true if something available, false if not.
STATIC bool uart_rx_wait(pyb_uart_obj_t *self, uint32_t timeout) {
    uint32_t start = HAL_GetTick();
    for (;;) {
        if (self->read_buf_tail != self->read_buf_head || __HAL_UART_GET_FLAG(&self->uart, UART_FLAG_RXNE) != RESET) {
            return true; // have at least 1 char ready for reading
        }
        if (HAL_GetTick() - start >= timeout) {
            return false; // timeout
        }
        __WFI();
    }
}

// assumes there is a character available
int uart_rx_char(pyb_uart_obj_t *self) {
    if (self->read_buf_tail != self->read_buf_head) {
        // buffering via IRQ
        int data;
        if (self->char_width == CHAR_WIDTH_9BIT) {
            data = ((uint16_t*)self->read_buf)[self->read_buf_tail];
        } else {
            data = self->read_buf[self->read_buf_tail];
        }
        self->read_buf_tail = (self->read_buf_tail + 1) % self->read_buf_len;
        if (__HAL_UART_GET_FLAG(&self->uart, UART_FLAG_RXNE) != RESET) {
            // UART was stalled by flow ctrl: re-enable IRQ now we have room in buffer
            __HAL_UART_ENABLE_IT(&self->uart, UART_IT_RXNE);
        }
        return data;
    } else {
        // no buffering
        #if defined(MCU_SERIES_F7) || defined(MCU_SERIES_L4)
        return self->uart.Instance->RDR & self->char_mask;
        #else
        return self->uart.Instance->DR & self->char_mask;
        #endif
    }
}

// Waits at most timeout milliseconds for TX register to become empty.
// Returns true if can write, false if can't.
STATIC bool uart_tx_wait(pyb_uart_obj_t *self, uint32_t timeout) {
    uint32_t start = HAL_GetTick();
    for (;;) {
        if (__HAL_UART_GET_FLAG(&self->uart, UART_FLAG_TXE)) {
            return true; // tx register is empty
        }
        if (HAL_GetTick() - start >= timeout) {
            return false; // timeout
        }
        __WFI();
    }
}

STATIC HAL_StatusTypeDef uart_tx_data(pyb_uart_obj_t *self, uint8_t *data, uint16_t len) {
    if (self->uart.Init.HwFlowCtl & UART_HWCONTROL_CTS) {
        // CTS can hold off transmission for an arbitrarily long time. Apply
        // the overall timeout rather than the character timeout.
        return HAL_UART_Transmit(&self->uart, data, len, self->timeout);
    }
    // The timeout specified here is for waiting for the TX data register to
    // become empty (ie between chars), as well as for the final char to be
    // completely transferred.  The default value for timeout_char is long
    // enough for 1 char, but we need to double it to wait for the last char
    // to be transferred to the data register, and then to be transmitted.
    return HAL_UART_Transmit(&self->uart, data, len, 2 * self->timeout_char);
}

STATIC void uart_tx_char(pyb_uart_obj_t *uart_obj, int c) {
    uint8_t ch = c;
    uart_tx_data(uart_obj, &ch, 1);
}

void uart_tx_strn(pyb_uart_obj_t *uart_obj, const char *str, uint len) {
    uart_tx_data(uart_obj, (uint8_t*)str, len);
}

void uart_tx_strn_cooked(pyb_uart_obj_t *uart_obj, const char *str, uint len) {
    for (const char *top = str + len; str < top; str++) {
        if (*str == '\n') {
            uart_tx_char(uart_obj, '\r');
        }
        uart_tx_char(uart_obj, *str);
    }
}

// this IRQ handler is set up to handle RXNE interrupts only
void uart_irq_handler(mp_uint_t uart_id) {
    // get the uart object
    pyb_uart_obj_t *self = MP_STATE_PORT(pyb_uart_obj_all)[uart_id - 1];

    if (self == NULL) {
        // UART object has not been set, so we can't do anything, not
        // even disable the IRQ.  This should never happen.
        return;
    }

    if (__HAL_UART_GET_FLAG(&self->uart, UART_FLAG_RXNE) != RESET) {
        if (self->read_buf_len != 0) {
            uint16_t next_head = (self->read_buf_head + 1) % self->read_buf_len;
            if (next_head != self->read_buf_tail) {
                // only read data if room in buf
                #if defined(MCU_SERIES_F7) || defined(MCU_SERIES_L4)
                int data = self->uart.Instance->RDR; // clears UART_FLAG_RXNE
                #else
                int data = self->uart.Instance->DR; // clears UART_FLAG_RXNE
                #endif
                data &= self->char_mask;
                if (self->char_width == CHAR_WIDTH_9BIT) {
                    ((uint16_t*)self->read_buf)[self->read_buf_head] = data;
                } else {
                    self->read_buf[self->read_buf_head] = data;
                }
                self->read_buf_head = next_head;
            } else { // No room: leave char in buf, disable interrupt
                __HAL_UART_DISABLE_IT(&self->uart, UART_IT_RXNE);
            }
        }
    }
}

/******************************************************************************/
/* Micro Python bindings                                                      */

STATIC void pyb_uart_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
    pyb_uart_obj_t *self = self_in;
    if (!self->is_enabled) {
        mp_printf(print, "UART(%u)", self->uart_id);
    } else {
        mp_int_t bits = (self->uart.Init.WordLength == UART_WORDLENGTH_8B ? 8 : 9);
        if (self->uart.Init.Parity != UART_PARITY_NONE) {
            bits -= 1;
        }
        mp_printf(print, "UART(%u, baudrate=%u, bits=%u, parity=",
            self->uart_id, self->uart.Init.BaudRate, bits);
        if (self->uart.Init.Parity == UART_PARITY_NONE) {
            mp_print_str(print, "None");
        } else {
            mp_printf(print, "%u", self->uart.Init.Parity == UART_PARITY_EVEN ? 0 : 1);
        }
        if (self->uart.Init.HwFlowCtl) {
            mp_printf(print, ", flow=");
            if (self->uart.Init.HwFlowCtl & UART_HWCONTROL_RTS) {
                mp_printf(print, "RTS%s", self->uart.Init.HwFlowCtl & UART_HWCONTROL_CTS ? "|" : "");
            }
            if (self->uart.Init.HwFlowCtl & UART_HWCONTROL_CTS) {
                mp_printf(print, "CTS");
            }
        }
        mp_printf(print, ", stop=%u, timeout=%u, timeout_char=%u, read_buf_len=%u)",
            self->uart.Init.StopBits == UART_STOPBITS_1 ? 1 : 2,
            self->timeout, self->timeout_char,
            self->read_buf_len == 0 ? 0 : self->read_buf_len - 1); // -1 to adjust for usable length of buffer
    }
}

/// \method init(baudrate, bits=8, parity=None, stop=1, *, timeout=1000, timeout_char=0, flow=0, read_buf_len=64)
///
/// Initialise the UART bus with the given parameters:
///
///   - `baudrate` is the clock rate.
///   - `bits` is the number of bits per byte, 7, 8 or 9.
///   - `parity` is the parity, `None`, 0 (even) or 1 (odd).
///   - `stop` is the number of stop bits, 1 or 2.
///   - `timeout` is the timeout in milliseconds to wait for the first character.
///   - `timeout_char` is the timeout in milliseconds to wait between characters.
///   - `flow` is RTS | CTS where RTS == 256, CTS == 512
///   - `read_buf_len` is the character length of the read buffer (0 to disable).
STATIC mp_obj_t pyb_uart_init_helper(pyb_uart_obj_t *self, mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
    static const mp_arg_t allowed_args[] = {
        { MP_QSTR_baudrate, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 9600} },
        { MP_QSTR_bits, MP_ARG_INT, {.u_int = 8} },
        { MP_QSTR_parity, MP_ARG_OBJ, {.u_obj = mp_const_none} },
        { MP_QSTR_stop, MP_ARG_INT, {.u_int = 1} },
        { 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} },
    };

    // parse args
    struct {
        mp_arg_val_t baudrate, bits, parity, stop, flow, timeout, timeout_char, 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);

    // set the UART configuration values
    memset(&self->uart, 0, sizeof(self->uart));
    UART_InitTypeDef *init = &self->uart.Init;

    // baudrate
    init->BaudRate = args.baudrate.u_int;

    // parity
    mp_int_t bits = args.bits.u_int;
    if (args.parity.u_obj == mp_const_none) {
        init->Parity = UART_PARITY_NONE;
    } else {
        mp_int_t parity = mp_obj_get_int(args.parity.u_obj);
        init->Parity = (parity & 1) ? UART_PARITY_ODD : UART_PARITY_EVEN;
        bits += 1; // STs convention has bits including parity
    }

    // number of bits
    if (bits == 8) {
        init->WordLength = UART_WORDLENGTH_8B;
    } else if (bits == 9) {
        init->WordLength = UART_WORDLENGTH_9B;
    } else {
        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "unsupported combination of bits and parity"));
    }

    // stop bits
    switch (args.stop.u_int) {
        case 1: init->StopBits = UART_STOPBITS_1; break;
        default: init->StopBits = UART_STOPBITS_2; break;
    }

    // flow control
    init->HwFlowCtl = args.flow.u_int;

    // extra config (not yet configurable)
    init->Mode = UART_MODE_TX_RX;
    init->OverSampling = UART_OVERSAMPLING_16;

    // init UART (if it fails, it's because the port doesn't exist)
    if (!uart_init2(self)) {
        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART(%d) does not exist", self->uart_id));
    }

    // set timeout
    self->timeout = args.timeout.u_int;

    // set timeout_char
    // make sure it is at least as long as a whole character (13 bits to be safe)
    self->timeout_char = args.timeout_char.u_int;
    uint32_t min_timeout_char = 13000 / init->BaudRate + 1;
    if (self->timeout_char < min_timeout_char) {
        self->timeout_char = min_timeout_char;
    }

    // setup the read buffer
    m_del(byte, self->read_buf, self->read_buf_len << self->char_width);
    if (init->WordLength == UART_WORDLENGTH_9B && init->Parity == UART_PARITY_NONE) {
        self->char_mask = 0x1ff;
        self->char_width = CHAR_WIDTH_9BIT;
    } else {
        if (init->WordLength == UART_WORDLENGTH_9B || init->Parity == UART_PARITY_NONE) {
            self->char_mask = 0xff;
        } else {
            self->char_mask = 0x7f;
        }
        self->char_width = CHAR_WIDTH_8BIT;
    }
    self->read_buf_head = 0;
    self->read_buf_tail = 0;
    if (args.read_buf_len.u_int <= 0) {
        // no read buffer
        self->read_buf_len = 0;
        self->read_buf = NULL;
        HAL_NVIC_DisableIRQ(self->irqn);
        __HAL_UART_DISABLE_IT(&self->uart, UART_IT_RXNE);
    } else {
        // read buffer using interrupts
        self->read_buf_len = args.read_buf_len.u_int + 1; // +1 to adjust for usable length of buffer
        self->read_buf = m_new(byte, self->read_buf_len << self->char_width);
        __HAL_UART_ENABLE_IT(&self->uart, UART_IT_RXNE);
        HAL_NVIC_SetPriority(self->irqn, IRQ_PRI_UART, IRQ_SUBPRI_UART);
        HAL_NVIC_EnableIRQ(self->irqn);
    }

    // compute actual baudrate that was configured
    // (this formula assumes UART_OVERSAMPLING_16)
    uint32_t actual_baudrate;
    if (self->uart.Instance == USART1
        #if defined(USART6)
        || self->uart.Instance == USART6
        #endif
        ) {
        actual_baudrate = HAL_RCC_GetPCLK2Freq();
    } else {
        actual_baudrate = HAL_RCC_GetPCLK1Freq();
    }
    actual_baudrate /= self->uart.Instance->BRR;

    // check we could set the baudrate within 5%
    uint32_t baudrate_diff;
    if (actual_baudrate > init->BaudRate) {
        baudrate_diff = actual_baudrate - init->BaudRate;
    } else {
        baudrate_diff = init->BaudRate - actual_baudrate;
    }
    init->BaudRate = actual_baudrate; // remember actual baudrate for printing
    if (20 * baudrate_diff > init->BaudRate) {
        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "set baudrate %d is not within 5%% of desired value", actual_baudrate));
    }

    return mp_const_none;
}

/// \classmethod \constructor(bus, ...)
///
/// Construct a UART object on the given bus.  `bus` can be 1-6, or 'XA', 'XB', 'YA', or 'YB'.
/// With no additional parameters, the UART object is created but not
/// initialised (it has the settings from the last initialisation of
/// the bus, if any).  If extra arguments are given, the bus is initialised.
/// See `init` for parameters of initialisation.
///
/// The physical pins of the UART busses are:
///
///   - `UART(4)` is on `XA`: `(TX, RX) = (X1, X2) = (PA0, PA1)`
///   - `UART(1)` is on `XB`: `(TX, RX) = (X9, X10) = (PB6, PB7)`
///   - `UART(6)` is on `YA`: `(TX, RX) = (Y1, Y2) = (PC6, PC7)`
///   - `UART(3)` is on `YB`: `(TX, RX) = (Y9, Y10) = (PB10, PB11)`
///   - `UART(2)` is on: `(TX, RX) = (X3, X4) = (PA2, PA3)`
STATIC mp_obj_t pyb_uart_make_new(const mp_obj_type_t *type, mp_uint_t n_args, mp_uint_t n_kw, const mp_obj_t *args) {
    // check arguments
    mp_arg_check_num(n_args, n_kw, 1, MP_OBJ_FUN_ARGS_MAX, true);

    // work out port
    int uart_id = 0;
    if (MP_OBJ_IS_STR(args[0])) {
        const char *port = mp_obj_str_get_str(args[0]);
        if (0) {
        #ifdef MICROPY_HW_UART1_NAME
        } else if (strcmp(port, MICROPY_HW_UART1_NAME) == 0) {
            uart_id = PYB_UART_1;
        #endif
        #ifdef MICROPY_HW_UART2_NAME
        } else if (strcmp(port, MICROPY_HW_UART2_NAME) == 0) {
            uart_id = PYB_UART_2;
        #endif
        #ifdef MICROPY_HW_UART3_NAME
        } else if (strcmp(port, MICROPY_HW_UART3_NAME) == 0) {
            uart_id = PYB_UART_3;
        #endif
        #ifdef MICROPY_HW_UART4_NAME
        } else if (strcmp(port, MICROPY_HW_UART4_NAME) == 0) {
            uart_id = PYB_UART_4;
        #endif
        #ifdef MICROPY_HW_UART5_NAME
        } else if (strcmp(port, MICROPY_HW_UART5_NAME) == 0) {
            uart_id = PYB_UART_5;
        #endif
        #ifdef MICROPY_HW_UART6_NAME
        } else if (strcmp(port, MICROPY_HW_UART6_NAME) == 0) {
            uart_id = PYB_UART_6;
        #endif
        } else {
            nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART(%s) does not exist", port));
        }
    } else {
        uart_id = mp_obj_get_int(args[0]);
        if (uart_id < 1 || uart_id > MP_ARRAY_SIZE(MP_STATE_PORT(pyb_uart_obj_all))) {
            nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART(%d) does not exist", uart_id));
        }
    }

    pyb_uart_obj_t *self;
    if (MP_STATE_PORT(pyb_uart_obj_all)[uart_id - 1] == NULL) {
        // create new UART object
        self = m_new0(pyb_uart_obj_t, 1);
        self->base.type = &pyb_uart_type;
        self->uart_id = uart_id;
        MP_STATE_PORT(pyb_uart_obj_all)[uart_id - 1] = self;
    } else {
        // reference existing UART object
        self = MP_STATE_PORT(pyb_uart_obj_all)[uart_id - 1];
    }

    if (n_args > 1 || n_kw > 0) {
        // start the peripheral
        mp_map_t kw_args;
        mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
        pyb_uart_init_helper(self, n_args - 1, args + 1, &kw_args);
    }

    return self;
}

STATIC mp_obj_t pyb_uart_init(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
    return pyb_uart_init_helper(args[0], n_args - 1, args + 1, kw_args);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_uart_init_obj, 1, pyb_uart_init);

/// \method deinit()
/// Turn off the UART bus.
STATIC mp_obj_t pyb_uart_deinit(mp_obj_t self_in) {
    pyb_uart_obj_t *self = self_in;
    self->is_enabled = false;
    UART_HandleTypeDef *uart = &self->uart;
    HAL_UART_DeInit(uart);
    if (uart->Instance == USART1) {
        HAL_NVIC_DisableIRQ(USART1_IRQn);
        __USART1_FORCE_RESET();
        __USART1_RELEASE_RESET();
        __USART1_CLK_DISABLE();
    } else if (uart->Instance == USART2) {
        HAL_NVIC_DisableIRQ(USART2_IRQn);
        __USART2_FORCE_RESET();
        __USART2_RELEASE_RESET();
        __USART2_CLK_DISABLE();
    #if defined(USART3)
    } else if (uart->Instance == USART3) {
        HAL_NVIC_DisableIRQ(USART3_IRQn);
        __USART3_FORCE_RESET();
        __USART3_RELEASE_RESET();
        __USART3_CLK_DISABLE();
    #endif
    #if defined(UART4)
    } else if (uart->Instance == UART4) {
        HAL_NVIC_DisableIRQ(UART4_IRQn);
        __UART4_FORCE_RESET();
        __UART4_RELEASE_RESET();
        __UART4_CLK_DISABLE();
    #endif
    #if defined(UART5)
    } else if (uart->Instance == UART5) {
        HAL_NVIC_DisableIRQ(UART5_IRQn);
        __UART5_FORCE_RESET();
        __UART5_RELEASE_RESET();
        __UART5_CLK_DISABLE();
    #endif
    #if defined(UART6)
    } else if (uart->Instance == USART6) {
        HAL_NVIC_DisableIRQ(USART6_IRQn);
        __USART6_FORCE_RESET();
        __USART6_RELEASE_RESET();
        __USART6_CLK_DISABLE();
    #endif
    }
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_deinit_obj, pyb_uart_deinit);

/// \method any()
/// Return `True` if any characters waiting, else `False`.
STATIC mp_obj_t pyb_uart_any(mp_obj_t self_in) {
    pyb_uart_obj_t *self = self_in;
    return MP_OBJ_NEW_SMALL_INT(uart_rx_any(self));
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_any_obj, pyb_uart_any);

/// \method writechar(char)
/// Write a single character on the bus.  `char` is an integer to write.
/// Return value: `None`.
STATIC mp_obj_t pyb_uart_writechar(mp_obj_t self_in, mp_obj_t char_in) {
    pyb_uart_obj_t *self = self_in;

    // get the character to write (might be 9 bits)
    uint16_t data = mp_obj_get_int(char_in);

    // write the character
    HAL_StatusTypeDef status;
    if (uart_tx_wait(self, self->timeout)) {
        status = uart_tx_data(self, (uint8_t*)&data, 1);
    } else {
        status = HAL_TIMEOUT;
    }

    if (status != HAL_OK) {
        mp_hal_raise(status);
    }

    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_2(pyb_uart_writechar_obj, pyb_uart_writechar);

/// \method readchar()
/// Receive a single character on the bus.
/// Return value: The character read, as an integer.  Returns -1 on timeout.
STATIC mp_obj_t pyb_uart_readchar(mp_obj_t self_in) {
    pyb_uart_obj_t *self = self_in;
    if (uart_rx_wait(self, self->timeout)) {
        return MP_OBJ_NEW_SMALL_INT(uart_rx_char(self));
    } else {
        // return -1 on timeout
        return MP_OBJ_NEW_SMALL_INT(-1);
    }
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_readchar_obj, pyb_uart_readchar);

// uart.sendbreak()
STATIC mp_obj_t pyb_uart_sendbreak(mp_obj_t self_in) {
    pyb_uart_obj_t *self = self_in;
    #if defined(MCU_SERIES_F7) || defined(MCU_SERIES_L4)
    self->uart.Instance->RQR = USART_RQR_SBKRQ; // write-only register
    #else
    self->uart.Instance->CR1 |= USART_CR1_SBK;
    #endif
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_sendbreak_obj, pyb_uart_sendbreak);

STATIC const mp_map_elem_t pyb_uart_locals_dict_table[] = {
    // instance methods

    { MP_OBJ_NEW_QSTR(MP_QSTR_init), (mp_obj_t)&pyb_uart_init_obj },
    { MP_OBJ_NEW_QSTR(MP_QSTR_deinit), (mp_obj_t)&pyb_uart_deinit_obj },
    { MP_OBJ_NEW_QSTR(MP_QSTR_any), (mp_obj_t)&pyb_uart_any_obj },

    /// \method read([nbytes])
    { MP_OBJ_NEW_QSTR(MP_QSTR_read), (mp_obj_t)&mp_stream_read_obj },
    /// \method readall()
    { MP_OBJ_NEW_QSTR(MP_QSTR_readall), (mp_obj_t)&mp_stream_readall_obj },
    /// \method readline()
    { MP_OBJ_NEW_QSTR(MP_QSTR_readline), (mp_obj_t)&mp_stream_unbuffered_readline_obj},
    /// \method readinto(buf[, nbytes])
    { MP_OBJ_NEW_QSTR(MP_QSTR_readinto), (mp_obj_t)&mp_stream_readinto_obj },
    /// \method write(buf)
    { MP_OBJ_NEW_QSTR(MP_QSTR_write), (mp_obj_t)&mp_stream_write_obj },

    { MP_OBJ_NEW_QSTR(MP_QSTR_writechar), (mp_obj_t)&pyb_uart_writechar_obj },
    { MP_OBJ_NEW_QSTR(MP_QSTR_readchar), (mp_obj_t)&pyb_uart_readchar_obj },
    { MP_OBJ_NEW_QSTR(MP_QSTR_sendbreak), (mp_obj_t)&pyb_uart_sendbreak_obj },

    // class constants
    { MP_OBJ_NEW_QSTR(MP_QSTR_RTS), MP_OBJ_NEW_SMALL_INT(UART_HWCONTROL_RTS) },
    { MP_OBJ_NEW_QSTR(MP_QSTR_CTS), MP_OBJ_NEW_SMALL_INT(UART_HWCONTROL_CTS) },
};

STATIC MP_DEFINE_CONST_DICT(pyb_uart_locals_dict, pyb_uart_locals_dict_table);

STATIC mp_uint_t pyb_uart_read(mp_obj_t self_in, void *buf_in, mp_uint_t size, int *errcode) {
    pyb_uart_obj_t *self = self_in;
    byte *buf = buf_in;

    // check that size is a multiple of character width
    if (size & self->char_width) {
        *errcode = MP_EIO;
        return MP_STREAM_ERROR;
    }

    // convert byte size to char size
    size >>= self->char_width;

    // make sure we want at least 1 char
    if (size == 0) {
        return 0;
    }

    // wait for first char to become available
    if (!uart_rx_wait(self, self->timeout)) {
        // return EAGAIN error to indicate non-blocking (then read() method returns None)
        *errcode = MP_EAGAIN;
        return MP_STREAM_ERROR;
    }

    // read the data
    byte *orig_buf = buf;
    for (;;) {
        int data = uart_rx_char(self);
        if (self->char_width == CHAR_WIDTH_9BIT) {
            *(uint16_t*)buf = data;
            buf += 2;
        } else {
            *buf++ = data;
        }
        if (--size == 0 || !uart_rx_wait(self, self->timeout_char)) {
            // return number of bytes read
            return buf - orig_buf;
        }
    }
}

STATIC mp_uint_t pyb_uart_write(mp_obj_t self_in, const void *buf_in, mp_uint_t size, int *errcode) {
    pyb_uart_obj_t *self = self_in;
    const byte *buf = buf_in;

    // check that size is a multiple of character width
    if (size & self->char_width) {
        *errcode = MP_EIO;
        return MP_STREAM_ERROR;
    }

    // wait to be able to write the first character. EAGAIN causes write to return None
    if (!uart_tx_wait(self, self->timeout)) {
        *errcode = MP_EAGAIN;
        return MP_STREAM_ERROR;
    }

    // write the data
    HAL_StatusTypeDef status = uart_tx_data(self, (uint8_t*)buf, size >> self->char_width);

    if (status == HAL_OK) {
        // return number of bytes written
        return size;
    } else if (status == HAL_TIMEOUT) { // UART_WaitOnFlagUntilTimeout() disables RXNE interrupt on timeout
        if (self->read_buf_len > 0) {
            __HAL_UART_ENABLE_IT(&self->uart, UART_IT_RXNE); // re-enable RXNE
        }
        // return number of bytes written
        if (self->char_width == CHAR_WIDTH_8BIT) {
            return size - self->uart.TxXferCount - 1;
        } else {
            int written = self->uart.TxXferCount * 2;
            return size - written - 2;
        }
    } else {
        *errcode = mp_hal_status_to_errno_table[status];
        return MP_STREAM_ERROR;
    }
}

STATIC mp_uint_t pyb_uart_ioctl(mp_obj_t self_in, mp_uint_t request, mp_uint_t arg, int *errcode) {
    pyb_uart_obj_t *self = self_in;
    mp_uint_t ret;
    if (request == MP_IOCTL_POLL) {
        mp_uint_t flags = arg;
        ret = 0;
        if ((flags & MP_IOCTL_POLL_RD) && uart_rx_any(self)) {
            ret |= MP_IOCTL_POLL_RD;
        }
        if ((flags & MP_IOCTL_POLL_WR) && __HAL_UART_GET_FLAG(&self->uart, UART_FLAG_TXE)) {
            ret |= MP_IOCTL_POLL_WR;
        }
    } else {
        *errcode = MP_EINVAL;
        ret = MP_STREAM_ERROR;
    }
    return ret;
}

STATIC const mp_stream_p_t uart_stream_p = {
    .read = pyb_uart_read,
    .write = pyb_uart_write,
    .ioctl = pyb_uart_ioctl,
    .is_text = false,
};

const mp_obj_type_t pyb_uart_type = {
    { &mp_type_type },
    .name = MP_QSTR_UART,
    .print = pyb_uart_print,
    .make_new = pyb_uart_make_new,
    .getiter = mp_identity,
    .iternext = mp_stream_unbuffered_iter,
    .protocol = &uart_stream_p,
    .locals_dict = (mp_obj_t)&pyb_uart_locals_dict,
};