Earle F. Philhower, III
5e74bbbbb2
The SerialPIO(SoftwareSerial) receive path was convoluted and required a lot of work on the host to get the actual data out. It also wasn't always sampling on the proper edge leading to errors whenever clocks or hold times shifted slightly. Rewrite the SerialPIO RX path to explicitily wait for start bit, pause 1/2 bit time, then idle for a full bit time for all bits. Takes more PIO instruction memory but works flawlessly even with mismatched clocks. Tested with a loopback from HW UART to SW UART with a 5% clock mismatch @ 19200 baud without reception errors, whereas the original code would fail with less than a 0.5% variation. Fixes #2928 ```` SoftwareSerial s(15, -1); void setup() { Serial1.setTX(0); Serial1.begin(19200 + 1920/2, SERIAL_8N1); s.begin(19200, SERIAL_8N1); } void loop() { Serial.println("---"); Serial1.write("Had we but world enough and time", 32); uint32_t now = millis(); while (millis() - now < 500) { while (s.available()) { auto c = s.read(); Serial.printf("%02x '%c'\n", c, c); } } } ````
112 lines
3.3 KiB
Plaintext
112 lines
3.3 KiB
Plaintext
; pio_uart for the Raspberry Pi Pico RP2040
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;
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; Based loosely off of the uart_rx/_tx examples in the pico-examples repo,
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; but heavily modified and optimized to not require changing the PIO
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; clocks so that Tone and Servo won't be affected, and multiple different
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; PIO ports can be run at different baud at the same time.
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;
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; Copyright (c) 2021 Earle F. Philhower, III <earlephilhower@yahoo.com>
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;
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; This library is free software; you can redistribute it and/or
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; modify it under the terms of the GNU Lesser General Public
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; License as published by the Free Software Foundation; either
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; version 2.1 of the License, or (at your option) any later version.
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;
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; This library is distributed in the hope that it will be useful,
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; but WITHOUT ANY WARRANTY; without even the implied warranty of
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; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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; Lesser General Public License for more details.
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;
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; You should have received a copy of the GNU Lesser General Public
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; License along with this library; if not, write to the Free Software
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; Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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.program pio_tx
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.side_set 1 opt
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; We shift out the start and stop bit as part of the FIFO
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set x, 9
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pull side 1 ; Force stop bit high
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; Send the bits
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bitloop:
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out pins, 1
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mov y, isr ; ISR is loaded by the setup routine with the period-1 count
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wait_bit:
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jmp y-- wait_bit
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jmp x-- bitloop
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% c-sdk {
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static inline void pio_tx_program_init(PIO pio, uint sm, uint offset, uint pin_tx) {
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// Tell PIO to initially drive output-high on the selected pin, then map PIO
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// onto that pin with the IO muxes.
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pio_sm_set_set_pins(pio, sm, pin_tx, 1);
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pio_sm_set_consecutive_pindirs(pio, sm, pin_tx, 1, true);
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pio_gpio_init(pio, pin_tx);
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pio_sm_config c = pio_tx_program_get_default_config(offset);
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// OUT shifts to right, no autopull
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sm_config_set_out_shift(&c, true, false, 32);
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// We are mapping both OUT and side-set to the same pin, because sometimes
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// we need to assert user data onto the pin (with OUT) and sometimes
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// assert constant values (start/stop bit)
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sm_config_set_out_pins(&c, pin_tx, 1);
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sm_config_set_sideset_pins(&c, pin_tx);
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// We only need TX, so get an 8-deep FIFO!
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sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);
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pio_sm_init(pio, sm, offset, &c);
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}
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%}
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.program pio_rx
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; IN pin 0 and JMP pin are both mapped to the GPIO used as UART RX.
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start:
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set x, 18 ; Preload bit counter...overwritten by the app
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wait 0 pin 0 ; Stall until start bit is asserted
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; Delay until 1/2 way into the bit time
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mov y, osr
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wait_mid_start:
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jmp y-- wait_mid_start
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bitloop:
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mov y, osr
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bitloop1:
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jmp y-- bitloop1
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mov y, osr
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bitloop2:
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jmp y-- bitloop2
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in pins, 1
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jmp x-- bitloop
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push
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% c-sdk {
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static inline void pio_rx_program_init(PIO pio, uint sm, uint offset, uint pin) {
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pio_sm_set_consecutive_pindirs(pio, sm, pin, 1, false);
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pio_gpio_init(pio, pin);
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gpio_pull_up(pin);
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pio_sm_config c = pio_rx_program_get_default_config(offset);
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sm_config_set_in_pins(&c, pin); // for WAIT, IN
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sm_config_set_jmp_pin(&c, pin); // for JMP
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// Shift to right, autopull disabled
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sm_config_set_in_shift(&c, true, false, 32);
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pio_sm_init(pio, sm, offset, &c);
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}
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%}
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