tsoftuart: add a softare timer base UART driver, and example.

examples/tsoftuart/.gitignore

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+!local.mk

examples/tsoftuart/FreeRTOSConfig.h

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+#define configUSE_TRACE_FACILITY 1
+#define configGENERATE_RUN_TIME_STATS 1
+#define portGET_RUN_TIME_COUNTER_VALUE() (RTC.COUNTER)
+#define portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() {}
+
+/* Use the defaults for everything else */
+#include_next<FreeRTOSConfig.h>

examples/tsoftuart/Makefile

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+# Makefile for tsfotuart example
+PROGRAM=tsoftuart
+EXTRA_COMPONENTS=extras/dhcpserver extras/wificfg extras/mactimer extras/tsoftuart
+
+# For the mDNS responder included with lwip:
+EXTRA_CFLAGS += -DLWIP_MDNS_RESPONDER=1 -DLWIP_NUM_NETIF_CLIENT_DATA=1 -DLWIP_NETIF_EXT_STATUS_CALLBACK=1
+
+# Avoid writing the wifi state to flash when using wificfg.
+EXTRA_CFLAGS += -DWIFI_PARAM_SAVE=0
+
+EXTRA_CFLAGS += -DWIFICFG_CLIENT_TASK=1 -DWIFICFG_IRAM_TEST=1
+
+include ../../common.mk

examples/tsoftuart/local.mk

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+FLASH_SIZE ?= 32

examples/tsoftuart/tsoftuart.c

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+/*
+ * Example timer based software UART drive.
+ *
+ * Copyright (C) 2019 OurAirQuality.org
+ *
+ * Licensed under the Apache License, Version 2.0, January 2004 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *      http://www.apache.org/licenses/
+ *
+ * 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 CONTRIBUTORS 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 WITH THE SOFTWARE.
+ *
+ */
+
+#include <string.h>
+#include <ctype.h>
+
+#include <espressif/esp_common.h>
+#include <espressif/user_interface.h>
+#include <esp/uart.h>
+#include <FreeRTOS.h>
+#include <task.h>
+
+#include "lwip/sockets.h"
+
+#include "wificfg/wificfg.h"
+#include "tsoftuart/tsoftuart.h"
+
+static void tsoftuart_task(void *pvParameters)
+{
+    /* Initialize the UART Tx. */
+    uint32_t tx_pin = *(uint32_t *)pvParameters;
+    struct tsoftuart *uart = tsoftuart_init(tx_pin, 9600);
+    
+    for (;;) {
+        /* Reset the timing error records. */
+        uart->output_queue_error_low = 0;
+        uart->output_queue_error_high = 0;
+
+        char str[] = "Hello 0123456789 abcdefghijklmnopqrstuvwxyz\r\n";
+        for (size_t i = 0; i < strlen(str); i++) {
+            tsoftuart_putc(uart, str[i]);
+        }
+
+        /* Check the timing error. */
+        if (uart->output_queue_error_high > 2 || uart->output_queue_error_low < -2) {
+            tsoftuart_write(uart, "X\r\n", 3);
+        }
+
+        vTaskDelay(200 / portTICK_PERIOD_MS);
+    }
+}
+
+void user_init(void)
+{
+    uart_set_baud(0, 115200);
+    printf("SDK version:%s\n", sdk_system_get_sdk_version());
+
+    wificfg_init(80, NULL);
+
+    /* Start two tasks writing to different pins. */
+
+    static uint32_t tx_pin1 = 1;
+    xTaskCreate(&tsoftuart_task, "tsoftuart1", 256, &tx_pin1, 1, NULL);
+
+    static uint32_t tx_pin2 = 2;
+    xTaskCreate(&tsoftuart_task, "tsoftuart2", 256, &tx_pin2, 1, NULL);
+}

extras/tsoftuart/component.mk

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+# Component makefile for extras/tsoftuart
+
+# Expected anyone using tsoftuart includes it as 'tsoftuart/tsoftuart.h'
+INC_DIRS += $(tsoftuart_ROOT)..
+
+# args for passing into compile rule generation
+tsoftuart_INC_DIR =
+tsoftuart_SRC_DIR = $(tsoftuart_ROOT)
+
+$(eval $(call component_compile_rules,tsoftuart))

extras/tsoftuart/tsoftuart.c

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+/*
+ * Software timer based UART driver.
+ *
+ * Copyright (C) 2018 to 2019 OurAirQuality.org
+ *
+ * Licensed under the Apache License, Version 2.0, January 2004 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *      http://www.apache.org/licenses/
+ *
+ * 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 CONTRIBUTORS 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 WITH THE SOFTWARE.
+ *
+ */
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <esp/uart.h>
+#include <stdio.h>
+#include <espressif/esp_system.h>
+#include "FreeRTOS.h"
+#include "task.h"
+#include "tsoftuart/tsoftuart.h"
+
+
+/*
+ * The design builds a sequence of UART output transitions - the delay between
+ * each toggling of the output. This sequence is then followed by a timer and
+ * the timer handler toggles the state and resets the timer for the next
+ * transition until done. This design avoids the code having to spin to
+ * implement delays, and avoid having to disable interrupts for more reliable
+ * timing.
+ *
+ * The MAC timer interrupt is used here as it has a high priority which helps
+ * keep accurate output transition times. The MAC timer interrupt is a NMI and
+ * the handler needs to take care not to interact widely. The handler only
+ * accesses the timer queue, which has already been initialized.
+ *
+ * This software UART is not completely reliable, but might suit debug output
+ * or communication that has an error detection layer, and it is more reliable
+ * at lower baud rates. While it can run up to 115200 baud it is not very
+ * reliable at these higher rates. It is not uncommon for the MAC timer
+ * handler to be delayed 20us, so at UART baud rates above 19200 errors are
+ * expected. This driver attempts to measure the timing errors and this can be
+ * used to help detect when timing errors have occurred.
+ */
+
+static void IRAM output_handler(void *arg)
+{
+    tsoftuart_t *uart = arg;
+    uint32_t tail = uart->output_queue_tail;
+
+    do {
+        uint32_t state = uart->output_queue_state ^ 1;
+        uint64_t current = mactime_get_count();
+        gpio_write(uart->tx_pin, state);
+        uart->output_queue_state = state;
+
+        if (tail == 0) {
+            // First transition.
+            uart->output_start_time = current;
+            uart->output_expected_time = current;
+        }
+
+        /* The difference can be negative because the delay is skipped
+         * if very short, see below. */
+        int32_t err = current - uart->output_expected_time;
+        if (err > uart->output_queue_error_high) {
+            uart->output_queue_error_high = err;
+        }
+        if (err < uart->output_queue_error_low) {
+            uart->output_queue_error_low = err;
+        }
+        
+        if (tail >= uart->output_queue_head) {
+            // Done.
+            uart->output_queue_tail = tail;
+            uart->output_done = 1;
+            return;
+        }
+
+        /* Offset from the start. */
+        uint32_t next = uart->output_queue[tail++];
+        uint64_t target = uart->output_start_time + next;
+        uart->output_expected_time = target;
+        /* Target an earlier time, that would not give an error if
+         * actually met, to give more room for the response delay. */
+        target -= 4;
+        int64_t diff = target - current;
+        if (diff >= 0) {
+            uart->output_queue_tail = tail;
+            mactime_add_pending(&uart->output_mactimer, target);
+            break;
+        }
+    } while(1);
+}
+
+void tsoftuart_putc(tsoftuart_t *uart, uint8_t ch)
+{
+    uart->output_queue_state = 1;
+    gpio_write(uart->tx_pin, uart->output_queue_state);
+
+    uart->output_queue_head = 0;
+    uart->output_queue_tail = 0;
+
+    uart->output_queue_error_high = 0;
+    uart->output_queue_error_low = 0;
+
+    uart->output_done = 0;
+    
+    uint32_t state = 0;
+    uint32_t count = 1;
+    size_t head = 0;
+    uint32_t cumulative = 0;
+    uint32_t td = uart->td;
+
+
+    for (size_t i = 0; i < 8; i++) {
+        if ((ch & 1) == state) {
+            /* No change */
+            count++;
+        } else {
+            cumulative += count * td;
+            uart->output_queue[head++] = (cumulative + 128) >> 8;
+            state ^= 1;
+            count = 1;
+        }
+        ch >>= 1;
+    }
+
+    if (state == 0) {
+        cumulative += count * td;
+        uart->output_queue[head++] = (cumulative + 128) >> 8;
+        state ^= 1;
+        count = 1;
+    }
+
+    uart->output_queue_head = head;
+
+    /* Trigger the first transition in the future. */
+    mactimer_arm(&uart->output_mactimer, 20);
+
+    /* Wait until the transmittions is expected to have completed. */
+    uint32_t delay = (td * 11 + 128) >> 8;
+    vTaskDelay(((delay / 1000) + portTICK_PERIOD_MS) / portTICK_PERIOD_MS);
+
+    /* Double check that it is done. There is a possibility that the timer has
+     * failed to trigger, and this needed to be detected and the timer removed
+     * from the pending list before retrying. */
+    size_t i;
+    for (i = 0; uart->output_done == 0 && i < 10; i++) {
+        vTaskDelay(1);
+    }
+
+    if (uart->output_done == 0) {
+        /* Remove the timer. */
+        mactimer_disarm(&uart->output_mactimer);
+        /* Set the output high */
+        gpio_write(uart->tx_pin, 1);
+    }
+}
+
+ssize_t tsoftuart_write(tsoftuart_t *uart, const void *ptr, size_t len)
+{
+    for(int i = 0; i < len; i++) {
+        tsoftuart_putc(uart, ((char *)ptr)[i]);
+    }
+    return len;
+}
+
+tsoftuart_t *tsoftuart_init(uint8_t tx_pin, uint32_t baud_rate)
+{
+    tsoftuart_t *uart = malloc(sizeof(tsoftuart_t));
+
+    if (uart) {
+        uart->tx_pin = tx_pin;
+        uart->td = 256000000 / baud_rate;
+        gpio_enable(tx_pin, GPIO_OUTPUT);
+        gpio_set_pullup(tx_pin, true, false);
+        gpio_write(tx_pin, 1);
+        mactimer_init();
+        mactimer_setfn(&uart->output_mactimer, output_handler, uart);
+    }
+
+    return uart;
+}
+

extras/tsoftuart/tsoftuart.h

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+/*
+ * Software timer based UART driver.
+ *
+ * Copyright (C) 2018 to 2019 OurAirQuality.org
+ *
+ * Licensed under the Apache License, Version 2.0, January 2004 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *      http://www.apache.org/licenses/
+ *
+ * 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 CONTRIBUTORS 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 WITH THE SOFTWARE.
+ *
+ */
+
+#ifndef _TSOFTUART_H
+#define _TSOFTUART_H
+
+#include "mactimer/mactimer.h"
+
+typedef struct tsoftuart {
+    uint32_t tx_pin;
+    /* Bit time period in usec * 256 */
+    uint32_t td;
+    mactimer_t output_mactimer;
+    uint32_t output_queue[16];
+    volatile uint64_t output_start_time;
+    volatile size_t output_queue_head;
+    volatile size_t output_queue_tail;
+    size_t output_queue_state;
+    uint64_t output_expected_time;
+    int32_t output_queue_error_high;
+    int32_t output_queue_error_low;
+    uint32_t output_done;
+} tsoftuart_t;
+
+void tsoftuart_putc(tsoftuart_t *uart, uint8_t ch);
+ssize_t tsoftuart_write(tsoftuart_t *uart, const void *ptr, size_t len);
+tsoftuart_t *tsoftuart_init(uint8_t tx_pin, uint32_t baud_rate);
+
+#endif /* _TSOFTUART_H */