diff --git a/core/newlib_syscalls.c b/core/newlib_syscalls.c
index ae15aff..b414481 100644
--- a/core/newlib_syscalls.c
+++ b/core/newlib_syscalls.c
@@ -52,7 +52,7 @@ long _write_r(struct _reent *r, int fd, const char *ptr, int len )
}
/* syscall implementation for stdio read from UART */
-long _read_r( struct _reent *r, int fd, char *ptr, int len )
+__attribute__((weak)) long _read_r( struct _reent *r, int fd, char *ptr, int len )
{
int ch, i;
diff --git a/examples/terminal/FreeRTOSConfig.h b/examples/terminal/FreeRTOSConfig.h
new file mode 100644
index 0000000..0a9a6b7
--- /dev/null
+++ b/examples/terminal/FreeRTOSConfig.h
@@ -0,0 +1,12 @@
+/* Terminal FreeRTOSConfig overrides.
+
+ This is intended as an example of overriding some of the default FreeRTOSConfig settings,
+ which are otherwise found in FreeRTOS/Source/include/FreeRTOSConfig.h
+*/
+
+/* The serial driver depends on counting semaphores */
+#define configUSE_COUNTING_SEMAPHORES 1
+
+/* Use the defaults for everything else */
+#include_next<FreeRTOSConfig.h>
+
diff --git a/examples/terminal/Makefile b/examples/terminal/Makefile
new file mode 100644
index 0000000..f3c8bad
--- /dev/null
+++ b/examples/terminal/Makefile
@@ -0,0 +1,3 @@
+PROGRAM=terminal
+EXTRA_COMPONENTS=extras/stdin_uart_interrupt
+include ../../common.mk
diff --git a/examples/terminal/terminal.c b/examples/terminal/terminal.c
new file mode 100644
index 0000000..f7c5923
--- /dev/null
+++ b/examples/terminal/terminal.c
@@ -0,0 +1,117 @@
+/* Serial terminal example
+ * UART RX is interrupt driven
+ * Implements a simple GPIO terminal for setting and clearing GPIOs
+ *
+ * This sample code is in the public domain.
+ */
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <string.h>
+#include <esp8266.h>
+#include <esp/uart.h>
+#include "FreeRTOS.h"
+#include "task.h"
+
+#define MAX_ARGC (10)
+#define BUFFER_SIZE (81)
+
+static void cmd_on(uint32_t argc, char *argv[])
+{
+ if (argc >= 2) {
+ for(int i=1; i<argc; i++) {
+ uint8_t gpio_num = atoi(argv[i]);
+ gpio_enable(gpio_num, GPIO_OUTPUT);
+ gpio_write(gpio_num, true);
+ printf("On %d\n", gpio_num);
+ }
+ } else {
+ printf("Error: missing gpio number.\n");
+ }
+}
+
+static void cmd_off(uint32_t argc, char *argv[])
+{
+ if (argc >= 2) {
+ for(int i=1; i<argc; i++) {
+ uint8_t gpio_num = atoi(argv[i]);
+ gpio_enable(gpio_num, GPIO_OUTPUT);
+ gpio_write(gpio_num, false);
+ printf("Off %d\n", gpio_num);
+ }
+ } else {
+ printf("Error: missing gpio number.\n");
+ }
+}
+
+static void cmd_help(uint32_t argc, char *argv[])
+{
+ printf("on <gpio number> [ <gpio number>]+ Set gpio to 1\n");
+ printf("off <gpio number> [ <gpio number>]+ Set gpio to 0\n");
+ printf("sleep Take a nap\n");
+ printf("\nExample:\n");
+ printf(" on 0<enter> switches on gpio 0\n");
+ printf(" on 0 2 4<enter> switches on gpios 0, 2 and 4\n");
+}
+
+static void cmd_sleep(uint32_t argc, char *argv[])
+{
+ printf("Type away while I take a 2 second nap (ie. let you test the UART HW FIFO\n");
+ vTaskDelay(2000 / portTICK_RATE_MS);
+}
+
+static void handle_command(char *cmd)
+{
+ char *argv[MAX_ARGC];
+ int argc = 1;
+ char *temp, *rover;
+ memset((void*) argv, 0, sizeof(argv));
+ argv[0] = cmd;
+ rover = cmd;
+ // Split string "<command> <argument 1> <argument 2> ... <argument N>"
+ // into argv, argc style
+ while(argc < MAX_ARGC && (temp = strstr(rover, " "))) {
+ rover = &(temp[1]);
+ argv[argc++] = rover;
+ *temp = 0;
+ }
+
+ if (strlen(argv[0]) > 0) {
+ if (strcmp(argv[0], "help") == 0) cmd_help(argc, argv);
+ else if (strcmp(argv[0], "on") == 0) cmd_on(argc, argv);
+ else if (strcmp(argv[0], "off") == 0) cmd_off(argc, argv);
+ else if (strcmp(argv[0], "sleep") == 0) cmd_sleep(argc, argv);
+ else printf("Unknown command %s, try 'help'\n", argv[0]);
+ }
+}
+
+static void gpiomon()
+{
+ char ch;
+ char cmd[81];
+ int i = 0;
+ printf("\n\n\nWelcome to gpiomon. Type 'help<enter>' for, well, help\n");
+ printf("%% ");
+ while(1) {
+ if (read(0, (void*)&ch, 1)) { // 0 is stdin
+ printf("%c", ch);
+ if (ch == '\n' || ch == '\r') {
+ cmd[i] = 0;
+ i = 0;
+ printf("\n");
+ handle_command((char*) cmd);
+ printf("%% ");
+ } else {
+ if (i < sizeof(cmd)) cmd[i++] = ch;
+ }
+ }
+ }
+}
+
+void user_init(void)
+{
+ uart_set_baud(0, 115200);
+ setbuf(stdout, NULL);
+ gpiomon();
+}
diff --git a/extras/stdin_uart_interrupt/README.txt b/extras/stdin_uart_interrupt/README.txt
new file mode 100644
index 0000000..35f5fa3
--- /dev/null
+++ b/extras/stdin_uart_interrupt/README.txt
@@ -0,0 +1,11 @@
+This module adds interrupt driven receive on UART 0. Using semaphores, a thread
+calling read(...) when no data is available will block in an RTOS expected
+manner until data arrives.
+
+This allows for a background thread running a serial terminal in your program
+for debugging and state inspection consuming no CPU cycles at all. Not using
+this module will make that thread while(1) until data arrives.
+
+No code changes are needed for adding this module, all you need to do is to add
+it to EXTRA_COMPONENTS and add the directive configUSE_COUNTING_SEMAPHORES from
+FreeRTOSConfig.h in examples/terminal to your project.
\ No newline at end of file
diff --git a/extras/stdin_uart_interrupt/component.mk b/extras/stdin_uart_interrupt/component.mk
new file mode 100644
index 0000000..e00cf81
--- /dev/null
+++ b/extras/stdin_uart_interrupt/component.mk
@@ -0,0 +1,13 @@
+# Component makefile for extras/stdin_uart_interrupt
+#
+# See examples/terminal for usage. Well, actually there is no need to see it
+# for 'usage' as this module is a drop-in replacement for the original polled
+# version of reading from the UART.
+
+INC_DIRS += $(ROOT)extras/stdin_uart_interrupt
+
+# args for passing into compile rule generation
+extras/stdin_uart_interrupt_INC_DIR = $(ROOT)extras/stdin_uart_interrupt
+extras/stdin_uart_interrupt_SRC_DIR = $(ROOT)extras/stdin_uart_interrupt
+
+$(eval $(call component_compile_rules,extras/stdin_uart_interrupt))
diff --git a/extras/stdin_uart_interrupt/stdin_uart_interrupt.c b/extras/stdin_uart_interrupt/stdin_uart_interrupt.c
new file mode 100644
index 0000000..cee7b2f
--- /dev/null
+++ b/extras/stdin_uart_interrupt/stdin_uart_interrupt.c
@@ -0,0 +1,117 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Johan Kanflo (github.com/kanflo)
+ *
+ * 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 <esp8266.h>
+#include <FreeRTOS.h>
+#include <semphr.h>
+
+#if (configUSE_COUNTING_SEMAPHORES == 0)
+ #error "You need to define configUSE_COUNTING_SEMAPHORES in a local FreeRTOSConfig.h, see examples/terminal/FreeRTOSConfig.h"
+#endif
+
+// IRQ driven UART RX driver for ESP8266 written for use with esp-open-rtos
+// TODO: Handle UART1
+
+#ifndef UART0
+#define UART0 (0)
+#endif
+
+#define UART0_RX_SIZE (128) // ESP8266 UART HW FIFO size
+
+static xSemaphoreHandle uart0_sem = NULL;
+static bool inited = false;
+static void uart0_rx_init(void);
+
+IRAM void uart0_rx_handler(void)
+{
+ // TODO: Handle UART1, see reg 0x3ff20020, bit2, bit0 represents uart1 and uart0 respectively
+ if (!UART(UART0).INT_STATUS & UART_INT_STATUS_RXFIFO_FULL) {
+ return;
+ }
+// printf(" [%08x (%d)]\n", READ_PERI_REG(UART_INT_ST(UART0)), READ_PERI_REG(UART_STATUS(UART0)) & (UART_RXFIFO_CNT << UART_RXFIFO_CNT_S));
+ if (UART(UART0).INT_STATUS & UART_INT_STATUS_RXFIFO_FULL) {
+ UART(UART0).INT_CLEAR = UART_INT_CLEAR_RXFIFO_FULL;
+ if (UART(UART0).STATUS & (UART_STATUS_RXFIFO_COUNT_M << UART_STATUS_RXFIFO_COUNT_S)) {
+ long int xHigherPriorityTaskWoken;
+ _xt_isr_mask(1 << INUM_UART);
+ _xt_clear_ints(1<<INUM_UART);
+ xSemaphoreGiveFromISR(uart0_sem, &xHigherPriorityTaskWoken);
+ if(xHigherPriorityTaskWoken) {
+ portYIELD();
+ }
+ }
+ } else {
+ printf("Error: unexpected uart irq, INT_STATUS 0x%02x\n", UART(UART0).INT_STATUS);
+ }
+}
+
+uint32_t uart0_num_char(void)
+{
+ uint32_t count;
+ if (!inited) uart0_rx_init();
+ count = UART(UART0).STATUS & (UART_STATUS_RXFIFO_COUNT_M << UART_STATUS_RXFIFO_COUNT_S);
+ return count;
+}
+
+// _read_r in core/newlib_syscalls.c will be skipped by the linker in favour
+// of this function
+long _read_r(struct _reent *r, int fd, char *ptr, int len)
+{
+ if (!inited) uart0_rx_init();
+ for(int i = 0; i < len; i++) {
+ if (!(UART(UART0).STATUS & (UART_STATUS_RXFIFO_COUNT_M << UART_STATUS_RXFIFO_COUNT_S))) {
+ _xt_isr_unmask(1 << INUM_UART);
+ if (!xSemaphoreTake(uart0_sem, portMAX_DELAY)) {
+ printf("\nFailed to get sem\n");
+ }
+ }
+ ptr[i] = UART(UART0).FIFO & (UART_FIFO_DATA_M << UART_FIFO_DATA_S);
+ }
+ return len;
+}
+
+static void uart0_rx_init(void)
+{
+ int trig_lvl = 1;
+ uart0_sem = xSemaphoreCreateCounting(UART0_RX_SIZE, 0);
+
+ _xt_isr_attach(INUM_UART, uart0_rx_handler);
+ _xt_isr_unmask(1 << INUM_UART);
+
+ // clear rx and tx fifo,not ready
+ uint32_t conf = UART(UART0).CONF0;
+ UART(UART0).CONF0 = conf | UART_CONF0_RXFIFO_RESET | UART_CONF0_TXFIFO_RESET;
+ UART(UART0).CONF0 = conf & ~(UART_CONF0_RXFIFO_RESET | UART_CONF0_TXFIFO_RESET);
+
+ // set rx fifo trigger
+ UART(UART0).CONF1 |= (trig_lvl & UART_CONF1_RXFIFO_FULL_THRESHOLD_M) << UART_CONF1_RXFIFO_FULL_THRESHOLD_S;
+
+ // clear all interrupts
+ UART(UART0).INT_CLEAR = 0x1ff;
+
+ // enable rx_interrupt
+ UART(UART0).INT_ENABLE = UART_INT_ENABLE_RXFIFO_FULL;
+
+ inited = true;
+}
diff --git a/extras/stdin_uart_interrupt/stdin_uart_interrupt.h b/extras/stdin_uart_interrupt/stdin_uart_interrupt.h
new file mode 100644
index 0000000..05652bb
--- /dev/null
+++ b/extras/stdin_uart_interrupt/stdin_uart_interrupt.h
@@ -0,0 +1,32 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Johan Kanflo (github.com/kanflo)
+ *
+ * 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.
+ */
+
+#ifndef __STDIN_UART_INTERRUPT_H__
+#define __STDIN_UART_INTERRUPT_H__
+
+#include <stdint.h>
+
+// Return number of characters waiting in UART0
+uint32_t uart0_num_char(void);
+#endif