example: i2c-usb-bridge: Initial support

This application bridges data to and from the serial console to the
I2C bus.
This allows a PC to communicate with an I2C device via a USB port.

On a PC you can connect to the UART of the device running this
application to access the I2C bus. The Tock device will then act as
a I2C master to interact with I2C devices.

Signed-off-by: Alistair Francis <[email protected]>

examples/i2c-usb-bridge/Makefile

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+# Makefile for user application
+
+# Specify this directory relative to the current application.
+TOCK_USERLAND_BASE_DIR = ../..
+
+# Which files to compile.
+C_SRCS := $(wildcard *.c)
+
+# Include userland master makefile. Contains rules and flags for actually
+# building the application.
+include $(TOCK_USERLAND_BASE_DIR)/AppMakefile.mk

examples/i2c-usb-bridge/README.md

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+I2C USB Bridge
+==============
+
+This application bridges data to and from the serial console to the I2C bus.
+This allows a PC to communicate with an I2C device via a USB port.
+
+On a PC you can connect to the UART of the device running this application to
+access the I2C bus. The Tock device will then act as a I2C master to interact
+with I2C devices.
+
+-----------------------       ---------------------------       ----------
+|              |      |  USB  |     Tock       |  I2C   |  I2C  |  I2C   |
+|  PC (Linux)  | UART | <---> | I2C USB Bridge | Master | <---> | Device |
+|              |      |       |                |        |       |        |
+-----------------------       ---------------------------       ----------
+
+Command Format
+--------------
+
+The command format is designed to match the
+[I2C Driver](https://i2cdriver.com/i2cdriver.pdf) format.
+
+The format is as follows
+
+```
+    <r|w> <addr> <len> <data>
+```
+
+For example to read two bytes from address `0x23`
+
+```
+    r 0x23 2
+```
+
+To write `0x12, 0x56` to address `0x23`
+
+```
+    w 0x23 2 0x12,0x56
+```

examples/i2c-usb-bridge/main.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <console.h>
+#include <i2c_master.h>
+
+#define DATA_LEN 64
+
+char command_buf[DATA_LEN];
+uint8_t recieve_buf[DATA_LEN];
+uint8_t send_buf[DATA_LEN];
+
+static int get_command(void) {
+  int idx = 0;
+  memset(command_buf, 0, DATA_LEN);
+
+  // Read in characters until a new line
+  while (1) {
+    int c = getch();
+
+    if (c == RETURNCODE_FAIL) {
+      printf("getch() failed!\n");
+
+      return c;
+    } else {
+      putnstr((char*) &c, 1);
+
+      if (c == '\n' || c == '\r') {
+        return 0;
+      } else {
+        // If this is a valid number record it
+        command_buf[idx] = c;
+        idx += 1;
+
+        // If our buffer is full, quit
+        if (idx >= DATA_LEN) {
+          return 0;
+        }
+      }
+    }
+  }
+}
+
+static void read_data(char *command) {
+  char *op_string, *addr_string, *len_string;
+  long address, len;
+  int i;
+
+  op_string = strtok(command, " ");
+  if (op_string == NULL) {
+    printf("Unable to determine operation\n");
+    return;
+  }
+
+  addr_string = strtok(NULL, " ");
+  if (addr_string == NULL) {
+    printf("Unable to determine address\n");
+    return;
+  }
+
+  len_string = strtok(NULL, " ");
+  if (len_string == NULL) {
+    printf("Unable to determine length\n");
+    return;
+  }
+
+  address = strtol(addr_string, NULL, 16);
+  len     = strtol(len_string, NULL, 16);
+
+  printf("Reading %ld bytes from 0x%lx\n", len, address);
+
+  i2c_master_read_sync(address, recieve_buf, len);
+
+  for (i = 0; i < len; i++) {
+    printf("%c ", recieve_buf[i]);
+  }
+
+  printf("Application Operation complete\n");
+}
+
+static void write_data(char *command) {
+  char *op_string, *addr_string, *len_string;
+  long address, len;
+  int i;
+
+  op_string = strtok(command, " ");
+  if (op_string == NULL) {
+    printf("Unable to determine operation\n");
+    return;
+  }
+
+  addr_string = strtok(NULL, " ");
+  if (addr_string == NULL) {
+    printf("Unable to determine address\n");
+    return;
+  }
+
+  len_string = strtok(NULL, " ");
+  if (len_string == NULL) {
+    printf("Unable to determine length\n");
+    return;
+  }
+
+  address = strtol(addr_string, NULL, 16);
+  len     = strtol(len_string, NULL, 16);
+
+  if (len > DATA_LEN) {
+    printf("The data is larger then the maximum buffer size\n");
+    return;
+  }
+
+  printf("Writing %ld bytes to 0x%lx\n", len, address);
+
+  for (i = 0; i < len; i++) {
+    char *byte = strtok(NULL, ",");
+
+    if (byte == NULL) {
+      printf("Not enough data supplied\n");
+      return;
+    }
+
+    long value = strtol(byte, NULL, 16);
+
+    send_buf[i] = value;
+  }
+
+  for (i = 0; i < len; i++) {
+    printf("%c ", send_buf[i]);
+  }
+
+  i2c_master_write_sync(address, send_buf, len);
+
+  printf("Application Operation complete\n");
+}
+
+int main(void) {
+  printf("I2C USB Bridge\n");
+
+  while (1) {
+    int ret = get_command();
+
+    if (ret < 0) {
+      printf("Error reading stdin\n");
+      exit(-1);
+    }
+
+    if (strncmp(command_buf, "r", 1) == 0) {
+      read_data(command_buf);
+    } else if (strncmp(command_buf, "w", 1) == 0) {
+      write_data(command_buf);
+    } else {
+      printf("Invalid command: %s\n", command_buf);
+      printf("Check the app README for instructinos\n");
+    }
+  }
+
+  return 0;
+}