added Linux I2C_Detect sample program

Author: bitbank2

linux/README

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+BitBang_I2C Linux support
+-------------------------
+The Linux version will compile a C static library (unlike Arduino C++). If you
+require a C++ interface, you can just change the makefile to compile it as such.
+
+To build the library, just run make.
+The I2C_Detector example is also included for Linux. To build it type:
+> make -f make_sample
+Since this uses the PIGPIO library to access the GPIO pins, it must be run as
+sudo. The numbers used for the SCL and SDA pins are the header pin numbers, not
+the BCM GPIO numbers. For example, to see if a RPI "HAT" EEPROM is present on
+i2c-0, you would run it like this:
+> sudo i2c_detect 27 28
+This creates a software i2c bus on header pins 27/28 (BCM GPIO 0/1). If a HAT
+is present, it will show a device detected at address 0x50.
+

linux/main.c

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+//
+// I2C Detector - scan and identify devices on an I2C bus using the BitBang_I2C library
+// 
+// The purpose of this code is to provide a sample sketch which can serve
+// to detect not only the addresses of I2C devices, but what type of device each one is.
+// So far, I've added the 25 devices I've personally used or found to be reliably detected
+// based on their register contents. I encourage people to do pull requests to add support
+// for more devices to make this code have wider appeal.
+
+// There are plenty of I2C devices which appear at fixed addresses, yet don't have unique
+// "Who_Am_I" registers or other data to reliably identify them. It's certainly possible to
+// write code which initializes these devices and tries to verify their identity. This can
+// potentially damage them and would necessarily increase the code size. I would like to keep
+// the size of this code small enough so that it can be included in many microcontroller 
+// projects where code space is scarce.
+
+// Copyright (c) 2019 BitBank Software, Inc.
+// Written by Larry Bank
+// email: [email protected]
+// Project started 25/02/2019
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// Uses my Bit Bang I2C library. You can find it here:
+// https://github.com/bitbank2/BitBang_I2C
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <BitBang_I2C.h>
+#include <pigpio.h>
+
+#define SHOW_NAME
+#ifdef SHOW_NAME
+const char *szNames[]  = {"Unknown","SSD1306","SH1106","VL53L0X","BMP180", "BMP280","BME280",
+                "MPU-60x0", "MPU-9250", "MCP9808","LSM6DS3", "ADXL345", "ADS1115","MAX44009",
+                "MAG3110", "CCS811", "HTS221", "LPS25H", "LSM9DS1","LM8330", "DS3231", "LIS3DH",
+                "LIS3DSH","INA219","SHT3X","HDC1080","MPU6886","BME680", "AXP202", "AXP192", "24AA02XEXX", 
+                "DS1307", "MPU688X", "FT6236G", "FT6336G", "FT6336U", "FT6436", "BM8563","BNO055"};
+#endif
+
+BBI2C bbi2c;
+
+int main(int argc, char **argv)
+{
+int i, iSDA, iSCL;
+uint8_t map[16];
+int iDevice, iCount;
+
+	if (argc != 3) {
+		printf("Bit Bang I2C detector\nUsage: i2c_detect <SDA_PIN> <SCL_PIN>\n");
+		return 0;
+	}
+
+  iSDA = atoi(argv[1]);
+  iSCL = atoi(argv[2]);
+  memset(&bbi2c, 0, sizeof(bbi2c));
+  bbi2c.bWire = 0; // use bit bang, not wire library
+  bbi2c.iSDA = iSDA;
+  bbi2c.iSCL = iSCL;
+  I2CInit(&bbi2c, 100000L);
+
+  printf("Starting I2C Scan\n");
+  I2CScan(&bbi2c, map); // get bitmap of connected I2C devices
+  if (map[0] == 0xfe) // something is wrong with the I2C bus
+  {
+    printf("I2C pins are not correct or the bus is being pulled low by a bad device; unable to run scan\n");
+  }
+  else
+  {
+    iCount = 0;
+    for (i=1; i<128; i++) // skip address 0 (general call address) since more than 1 device can respond
+    {
+      if (map[i>>3] & (1 << (i & 7))) // device found
+      {
+        iCount++;
+	iDevice = I2CDiscoverDevice(&bbi2c, i);
+        printf("Device found at 0x%02x, type = %s\n", i, szNames[iDevice]);
+      }
+    } // for i
+    printf("%d device(s) found\n", iCount);
+  }
+  return 0;
+}

linux/make_sample

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+CFLAGS=-c -Wall -O2
+LIBS = -lBitBang_I2C -lpigpio
+
+all: i2c_detect
+
+i2c_detect: main.o
+	$(CC) main.o $(LIBS) -o i2c_detect
+
+main.o: main.c
+	$(CC) $(CFLAGS) main.c
+
+clean:
+	rm *.o i2c_detect