Erik -
A software I2C interface which is a drop-in replacement for the regular mbed I2C interface in case you run out of I2C ports
Dependents: Luminocity laser-tag
This is a first version. Doesn't mean more versions will come, mainly means it may be a bit buggy. If it does not work for you: first try exactly the same code with the regular hardware I2C. If that does work, well then I made an error somewhere :D. You can send me a message if you can't figure it out, although without your hardware it generally is hard for me to reproduce.
While basic I2C should work, advanced things like clock stretching and multi-master I2C busses are not supported.
If you find an error and solve it: Send a pull request and I generally will accept it :).
Diff: SoftI2C.cpp
- Revision:
- 0:fee70b6fe0e9
- Child:
- 1:05473196d133
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/SoftI2C.cpp Tue Nov 22 20:45:35 2016 +0000
@@ -0,0 +1,166 @@
+#include "SoftI2C.h"
+
+SoftI2C::SoftI2C(PinName sda, PinName scl) : _sda(sda), _scl(scl) {
+ // Set defaults
+ _sda.mode(PullNone);
+ _scl.mode(PullNone);
+ _sda.input();
+ _scl.input();
+ frequency(100000);
+
+ active = false;
+
+ }
+
+void SoftI2C::frequency(int hz) {
+ delay_us = 1000000 / hz / 4; //delay is a quarter of the total period
+}
+
+int SoftI2C::read(int address, char *data, int length, bool repeated) {
+ start();
+
+ // Write address with LSB to one
+ if (write(address | 0x01) == 0) {
+ return 1;
+ }
+
+ // Read the data
+ for(int i = 0; i<length - 1; i++) {
+ data[i] = read(1);
+ }
+ data[length-1] = read(0);
+
+ if (repeated == false) {
+ stop();
+ }
+ return 0;
+}
+
+int SoftI2C::write(int address, const char *data, int length, bool repeated) {
+ start();
+
+ // Write address with LSB to zero
+ if (write(address & 0xFE) == 0) {
+ return 1;
+ }
+
+ // Write the data
+ for(int i = 0; i<length; i++) {
+ if(write(data[i]) == 0) {
+ return 1;
+ }
+ }
+
+ if (repeated == false) {
+ stop();
+ }
+ return 0;
+}
+
+int SoftI2C::read(int ack) {
+ int retval = 0;
+
+ // Shift the bits out, msb first
+ for (int i = 7; i>=0; i--) {
+ //SCL low
+ _scl.output();
+ _scl.write(0);
+ _sda.input();
+ wait_us(delay_us);
+
+ //read SDA
+ retval |= _sda.read() << i;
+ wait_us(delay_us);
+
+ //SCL high again
+ _scl.input();
+ wait_us(delay_us << 1); //wait two delays
+ }
+
+ // Last cycle to set the ACK
+ _scl.output();
+ _scl.write(0);
+ if ( ack ) {
+ _sda.output();
+ _sda.write(0);
+ } else {
+ _sda.input();
+ }
+ wait_us(delay_us << 1);
+
+ _scl.input();
+ wait_us(delay_us << 1);
+
+
+ return retval;
+}
+
+int SoftI2C::write(int data) {
+ // Shift the bits out, msb first
+ for (int i = 7; i>=0; i--) {
+ //SCL low
+ _scl.output();
+ _scl.write(0);
+ wait_us(delay_us);
+
+ //Change SDA depending on the bit
+ if ( (data >> i) & 0x01 ) {
+ _sda.input();
+ } else {
+ _sda.output();
+ _sda.write(0);
+ }
+ wait_us(delay_us);
+
+ //SCL high again
+ _scl.input();
+ wait_us(delay_us << 1); //wait two delays
+ }
+
+ // Last cycle to get the ACK
+ _scl.output();
+ _scl.write(0);
+ wait_us(delay_us);
+
+ _sda.input();
+ wait_us(delay_us);
+
+ _scl.input();
+ wait_us(delay_us);
+ int retval = ~_sda.read(); //Read the ack
+ wait_us(delay_us);
+
+ return retval;
+}
+
+void SoftI2C::start(void) {
+ if (active) { //if repeated start
+ //Set SDA high, toggle scl
+ _sda.input();
+ _scl.output();
+ _scl.write(0);
+ wait_us(delay_us << 1);
+ _scl.input();
+ wait_us(delay_us << 1);
+ }
+ // Pull SDA low
+ _sda.output();
+ _sda.write(0);
+ wait_us(delay_us);
+ active = true;
+}
+
+void SoftI2C::stop(void) {
+ // Float SDA high
+ _scl.output();
+ _scl.write(0);
+ _sda.output();
+ _sda.write(0);
+ wait_us(delay_us);
+ _scl.input();
+ wait_us(delay_us);
+ _sda.input();
+ wait_us(delay_us);
+
+ active = false;
+}
\ No newline at end of file