Add I2C slave support and include a simple example

Also fix the initial pins for the 2nd I2C interface onboard.

libraries/Wire/Wire.cpp

@@ -24,6 +24,8 @@
 #include <Arduino.h>
 #include <hardware/gpio.h>
 #include <hardware/i2c.h>
+#include <hardware/irq.h>
+#include <hardware/regs/intctrl.h>
 #include "Wire.h"
 
 TwoWire::TwoWire(i2c_inst_t *i2c, pin_size_t sda, pin_size_t scl) {
@@ -85,11 +87,16 @@ void TwoWire::begin() {
     _buffLen = 0;
 }
 
+static void _handler0() {
+    Wire.onIRQ();
+}
+
+static void _handler1() {
+    Wire1.onIRQ();
+}
+
 // Slave mode
 void TwoWire::begin(uint8_t addr) {
-    // Slave mode isn't documented in the SDK, need to twiddle raw registers
-    // and use bare interrupts.  TODO to implement, for now.
-#if 0
     if (_running) {
         // ERROR
         return;
@@ -97,11 +104,54 @@ void TwoWire::begin(uint8_t addr) {
     _slave = true;
     i2c_init(_i2c, _clkHz);
     i2c_set_slave_mode(_i2c, true, addr);
+
+    // Our callback IRQ
+    _i2c->hw->intr_mask = (1<<10) | (1<<9) | (1<<5)| (1<<2);
+
+    int irqNo = I2C0_IRQ + i2c_hw_index(_i2c);
+    irq_set_exclusive_handler(irqNo, i2c_hw_index(_i2c) == 0 ? _handler0 : _handler1);
+    irq_set_enabled(irqNo, true);
+
+
     gpio_set_function(_sda, GPIO_FUNC_I2C);
     gpio_pull_up(_sda);
     gpio_set_function(_scl, GPIO_FUNC_I2C);
     gpio_pull_up(_scl);
-#endif
+
+    _running = true;
+}
+
+void TwoWire::onIRQ() {
+    if (_i2c->hw->intr_stat & (1<<10)) {
+        _buffLen = 0;
+        _buffOff = 0;
+        _slaveStartDet = true;
+        _i2c->hw->clr_start_det;
+    }
+    if (_i2c->hw->intr_stat & (1<<9)) {
+        if (_onReceiveCallback) {
+            _onReceiveCallback(_buffLen);
+        }
+        _buffLen = 0;
+         _buffOff = 0;
+        _slaveStartDet = false;
+        _i2c->hw->clr_stop_det;
+    }
+    if (_i2c->hw->intr_stat & (1<<5)) {
+        // RD_REQ
+        if (_onRequestCallback) {
+            _onRequestCallback();
+        }
+        _i2c->hw->clr_rd_req;
+    }
+    if (_i2c->hw->intr_stat & (1<<2)) {
+        // RX_FULL
+        if (_slaveStartDet && (_buffLen < sizeof(_buff))) {
+            _buff[_buffLen++] = _i2c->hw->data_cmd & 0xff;
+        } else {
+            _i2c->hw->data_cmd;
+        }
+    }
 }
 
 void TwoWire::end() {
@@ -161,11 +211,22 @@ uint8_t TwoWire::endTransmission() {
 }
 
 size_t TwoWire::write(uint8_t ucData) {
-    if (!_running || !_txBegun || (_buffLen == sizeof(_buff))) {
+    if (!_running) {
         return 0;
     }
-    _buff[_buffLen++] = ucData;
-    return 1 ;
+
+    if (_slave) {
+        // Wait for a spot in the TX FIFO
+        while (0 == _i2c->hw->status & (1<<1)) { /* noop wait */ }
+        _i2c->hw->data_cmd = ucData;
+        return 1;
+    } else {
+        if (!_txBegun || (_buffLen == sizeof(_buff))) {
+            return 0;
+        }
+        _buff[_buffLen++] = ucData;
+        return 1 ;
+    }
 }
 
 size_t TwoWire::write(const uint8_t *data, size_t quantity) {
@@ -213,5 +274,4 @@ void TwoWire::onRequest(void(*function)(void))
 }
 
 TwoWire Wire(i2c0, 0, 1);
-TwoWire Wire1(i2c1, 4, 5);
-
+TwoWire Wire1(i2c1, 2, 3);

libraries/Wire/Wire.h

@@ -75,6 +75,9 @@ public:
     inline size_t write(int n) { return write((uint8_t)n); }
     using Print::write;
 
+    // IRQ callback
+    void onIRQ();
+
 private:
     i2c_inst_t *_i2c;
     pin_size_t _sda;
@@ -94,6 +97,8 @@ private:
     void (*_onRequestCallback)(void);
     void (*_onReceiveCallback)(int);
 
+    bool _slaveStartDet = false;
+
     // TWI clock frequency
     static const uint32_t TWI_CLOCK = 100000;
 };

libraries/Wire/examples/TalkingToMyself/TalkingToMyself.ino

+// Simple I2C master and slave demo - Earle F. Philhower, III
+// Released into the public domain
+// 
+// Using both onboard I2C interfaces, have one master and one slave
+// and send data both ways between them
+//
+// To run, connect GPIO0 to GPIO2, GPIO1 to GPIO3 on a single Pico
+
+#include <Wire.h>
+
+void setup() {
+    Serial.begin(115200);
+    delay(5000);
+    Wire.begin();
+    Wire1.begin(0x30);
+    Wire1.onReceive(recv);
+    Wire1.onRequest(req);
+}
+
+static char buff[100];
+void loop() {
+    static int p;
+    char b[90];
+
+    // Write a value over I2C to the slave
+    Serial.println("Sending...");
+    Wire.beginTransmission(0x30);
+    sprintf(b, "pass %d", p++);
+    Wire.write(b, strlen(b));
+    Wire.endTransmission();
+
+    // Ensure the slave processing is done and print it out
+    delay(1000);
+    Serial.printf("buff: '%s'\r\n", buff);
+
+    // Read from the slave and print out
+    Wire.requestFrom(0x30, 6);
+    Serial.print("\nrecv: '");
+    while(Wire.available()) {
+        Serial.print((char)Wire.read());
+    }
+    Serial.println("'");
+    delay(1000);
+}
+
+// These are called in an **INTERRUPT CONTEXT** which means NO serial port
+// access (i.e. Serial.print is illegal) and no memory allocations, etc.
+
+// Called when the I2C slave gets written to
+void recv(int len) {
+    int i;
+    // Just stuff the sent bytes into a global the main routine can pick up and use
+    for (i=0; i<len; i++) buff[i] = Wire1.read();
+    buff[i] = 0;
+}
+
+// Called when the I2C slave is read from
+void req() {
+    static int ctr = 765;
+    char buff[7];
+    // Return a simple incrementing hex value
+    sprintf(buff, "%06X", (ctr++) % 65535);
+    Wire1.write(buff, 6);
+}