From 0d0104f5f900ef03d498b274fd64d125c723f311 Mon Sep 17 00:00:00 2001
From: ThomasDerl <145520479+ThomasDerl@users.noreply.github.com>
Date: Tue, 14 Oct 2025 21:30:24 -0500
Subject: [PATCH] New member task: implement MCP23017 driver and test

---
 src/mcp23017.cpp | 126 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 112 insertions(+), 14 deletions(-)

diff --git a/src/mcp23017.cpp b/src/mcp23017.cpp
index 9cb2515..4bb224e 100644
--- a/src/mcp23017.cpp
+++ b/src/mcp23017.cpp
@@ -1,39 +1,137 @@
 #include "mcp23017.h"
 
-// TODO (optional): Define macros for useful register below:
+// Define macros for useful register below:
+#define IODIRA 0x00
+#define GPIOA  0x12
 
-
-// TODO: Initialize i2cBus member
+// Initialize i2cBus member
 Mcp23017::Mcp23017(int addr) {
-
+    // Record the device address. This will be used in the I2C reads and writes of other functions.
+    addr = addr;
 }
 
 uint8_t Mcp23017::get_dir(int pin) {
-    return 0;
-}
+    // Specify to the MCP that we want to read from the IODIRA register from by 
+    // writing the correct register offset.
+    Wire.beginTransmission(addr);
+    Wire.write(IODIRA); 
+    Wire.endTransmission();
+    
+    // Read ONE byte from the IODIRA register we just specified.
+    Wire.requestFrom(addr, (uint8_t)1);
+    uint8_t iodir_val = Wire.read();
 
+    // Do bitwise arithmetic to figure out what part of the byte corresponds 
+    // to the pin we are looking for.
+    uint8_t pin_value = (iodir_val >> pin) & 0x01;
 
-// TODO: Read from state register
+    // Return the value of the pin.
+    return pin_value;
+}
+
+// Read from state register
 uint8_t Mcp23017::get_state(int pin) {
-    return 0;
+    // This function should do the same thing as get_dir(), except it reads from the 
+    // GPIO register instead of the direction register.
+
+    // Specify to the MCP that we want to read from the GPIOA register by 
+    // writing the correct register offset.
+    Wire.beginTransmission(addr);
+    Wire.write(GPIOA); 
+    Wire.endTransmission();
+    
+    // Read ONE byte from the GPIOA register we just specified.
+    Wire.requestFrom(addr, (uint8_t)1);
+    uint8_t gpio_val = Wire.read();
+
+    // Do bitwise arithmetic to figure out what part of the byte corresponds 
+    // to the pin we are looking for.
+    uint8_t pin_value = (gpio_val >> pin) & 0x01;
+
+    // Return the value of the pin.
+    return pin_value;
 }
 
-// TODO: Write to directions register
+// Write to directions register
 int Mcp23017::set_dir(int pin, uint8_t dir) {
-    return 0;
+    Wire.beginTransmission(addr);
+    Wire.write(IODIRA);
+    Wire.endTransmission();
+
+    Wire.requestFrom(addr, (uint8_t)1);
+    uint8_t iodir_val = Wire.read();
+
+// Read get all 8 bits, then bit mask
+
+    // Find out which value (0 or 1) means "input" and which value means "output".  
+    // --> 0 represents output, 1 represents input.
+    
+    // Remember that all I2C communication is done with bytes, so we can't write to specific bit 
+    // in the register to change its value. Think about what we need to do to preserve the values 
+    // of the other bits of the register.
+   
+    // We will need to use bitwise operations to set a certain bit position to a 0 or a 1.
+    if (dir == 1) {
+        // Set the pin to be an input (1)
+        iodir_val |= (1 << pin);
+    } else {
+        // Set the pin to be an output (0)
+        iodir_val &= ~(1 << pin);
+    }
+    
+    // Write updated value back to IODIRA
+    Wire.beginTransmission(addr);
+    Wire.write(IODIRA);
+    Wire.write(iodir_val);
+    return Wire.endTransmission();
 }
 
 // TODO: Write to state register
 int Mcp23017::set_state(int pin, uint8_t val) {
-    return 0;
+    Wire.beginTransmission(addr);
+    Wire.write(GPIOA);
+    Wire.endTransmission();
+
+    Wire.requestFrom(addr, (uint8_t)1);
+    uint8_t gpio_val = Wire.read();
+
+    if (val == 1) {
+        // Set the pin to be HIGH (1)
+        gpio_val |= (1 << pin); 
+    } else {
+        // Set the pin to be LOW (0)
+        gpio_val &= ~(1 << pin);
+    }
+    
+    // Write updated value back to GPIOA
+    Wire.beginTransmission(addr);
+    Wire.write(GPIOA);
+    Wire.write(gpio_val);
+    return Wire.endTransmission();
 }
 
 
 // Verifies that the device is accessible over I2C and sets pin directions
 int Mcp23017::begin(uint8_t directions[8]) {
-    int rc;
-
-    // TODO: Add device ID check
+    // read and verify the default value of the IODIRA register to confirm 
+    // I2C communication between the microcontroller and the MCP23017
+    Wire.beginTransmission(addr);
+    Wire.write(IODIRA);
+    Wire.endTransmission();
+    Wire.requestFrom(addr, (uint8_t)1);
+    
+    // return a 0 if the initialization is a success 
+    // (default value of IODIRA is read correctly), 1 otherwise.
+    uint8_t iodira_confirm = Wire.read();
+    if (iodira_confirm != 0xFF) {
+        // If the value read from IODIRA is not 0xFF, something went wrong.
+        return 1;
+    }
 
+    // set the direction of each pin on the MCP23017
+    for (int i = 0; i < 8; i++) {
+        set_dir(i, directions[i]);
+    }
+    
     return 0;
 }