diff --git a/build.zig b/build.zig index 54479cb..25d831c 100644 --- a/build.zig +++ b/build.zig @@ -1269,6 +1269,37 @@ const exercises = [_]Exercise{ \\Max difference (new fn): 0.014 , }, + .{ .main_file = "110_quiz9.zig", .output = + \\Toggle pins with XOR on PORTB + \\----------------------------- + \\ 1100 // (initial state of PORTB) + \\^ 0101 // (bitmask) + \\= 1001 + \\ + \\ 1100 // (initial state of PORTB) + \\^ 0011 // (bitmask) + \\= 1111 + \\ + \\Set pins with OR on PORTB + \\------------------------- + \\ 1001 // (initial state of PORTB) + \\| 0100 // (bitmask) + \\= 1101 + \\ + \\ 1001 // (reset state) + \\| 0100 // (bitmask) + \\= 1101 + \\ + \\Clear pins with AND and NOT on PORTB + \\------------------------------------ + \\ 1110 // (initial state of PORTB) + \\& 1011 // (bitmask) + \\= 1010 + \\ + \\ 0111 // (reset state) + \\& 1110 // (bitmask) + \\= 0110 + }, .{ .main_file = "999_the_end.zig", .output = diff --git a/exercises/110_quiz9.zig b/exercises/110_quiz9.zig new file mode 100644 index 0000000..cd0048b --- /dev/null +++ b/exercises/110_quiz9.zig @@ -0,0 +1,484 @@ +// ---------------------------------------------------------------------------- +// Quiz Time: Toggling, Setting, and Clearing Bits +// ---------------------------------------------------------------------------- +// +// Another exciting thing about Zig is its suitability for embedded +// programming. Your Zig code doesn't have to remain on your laptop; you can +// also deploy your code to microcontrollers! This means you can write Zig to +// drive your next robot or greenhouse climate control system! Ready to enter +// the exciting world of embedded programming? Let's get started! +// +// ---------------------------------------------------------------------------- +// Some Background +// ---------------------------------------------------------------------------- +// +// A common activity in microcontroller programming is setting and clearing +// bits on input and output pins. This lets you control LEDs, sensors, motors +// and more! In a previous exercise (097_bit_manipulation.zig) you learned how +// to swap two bytes using the ^ (XOR - exclusive or) operator. This quiz will +// test your knowledge of bit manipulation in Zig while giving you a taste of +// what it's like to control registers in a real microcontroller. Included at +// the end are some helper functions that demonstrate how we might make our +// code a little more readable. +// +// Below is a pinout diagram for the famous ATmega328 AVR microcontroller used +// as the primary microchip on popular microcontroller platforms like the +// Arduino UNO. +// +// ============ PINOUT DIAGRAM FOR ATMEGA328 MICROCONTROLLER ============ +// _____ _____ +// | U | +// (RESET) PC6 --| 1 28 |-- PC5 +// PD0 --| 2 27 |-- PC4 +// PD1 --| 3 26 |-- PC3 +// PD2 --| 4 25 |-- PC2 +// PD3 --| 5 24 |-- PC1 +// PD4 --| 6 23 |-- PC0 +// VCC --| 7 22 |-- GND +// GND --| 8 21 |-- AREF +// |-- PB6 --| 9 20 |-- AVCC +// |-- PB7 --| 10 19 |-- PB5 --| +// | PD5 --| 11 18 |-- PB4 --| +// | PD6 --| 12 17 |-- PB3 --| +// | PD7 --| 13 16 |-- PB2 --| +// |-- PB0 --| 14 15 |-- PB1 --| +// | |___________| | +// \_______________________________/ +// | +// PORTB +// +// Drawing inspiration from this diagram, we'll use the pins for PORTB as our +// mental model for this quiz on bit manipulation. It should be noted that +// in the following problems we are using ordinary variables, one of which we +// have named PORTB, to simulate modifying the bits of real hardware registers. +// But in actual microcontroller code, PORTB would be defined something like +// this: +// pub const PORTB = @as(*volatile u8, @ptrFromInt(0x25)); +// +// This lets the compiler know not to make any optimizations to PORTB so that +// the IO pins are properly mapped to our code. +// +// NOTE : To keep things simple, the following problems are given using type +// u4, so applying the output to PORTB would only affect the lower four pins +// PB0..PB3. Of course, there is nothing to prevent you from swapping the u4 +// with a u8 so you can control all 8 of PORTB's IO pins. + +const std = @import("std"); +const print = std.debug.print; +const testing = std.testing; + +pub fn main() !void { + var PORTB: u4 = 0b0000; // only 4 bits wide for simplicity + + // ------------------------------------------------------------------------ + // Quiz + // ------------------------------------------------------------------------ + + // See if you can solve the following problems. The last two problems throw + // you a bit of a curve ball. Try solving them on your own. If you need + // help, scroll to the bottom of main to see some in depth explanations on + // toggling, setting, and clearing bits in Zig. + + print("Toggle pins with XOR on PORTB\n", .{}); + print("-----------------------------\n", .{}); + PORTB = 0b1100; + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("^ {b:0>4} // (bitmask)\n", .{0b0101}); + PORTB ^= (1 << 1) | (1 << 0); // What's wrong here? + checkAnswer(0b1001, PORTB); + + newline(); + + PORTB = 0b1100; + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("^ {b:0>4} // (bitmask)\n", .{0b0011}); + PORTB ^= (1 << 1) & (1 << 0); // What's wrong here? + checkAnswer(0b1111, PORTB); + + newline(); + + print("Set pins with OR on PORTB\n", .{}); + print("-------------------------\n", .{}); + + PORTB = 0b1001; // reset PORTB + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("| {b:0>4} // (bitmask)\n", .{0b0100}); + PORTB = PORTB ??? (1 << 2); // What's missing here? + checkAnswer(0b1101, PORTB); + + newline(); + + PORTB = 0b1001; // reset PORTB + print(" {b:0>4} // (reset state)\n", .{PORTB}); + print("| {b:0>4} // (bitmask)\n", .{0b0100}); + PORTB ??? (1 << 2); // What's missing here? + checkAnswer(0b1101, PORTB); + + newline(); + + print("Clear pins with AND and NOT on PORTB\n", .{}); + print("------------------------------------\n", .{}); + + PORTB = 0b1110; // reset PORTB + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("& {b:0>4} // (bitmask)\n", .{0b1011}); + PORTB = PORTB & ???@as(u4, 1 << 2); // What character is missing here? + checkAnswer(0b1010, PORTB); + + newline(); + + PORTB = 0b0111; // reset PORTB + print(" {b:0>4} // (reset state)\n", .{PORTB}); + print("& {b:0>4} // (bitmask)\n", .{0b1110}); + PORTB &= ~(1 << 0); // What's missing here? + checkAnswer(0b0110, PORTB); + + newline(); + newline(); +} + +// ************************************************************************ +// IN-DEPTH EXPLANATIONS BELOW +// ************************************************************************ +// +// +// +// +// +// +// +// +// +// +// +// ------------------------------------------------------------------------ +// Toggling bits with XOR: +// ------------------------------------------------------------------------ +// XOR stands for "exclusive or". We can toggle bits with the ^ (XOR) +// bitwise operator, like so: +// +// +// In order to output a 1, the logic of an XOR operation requires that the +// two input bits are of different values. Therefore, 0 ^ 1 and 1 ^ 0 will +// both yield a 1 but 0 ^ 0 and 1 ^ 1 will output 0. XOR's unique behavior +// of outputing a 0 when both inputs are 1s is what makes it different from +// the OR operator; it also gives us the ability to toggle bits by putting +// 1s into our bitmask. +// +// - 1s in our bitmask operand, can be thought of as causing the +// corresponding bits in the other operand to flip to the opposite value. +// - 0s cause no change. +// +// The 0s in our bitmask preserve these values +// -XOR op- ---expanded--- in the output. +// _______________/ +// / / +// 1100 1 1 0 0 +// ^ 0101 0 1 0 1 (bitmask) +// ------ - - - - +// = 1001 1 0 0 1 <- This bit was already cleared. +// \_______\ +// \ +// We can think of these bits having flipped +// because of the presence of 1s in those columns +// of our bitmask. +// +// Now let's take a look at setting bits with the | operator. +// +// +// +// +// +// ------------------------------------------------------------------------ +// Setting bits with OR: +// ------------------------------------------------------------------------ +// We can set bits on PORTB with the | (OR) operator, like so: +// +// var PORTB: u4 = 0b1001; +// PORTB = PORTB | 0b0010; +// print("PORTB: {b:0>4}\n", .{PORTB}); // output: 1011 +// +// -OR op- ---expanded--- +// _ Set only this bit. +// / +// 1001 1 0 0 1 +// | 0010 0 0 1 0 (bitmask) +// ------ - - - - +// = 1011 1 0 1 1 +// \___\_______\ +// \ +// These bits remain untouched because OR-ing with +// a 0 effects no change. +// +// ------------------------------------------------------------------------ +// To create a bitmask like 0b0010 used above: +// +// 1. First, shift the value 1 over one place with the bitwise << (shift +// left) operator as indicated below: +// 1 << 0 -> 0001 +// 1 << 1 -> 0010 <-- Shift 1 one place to the left +// 1 << 2 -> 0100 +// 1 << 3 -> 1000 +// +// This allows us to rewrite the above code like this: +// +// var PORTB: u4 = 0b1001; +// PORTB = PORTB | (1 << 1); +// print("PORTB: {b:0>4}\n", .{PORTB}); // output: 1011 +// +// Finally, as in the C language, Zig allows us to use the |= operator, so +// we can rewrite our code again in an even more compact and idiomatic +// form: PORTB |= (1 << 1) + +// So now we've covered how to toggle and set bits. What about clearing +// them? Well, this is where Zig throws us a curve ball. Don't worry we'll +// go through it step by step. +// +// +// +// +// +// ------------------------------------------------------------------------ +// Clearing bits with AND and NOT: +// ------------------------------------------------------------------------ +// We can clear bits with the & (AND) bitwise operator, like so: + +// PORTB = 0b1110; // reset PORTB +// PORTB = PORTB & 0b1011; +// print("PORTB: {b:0>4}\n", .{PORTB}); // output -> 1010 +// +// - 0s clear bits when used in conjuction with a bitwise AND. +// - 1s do nothing, thus preserving the original bits. +// +// -AND op- ---expanded--- +// __________ Clear only this bit. +// / +// 1110 1 1 1 0 +// & 1011 1 0 1 1 (bitmask) +// ------ - - - - +// = 1010 1 0 1 0 <- This bit was already cleared. +// \_______\ +// \ +// These bits remain untouched because AND-ing with a +// 1 preserves the original bit value whether 0 or 1. +// +// ------------------------------------------------------------------------ +// We can use the ~ (NOT) operator to easily create a bitmask like 1011: +// +// 1. First, shift the value 1 over two places with the bit-wise << (shift +// left) operator as indicated below: +// 1 << 0 -> 0001 +// 1 << 1 -> 0010 +// 1 << 2 -> 0100 <- The 1 has been shifted two places to the left +// 1 << 3 -> 1000 +// +// 2. The second step in creating our bitmask is to invert the bits +// ~0100 -> 1011 +// in C we would write this as: +// ~(1 << 2) -> 1011 +// +// But if we try to compile ~(1 << 2) in Zig, we'll get an error: +// unable to perform binary not operation on type 'comptime_int' +// +// Before Zig can invert our bits, it needs to know the number of +// bits it's being asked to invert. +// +// We do this with the @as (cast as) built-in like this: +// @as(u4, 1 << 2) -> 0100 +// +// Finally, we can invert our new mask by placing the NOT ~ operator +// before our expression, like this: +// ~@as(u4, 1 << 2) -> 1011 +// +// If you are offput by the fact that you can't simply invert bits like +// you can in languages such as C without casting to a particular size +// of integer, you're not alone. However, this is actually another +// instance where Zig is really helpful because it protects you from +// difficult to debug integer overflow bugs that can have you tearing +// your hair out. In the interest of keeping things sane, Zig requires +// you simply to tell it the size of number you are inverting. In the +// words of Andrew Kelley, "If you want to invert the bits of an +// integer, zig has to know how many bits there are." +// +// For more insight into the Zig team's position on why the language +// takes the approach it does with the ~ operator, take a look at +// Andrew's comments on the following github issue: +// https://github.com/ziglang/zig/issues/1382#issuecomment-414459529 +// +// Whew, so after all that what we end up with is: +// PORTB = PORTB & ~@as(u4, 1 << 2); +// +// We can shorten this with the &= combined AND and assignment operator, +// which applies the AND operator on PORTB and then reassigns PORTB. Here's +// what that looks like: +// PORTB &= ~@as(u4, 1 << 2); +// + +// ------------------------------------------------------------------------ +// Conclusion +// ------------------------------------------------------------------------ +// +// While the examples in this quiz have used only 4-bit wide variables, +// working with 8 bits is no different. Here's an example where we set +// every other bit beginning with the two's place: + +// var PORTD: u8 = 0b0000_0000; +// print("PORTD: {b:0>8}\n", .{PORTD}); +// PORTD |= (1 << 1); +// PORTD = setBit(u8, PORTD, 3); +// PORTD |= (1 << 5) | (1 << 7); +// print("PORTD: {b:0>8} // set every other bit\n", .{PORTD}); +// PORTD = ~PORTD; +// print("PORTD: {b:0>8} // bits flipped with NOT (~)\n", .{PORTD}); +// newline(); +// +// // Here we clear every other bit beginning with the two's place. +// +// PORTD = 0b1111_1111; +// print("PORTD: {b:0>8}\n", .{PORTD}); +// PORTD &= ~@as(u8, 1 << 1); +// PORTD = clearBit(u8, PORTD, 3); +// PORTD &= ~@as(u8, (1 << 5) | (1 << 7)); +// print("PORTD: {b:0>8} // clear every other bit\n", .{PORTD}); +// PORTD = ~PORTD; +// print("PORTD: {b:0>8} // bits flipped with NOT (~)\n", .{PORTD}); +// newline(); + +// ---------------------------------------------------------------------------- +// Here are some helper functions for manipulating bits +// ---------------------------------------------------------------------------- + +// Functions for setting, clearing, and toggling a single bit +fn setBit(comptime T: type, byte: T, comptime bit_pos: T) !T { + return byte | (1 << bit_pos); +} + +test "setBit" { + try testing.expectEqual(setBit(u8, 0b0000_0000, 3), 0b0000_1000); +} + +fn clearBit(comptime T: type, byte: T, comptime bit_pos: T) T { + return byte & ~@as(T, (1 << bit_pos)); +} + +test "clearBit" { + try testing.expectEqual(clearBit(u8, 0b1111_1111, 0), 0b1111_1110); +} + +fn toggleBit(comptime T: type, byte: T, comptime bit_pos: T) T { + return byte ^ (1 << bit_pos); +} + +test "toggleBit" { + var byte = toggleBit(u8, 0b0000_0000, 0); + try testing.expectEqual(byte, 0b0000_0001); + byte = toggleBit(u8, byte, 0); + try testing.expectEqual(byte, 0b0000_0000); +} + +// ---------------------------------------------------------------------------- +// Some additional functions for setting, clearing, and toggling multiple bits +// at once with a tuple because, hey, why not? +// ---------------------------------------------------------------------------- +// + +fn createBitmask(comptime T: type, comptime bits: anytype) !T { + comptime var bitmask: T = 0; + inline for (bits) |bit| { + if (bit >= @bitSizeOf(T)) return error.BitPosTooLarge; + if (bit < 0) return error.BitPosTooSmall; + + bitmask |= (1 << bit); + } + return bitmask; +} + +test "creating bitmasks from a tuple" { + try testing.expectEqual(createBitmask(u8, .{0}), 0b0000_0001); + try testing.expectEqual(createBitmask(u8, .{1}), 0b0000_0010); + try testing.expectEqual(createBitmask(u8, .{2}), 0b0000_0100); + try testing.expectEqual(createBitmask(u8, .{3}), 0b0000_1000); + // + try testing.expectEqual(createBitmask(u8, .{ 0, 4 }), 0b0001_0001); + try testing.expectEqual(createBitmask(u8, .{ 1, 5 }), 0b0010_0010); + try testing.expectEqual(createBitmask(u8, .{ 2, 6 }), 0b0100_0100); + try testing.expectEqual(createBitmask(u8, .{ 3, 7 }), 0b1000_1000); + + try testing.expectError(error.BitPosTooLarge, createBitmask(u4, .{4})); +} + +fn setBits(byte: u8, bits: anytype) !u8 { + const bitmask = try createBitmask(u8, bits); + return byte | bitmask; +} + +test "setBits" { + try testing.expectEqual(setBits(0b0000_0000, .{0}), 0b0000_0001); + try testing.expectEqual(setBits(0b0000_0000, .{7}), 0b1000_0000); + + try testing.expectEqual(setBits(0b0000_0000, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_1111); + try testing.expectEqual(setBits(0b1111_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_1111); + + try testing.expectEqual(setBits(0b0000_0000, .{ 2, 3, 4, 5 }), 0b0011_1100); + + try testing.expectError(error.BitPosTooLarge, setBits(0b1111_1111, .{8})); + try testing.expectError(error.BitPosTooSmall, setBits(0b1111_1111, .{-1})); +} + +fn clearBits(comptime byte: u8, comptime bits: anytype) !u8 { + const bitmask: u8 = try createBitmask(u8, bits); + return byte & ~@as(u8, bitmask); +} + +test "clearBits" { + try testing.expectEqual(clearBits(0b1111_1111, .{0}), 0b1111_1110); + try testing.expectEqual(clearBits(0b1111_1111, .{7}), 0b0111_1111); + + try testing.expectEqual(clearBits(0b1111_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b000_0000); + try testing.expectEqual(clearBits(0b0000_0000, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b000_0000); + + try testing.expectEqual(clearBits(0b1111_1111, .{ 0, 1, 6, 7 }), 0b0011_1100); + + try testing.expectError(error.BitPosTooLarge, clearBits(0b1111_1111, .{8})); + try testing.expectError(error.BitPosTooSmall, clearBits(0b1111_1111, .{-1})); +} + +fn toggleBits(comptime byte: u8, comptime bits: anytype) !u8 { + const bitmask = try createBitmask(u8, bits); + return byte ^ bitmask; +} + +test "toggleBits" { + try testing.expectEqual(toggleBits(0b0000_0000, .{0}), 0b0000_0001); + try testing.expectEqual(toggleBits(0b0000_0000, .{7}), 0b1000_0000); + + try testing.expectEqual(toggleBits(0b1111_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b000_0000); + try testing.expectEqual(toggleBits(0b0000_0000, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_1111); + + try testing.expectEqual(toggleBits(0b0000_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_0000); + try testing.expectEqual(toggleBits(0b0000_1111, .{ 0, 1, 2, 3 }), 0b0000_0000); + + try testing.expectEqual(toggleBits(0b0000_0000, .{ 0, 2, 4, 6 }), 0b0101_0101); + + try testing.expectError(error.BitPosTooLarge, toggleBits(0b1111_1111, .{8})); + try testing.expectError(error.BitPosTooSmall, toggleBits(0b1111_1111, .{-1})); +} + +// ---------------------------------------------------------------------------- +// Utility functions +// ---------------------------------------------------------------------------- + +fn newline() void { + print("\n", .{}); +} + +fn checkAnswer(expected: u4, answer: u4) void { + if (expected != answer) { + print("*************************************************************\n", .{}); + print("= {b:0>4} <- INCORRECT! THE EXPECTED OUTPUT IS {b:0>4}\n", .{ answer, expected }); + print("*************************************************************\n", .{}); + } else { + print("= {b:0>4}", .{answer}); + } + newline(); +} diff --git a/patches/patches/110_quiz9.patch b/patches/patches/110_quiz9.patch new file mode 100644 index 0000000..9d9b864 --- /dev/null +++ b/patches/patches/110_quiz9.patch @@ -0,0 +1,56 @@ +--- exercises/110_quiz9.zig 2025-02-08 13:19:48.522641785 -0800 ++++ answers/110_quiz9.zig 2025-02-10 17:42:04.525004335 -0800 +@@ -108,7 +108,7 @@ + PORTB = 0b1100; + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("^ {b:0>4} // (bitmask)\n", .{0b0101}); +- PORTB ^= (1 << 1) | (1 << 0); // What's wrong here? ++ PORTB ^= (1 << 2) | (1 << 0); + checkAnswer(0b1001, PORTB); + + newline(); +@@ -116,7 +116,7 @@ + PORTB = 0b1100; + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("^ {b:0>4} // (bitmask)\n", .{0b0011}); +- PORTB ^= (1 << 1) & (1 << 0); // What's wrong here? ++ PORTB ^= (1 << 1) | (1 << 0); + checkAnswer(0b1111, PORTB); + + newline(); +@@ -170,7 +170,7 @@ + PORTB = 0b1001; // reset PORTB + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("| {b:0>4} // (bitmask)\n", .{0b0100}); +- PORTB = PORTB ??? (1 << 2); // What's missing here? ++ PORTB = PORTB | (1 << 2); + checkAnswer(0b1101, PORTB); + + newline(); +@@ -178,7 +178,7 @@ + PORTB = 0b1001; // reset PORTB + print(" {b:0>4} // (reset state)\n", .{PORTB}); + print("| {b:0>4} // (bitmask)\n", .{0b0100}); +- PORTB ??? (1 << 2); // What's missing here? ++ PORTB |= (1 << 2); + checkAnswer(0b1101, PORTB); + + newline(); +@@ -269,7 +269,7 @@ + PORTB = 0b1110; // reset PORTB + print(" {b:0>4} // (initial state of PORTB)\n", .{PORTB}); + print("& {b:0>4} // (bitmask)\n", .{0b1011}); +- PORTB = PORTB & ???@as(u4, 1 << 2); // What character is missing here? ++ PORTB = PORTB & ~@as(u4, 1 << 2); + checkAnswer(0b1010, PORTB); + + newline(); +@@ -277,7 +277,7 @@ + PORTB = 0b0111; // reset PORTB + print(" {b:0>4} // (reset state)\n", .{PORTB}); + print("& {b:0>4} // (bitmask)\n", .{0b1110}); +- PORTB &= ~(1 << 0); // What's missing here? ++ PORTB &= ~@as(u4, 1 << 0); + checkAnswer(0b0110, PORTB); + + newline();