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@rstropek
rstropek committed Nov 2, 2024
1 parent 2ccdc1d commit ce3d822
Showing 1 changed file with 95 additions and 31 deletions.
126 changes: 95 additions & 31 deletions hello-embedded/hello-world/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,47 +13,111 @@ fn main() -> ! {
rtt_init_print!();
rprintln!("Hello world!");

// The LED matrix is organized into rows (ROW1 to ROW5) and columns (COL1 to COL5). Each row and column represents
// connections to LEDs in a grid formation, where each intersection can turn on or off an LED by controlling the flow of current.
// In a 5x5 matrix like this, there are 25 LEDs, arranged in rows and columns. Each LED is placed at an intersection of a row and a column.
// By setting a row to a high (positive) voltage and a column to low (grounded), current can flow through the corresponding LED
// in that row and column, causing it to light up.
// (see also Microbit Schematic at https://tech.microbit.org/hardware/schematic/, page 2

// In our example, we will use ROW1 and COL1 to turn on an LED. From the schematics (page 3), we can see that
// ROW1 is connected to Port 0/Pin 21 and COL1 is connected to Port 0/Pin 28.

// Configuration of GPIO happens in the PIN_CNF registers. The data sheet for nRF52833
// (https://docs-be.nordicsemi.com/bundle/ps_nrf52833/attach/nRF52833_PS_v1.7.pdf?_LANG=enus) tells us that the
// base address for PIN_CNF registers is 0x5000_0000 (page 231). The offset for GPIO21 is 0x754 and for GPIO28 it is 0x770
// (page 232). We control the value of the pins using the OUT register. To set pin 21 high, we need to
// write 1 to bit 21 of the OUT register (page 232). The offset for the OUT register is 0x504 (page 231).

const GPIO0_PINCNF21_ROW1_ADDR: *mut u32 = 0x5000_0754 as *mut u32;
const GPIO0_PINCNF28_COL1_ADDR: *mut u32 = 0x5000_0770 as *mut u32;
const ROW_PINS: [(u8, u32); 5] = [(0, 21), (0, 22), (0, 15), (0, 24), (0, 19)];
const COL_PINS: [(u8, u32); 5] = [(0, 28), (0, 11), (0, 31), (1, 5), (0, 30)];

const GPIO0_BASE_ADDR: u32 = 0x5000_0000;
const GPIO1_BASE_ADDR: u32 = 0x5000_0300;

const CONFIG_REG_OFFSET: u32 = 0x700;
const REGISTER_LENGTH: u32 = 0x4;
const OUT_SET_REG_OFFSET: u32 = 0x508;
const OUT_CLR_REG_OFFSET: u32 = 0x50C;

const fn pin_config_address(port: u8, pin: u32) -> *mut u32 {
return (if port == 0 { GPIO0_BASE_ADDR } else { GPIO1_BASE_ADDR } + CONFIG_REG_OFFSET + (pin * REGISTER_LENGTH)) as *mut u32;
}

const fn out_set_address(port: u8) -> *mut u32 {
return (if port == 0 { GPIO0_BASE_ADDR } else { GPIO1_BASE_ADDR } + OUT_SET_REG_OFFSET) as *mut u32;
}

const fn out_clr_address(port: u8) -> *mut u32 {
return (if port == 0 { GPIO0_BASE_ADDR } else { GPIO1_BASE_ADDR } + OUT_CLR_REG_OFFSET) as *mut u32;
}

const DIR_OUTPUT_POS: u32 = 0; // Bit in configuration register to choose between input and output (page 269)
const PINCNF_DRIVE_LED: u32 = 1 << DIR_OUTPUT_POS; // 1 means output, 0 means input (page 269) -> we need 1

// Configure the direction of the pins to output
// Configure the direction of the row and col pins to output
unsafe {
for (port, pin) in ROW_PINS {
let addr = pin_config_address(port, pin);
write_volatile(addr, PINCNF_DRIVE_LED);
}

for (port, pin) in COL_PINS {
let addr = pin_config_address(port, pin);
write_volatile(addr, PINCNF_DRIVE_LED);
}
}

unsafe {
// Set the direction of the pins 21 and 28 to output
write_volatile(GPIO0_PINCNF21_ROW1_ADDR, PINCNF_DRIVE_LED);
write_volatile(GPIO0_PINCNF28_COL1_ADDR, PINCNF_DRIVE_LED);
// Initialize: rows LOW (off) and columns HIGH (off)
for (port, pin) in ROW_PINS {
write_volatile(out_clr_address(port), 1 << pin); // Keep rows LOW initially
}

for (port, pin) in COL_PINS {
write_volatile(out_set_address(port), 1 << pin); // Keep columns HIGH initially
}
}

const GPIO0_OUT_ADDR: *mut u32 = 0x5000_0504 as *mut u32;
const GPIO0_OUT_ROW1_POS: u32 = 21; // Bit in the OUT register to control GPIO21
const DISPLAY: [[bool; 5]; 5] = [
[true, false, false, false, true],
[false, true, false, true, false],
[false, false, true, false, false],
[false, true, false, true, false],
[true, false, false, false, true],
];

let mut is_on = false;
loop {
rprintln!("Echo...");
unsafe {
// Set the value of the OUT register to turn on or off the LED
// We do not set the value for GPIO28 because we want it to be off
write_volatile(GPIO0_OUT_ADDR, (is_on as u32) << GPIO0_OUT_ROW1_POS);
}
if is_on {
for _ in 0..500 {
for (row_idx, row) in DISPLAY.into_iter().enumerate() {
// Set current row to HIGH (active)
write_volatile(out_set_address(ROW_PINS[row_idx].0), 1 << ROW_PINS[row_idx].1);

for (col_idx, visible) in row.into_iter().enumerate() {
if visible {
// For visible pixels, set column to LOW
write_volatile(out_clr_address(COL_PINS[col_idx].0), 1 << COL_PINS[col_idx].1);
} else {
// For invisible pixels, keep column HIGH
write_volatile(out_set_address(COL_PINS[col_idx].0), 1 << COL_PINS[col_idx].1);
}
}

for _ in 0..100 {
nop();
}

// Reset columns to HIGH before moving to next row
for (port, pin) in COL_PINS {
write_volatile(out_set_address(port), 1 << pin);
}

// Set current row back to LOW
write_volatile(out_clr_address(ROW_PINS[row_idx].0), 1 << ROW_PINS[row_idx].1);
}
}

for _ in 0..100_000 {
nop();
} else {
// Turn off all LEDs by setting all rows LOW and all columns HIGH
for (port, pin) in ROW_PINS {
write_volatile(out_clr_address(port), 1 << pin);
}
for (port, pin) in COL_PINS {
write_volatile(out_set_address(port), 1 << pin);
}

// Add delay for the off state
for _ in 0..300000 {
nop();
}
}
}

is_on = !is_on;
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