fix(09): Correct PL011 UART newline and add Pi 5 baud rate

Makes two improvements to the shared bcm2xxx_pl011_uart driver:

1. Conditionally sets the baud rate to 115200 when compiling for 'bsp_rpi5'.

2. Fixes terminal display by implementing '\n' to '\r\n' translation in the 'write_char' function, ensuring correct cursor positioning for all output.

Author: devansh-lodha

09_privilege_level/src/bsp/device_driver/bcm/bcm2xxx_pl011_uart.rs

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 //
-// Copyright (c) 2018-2023 Andre Richter <andre.o.richter@gmail.com>
+// Copyright (c) 2018-2025 Andre Richter <andre.o.richter@gmail.com>
 
 //! PL011 UART driver.
 //!
@@ -201,22 +201,6 @@ impl PL011UartInner {
     }
 
     /// Set up baud rate and characteristics.
-    ///
-    /// This results in 8N1 and 921_600 baud.
-    ///
-    /// The calculation for the BRD is (we set the clock to 48 MHz in config.txt):
-    /// `(48_000_000 / 16) / 921_600 = 3.2552083`.
-    ///
-    /// This means the integer part is `3` and goes into the `IBRD`.
-    /// The fractional part is `0.2552083`.
-    ///
-    /// `FBRD` calculation according to the PL011 Technical Reference Manual:
-    /// `INTEGER((0.2552083 * 64) + 0.5) = 16`.
-    ///
-    /// Therefore, the generated baud rate divider is: `3 + 16/64 = 3.25`. Which results in a
-    /// genrated baud rate of `48_000_000 / (16 * 3.25) = 923_077`.
-    ///
-    /// Error = `((923_077 - 921_600) / 921_600) * 100 = 0.16%`.
     pub fn init(&mut self) {
         // Execution can arrive here while there are still characters queued in the TX FIFO and
         // actively being sent out by the UART hardware. If the UART is turned off in this case,
@@ -240,9 +224,26 @@ impl PL011UartInner {
         // updated on a single write strobe generated by a LCR_H write. So, to internally update the
         // contents of IBRD or FBRD, a LCR_H write must always be performed at the end.
         //
-        // Set the baud rate, 8N1 and FIFO enabled.
-        self.registers.IBRD.write(IBRD::BAUD_DIVINT.val(3));
-        self.registers.FBRD.write(FBRD::BAUD_DIVFRAC.val(16));
+        // Set the baud rate.
+        #[cfg(feature = "bsp_rpi5")]
+        {
+            // For Pi 5, use the known-good 115200 baud configuration.
+            // This is proven to work with the default 48MHz UART clock.
+            // BAUDDIV = 48,000,000 / (16 * 115200) = 26.0416...
+            // IBRD = 26, FBRD = 3
+            self.registers.IBRD.write(IBRD::BAUD_DIVINT.val(26));
+            self.registers.FBRD.write(FBRD::BAUD_DIVFRAC.val(3));
+        }
+        #[cfg(not(feature = "bsp_rpi5"))]
+        {
+            // Original configuration for RPi3/4 at 921600 baud.
+            // BAUDDIV = 48_000,000 / (16 * 921_600) = 3.2552...
+            // IBRD = 3, FBRD = 16
+            self.registers.IBRD.write(IBRD::BAUD_DIVINT.val(3));
+            self.registers.FBRD.write(FBRD::BAUD_DIVFRAC.val(16));
+        }
+
+        // Set 8N1 and FIFO enabled.
         self.registers
             .LCR_H
             .write(LCR_H::WLEN::EightBit + LCR_H::FEN::FifosEnabled);
@@ -255,7 +256,18 @@ impl PL011UartInner {
 
     /// Send a character.
     fn write_char(&mut self, c: char) {
-        // Spin while TX FIFO full is set, waiting for an empty slot.
+        // If the character is a newline, prepend a carriage return.
+        if c == '\n' {
+            // Spin while TX FIFO full is set.
+            while self.registers.FR.matches_all(FR::TXFF::SET) {
+                cpu::nop();
+            }
+            // Write the carriage return character.
+            self.registers.DR.set('\r' as u32);
+        }
+
+        // Now, send the original character.
+        // Spin while TX FIFO full is set.
         while self.registers.FR.matches_all(FR::TXFF::SET) {
             cpu::nop();
         }
@@ -292,7 +304,8 @@ impl PL011UartInner {
         // Read one character.
         let mut ret = self.registers.DR.get() as u8 as char;
 
-        // Convert carrige return to newline.
+        // Convert carriage return to newline. This is a standard behavior
+        // for console input.
         if ret == '\r' {
             ret = '\n'
         }
@@ -316,6 +329,7 @@ impl PL011UartInner {
 impl fmt::Write for PL011UartInner {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         for c in s.chars() {
+            // The `write_char` function now correctly handles `\n` -> `\r\n` conversion.
             self.write_char(c);
         }