Add UART capture script, Makefile, updated README with prerequisites

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

capture_uart.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# RK3588 DDR Training UART Capture
+# Connect USB-UART to Rock 5 ITX+ debug header (1.5Mbaud, 3.3V)
+# Run this BEFORE booting/rebooting the board
+
+UART=${1:-/dev/ttyUSB0}
+BAUD=1500000
+LOGDIR=~/src/rk3588-ddr-decompiled/uart_logs
+TIMESTAMP=$(date +%Y%m%d_%H%M%S)
+LOGFILE="$LOGDIR/ddr_training_${TIMESTAMP}.log"
+
+mkdir -p "$LOGDIR"
+
+echo "Capturing DDR training output from $UART at ${BAUD}baud"
+echo "Log: $LOGFILE"
+echo "Press Ctrl+C to stop after boot completes"
+echo ""
+
+stty -F "$UART" "$BAUD" cs8 -cstopb -parenb raw -echo
+cat "$UART" | tee "$LOGFILE"