feat: Raspberry Pi 4/400 Bluetooth over mini UART (H4, Broadcom patchram, firmware mailbox BT_ON); move BT stack to Drivers/Bluetooth

scripts/mk-rpi4-sd.sh

@@ -165,10 +165,18 @@ IMG="$WORK/esp.fat"
 dd if=/dev/zero of="$IMG" bs=1M count=0 seek=$esp_mib status=none
 mformat -i "$IMG" -F -v MONTAUK ::
 
-# Firmware: everything in the release except its readme.
+# Firmware: everything in the release except its readme. Its config.txt
+# gets the VPU core clock pinned: the miniuart-bt overlay leaves Bluetooth on
+# the mini UART, whose baud rate is derived from that clock, and the
+# overlay's documentation requires core_freq and core_freq_min to match or
+# the mini UART breaks when the firmware scales the clock (500 MHz is the
+# Pi 4/400 default).
 for f in "$FW_DIR"/*; do
     case "$(basename "$f")" in
         Readme.md) ;;
+        config.txt)
+            { cat "$f"; printf '\ncore_freq=500\ncore_freq_min=500\n'; } > "$WORK/config.txt"
+            mcopy -i "$IMG" "$WORK/config.txt" :: ;;
         *) mcopy -s -i "$IMG" "$f" :: ;;
     esac
 done