Document PgUp, pci.sh request fact irq

README.md

@@ -57,6 +57,15 @@ We use `printk` a lot, and it shows on the QEMU terminal by default. If that ann
 
 See also: <https://superuser.com/questions/351387/how-to-stop-kernel-messages-from-flooding-my-console>
 
+You can scroll up a bit on the default TTY with:
+
+    Shift + PgUp
+
+How to increase the buffer:
+
+- <https://askubuntu.com/questions/709697/how-to-increase-scrollback-lines-in-ubuntu14-04-2-server-edition>
+- <https://unix.stackexchange.com/questions/346018/how-to-increase-the-scrollback-buffer-size-for-tty>
+
 We use Buildroot's default kernel version, you can confirm it after build with:
 
     grep BR2_LINUX_KERNEL_VERSION buildroot/.config

kernel_module/character_device.c

@@ -15,6 +15,8 @@ conlicts with other devices.
 
 Then we need to check /proc/devices to find out the assigned number,
 and use that for the mknod.
+
+- https://unix.stackexchange.com/questions/37829/understanding-character-device-or-character-special-files/371758#371758
 */
 
 #include <asm/uaccess.h> /* copy_from_user, copy_to_user */

rootfs_overlay/pci.sh

@@ -17,8 +17,11 @@ dd bs=4 status=none if=/dev/lkmc_pci count=1 skip=1 | od -An -t x1
 # => 0F0F0F0F
 
 # Factorial calculator.
+# Request interrupt when the computation is over.
+printf '\x80\x00\x00\x00' | dd bs=4 status=none of=/dev/lkmc_pci count=1 seek=8
 # factorial(0xC) = 0x1c8cfc00
 printf '\x0C\x00\x00\x00' | dd bs=4 status=none of=/dev/lkmc_pci count=1 seek=2
+# => interrupt
 sleep 1
 dd bs=4 status=none if=/dev/lkmc_pci count=1 skip=2 | od -An -t x1
 dd bs=4 status=none if=/dev/lkmc_pci count=1 skip=8 | od -An -t x1