Move lessons to separate folder

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>

1 files changed, 91 insertions, 0 deletions

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+In the last lesson we've added our own boot option.
+
+Let's boot it.
+
+Type `exit` in the UEFI shell to go to the BIOS menu:
+```
+Shell> exit
+```
+Navigate to the `Boot Manager` window. Our `HelloWorld` option would be present here:
+![Boot Manager](BootManager.png?raw=true "Boot manager")
+
+If you'll try to boot it, app would print its strings and immediately return.
+
+Let's fix it. Let's add wait for a key input from user in our app code.
+To do it we will need `WaitForEvent` blocking function:
+
+```
+EFI_BOOT_SERVICES.WaitForEvent()
+
+Summary
+Stops execution until an event is signaled.
+
+Prototype
+typedef
+
+EFI_STATUS
+(EFIAPI *EFI_WAIT_FOR_EVENT) (
+ IN UINTN NumberOfEvents,
+ IN EFI_EVENT *Event,
+ OUT UINTN *Index
+);
+
+Parameters
+NumberOfEvents 	The number of events in the Event array.
+Event 		An array of EFI_EVENT.
+Index 		Pointer to the index of the event which satisfied the wait condition.
+```
+
+To our task we should use `EFI_EVENT WaitForKey` from the `EFI_SIMPLE_TEXT_INPUT_PROTOCOL` (which is placed in a `gST->ConIn`)
+```
+typedef struct _EFI_SIMPLE_TEXT_INPUT_PROTOCOL {
+ EFI_INPUT_RESET Reset;
+ EFI_INPUT_READ_KEY ReadKeyStroke;
+ EFI_EVENT WaitForKey;
+} EFI_SIMPLE_TEXT_INPUT_PROTOCOL;
+```
+
+Now when we now all this API add this code to the end of the `HelloWorld` app main function:
+```
+UINTN Index;
+gBS->WaitForEvent(1, &(gST->ConIn->WaitForKey), &Index);
+```
+
+Compile OVMF again and try to boot our `HelloWorld` boot option through the `Boot Manager` BIOS menu.
+Now output of the app stops and waits for the user keystroke.
+
+Everything works fine except a fact that if we choose `Enter` as our keystroke, `HelloWorld` app would be immediately launched again.
+
+This happens because we didn't read or clear the input buffer. As we don't need keystroke information let's simply reset it with a `Reset` function:
+```
+EFI_SIMPLE_TEXT_INPUT_PROTOCOL.Reset()
+
+Summary:
+Resets the input device hardware.
+
+Prototype:
+typedef
+EFI_STATUS
+(EFIAPI *EFI_INPUT_RESET) (
+ IN EFI_SIMPLE_TEXT_INPUT_PROTOCOL *This,
+ IN BOOLEAN ExtendedVerification
+ );
+
+Parameters:
+This 			A pointer to the EFI_SIMPLE_TEXT_INPUT_PROTOCOL instance.
+ExtendedVerification	Indicates that the driver may perform a more exhaustive verification
+			operation of the device during reset.
+
+Description:
+The Reset() function resets the input device hardware.
+The implementation of Reset is required to clear the contents of any input queues resident in memory
+used for buffering keystroke data and put the input stream in a known empty state
+```
+
+Add this to the end of our app:
+```
+gST->ConIn->Reset(gST->ConIn, FALSE);
+```
+
+Now if we boot our app from the `Boot Manager` BIOS menu it would work correctly for any keystroke.
+