diff options
Diffstat (limited to 'Lesson_17/README.md')
| -rw-r--r-- | Lesson_17/README.md | 91 |
1 files changed, 0 insertions, 91 deletions
diff --git a/Lesson_17/README.md b/Lesson_17/README.md deleted file mode 100644 index 6dd3ed6..0000000 --- a/Lesson_17/README.md +++ /dev/null @@ -1,91 +0,0 @@ -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: - - -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. - |