calculate the reload value at compilation time in the Makefile

Author: bemxio

Makefile

@@ -15,6 +15,9 @@ EXECUTABLE = bootloader.bin
 
 VIDEO_PATH = video.flv
 
+FPS = $(shell ffmpeg -i $(VIDEO_PATH) 2>&1 | sed -n "s/.*, \(.*\) fp.*/\1/p")
+RELOAD_VALUE = $(shell expr 1193182 / $(FPS))
+
 ASCII_GRADIENT = oxxo
 
 # targets
@@ -33,10 +36,9 @@ $(BUILD_DIR)/$(EXECUTABLE): $(BUILD_DIR)/code.bin $(BUILD_DIR)/data.bin
 $(BUILD_DIR)/code.bin: $(SOURCES)
 	mkdir -p $(BUILD_DIR)
 
-	$(AS) $(ASFLAGS) $< -o $@
+	$(AS) $(ASFLAGS) -DPIT_RELOAD_VALUE=$(RELOAD_VALUE) $< -o $@
 
 $(BUILD_DIR)/data.bin: $(VIDEO_PATH)
 	mkdir -p $(BUILD_DIR)
 
-	$(PYTHON) $(SRC_DIR)/converter/main.py $< -o $@ \
-		--gradient $(ASCII_GRADIENT)
+	$(PYTHON) $(SRC_DIR)/converter/main.py --gradient $(ASCII_GRADIENT) $< -o $@

README.md

@@ -10,19 +10,19 @@ To build the bootloader in the easiest way, just follow the instructions below.
 You can do it the manual way with an assembler, a video to ASCII converter and a virtualization software of your choice too, but then, you're on your own.
 
 ### Installing dependencies
-For Windows, you can install [`scoop`](https://scoop.sh/) and run:
+For Windows, you can install [Scoop](https://scoop.sh/) and run:
 ```powershell
-scoop install nasm make python
+scoop install nasm make ffmpeg python
 ```
 
 As for Linux, all of the packages should be in your default package manager. Here's an example for Ubuntu:
 ```bash
-sudo apt install nasm make python3
+sudo apt install nasm make ffmpeg python3
 ```
 
 If you want to run the bootloader, you need to install QEMU as well, which can be done with either `scoop install qemu` or `sudo apt install qemu`, depending on your operating system.
 
-Once you have Python installed, you will also need to install the dependencies for the `vid2data` converter. Simply do:
+Once you have Python installed, you will also need to install the dependencies for the ASCII converter. Simply do:
 ```bash
 python3 -m pip install -r src/vid2data/requirements.txt
 ```
@@ -46,13 +46,8 @@ By default, the Makefile uses KVM as an accelerator for QEMU. Since KVM is exclu
 #### It's too slow/fast and/or the frame rate is unstable!
 ~~In the future, I might implement something bigger, like a custom interrupt handler, to get a stable frame rate.~~
 
-After like a month or maybe even more, I finally understood how to set up the PIT and add a handler in the IVT, thus, the framerate is now fully faithful to the original! If it's still going too slow/fast though, you might need to adjust the `PIT_RELOAD_VALUE` value on line 2 in [`src/pit.asm`](src/pit.asm).
-
-To calculate the reload value, simply use the equation:
-```
-Reload Value = floor(1193182 / FPS)
-```
-where `FPS` is the framerate of the original video.
+After like a month or maybe even more, I finally understood how to set up the PIT and add a handler in the IVT, thus, the framerate is now fully faithful to the original!
+If it is still too slow, that means your CPU might not be able to handle the video at the original framerate. In that case, you can change the `FPS` variable in the `Makefile` to a lower value.
 
 ## FAQ
 
@@ -61,7 +56,8 @@ There are two main reasons for this project:
 
 Firstly, I wanted to learn more about low-level programming, more specifically Assembly. I already made [an operating system](https://github.com/bemxio/bemxos), however, the Assembly side has attracted me the most. I wanted to challenge myself into using it for something bigger, in order to properly learn registers, interrupts and things like that. Perhaps, in the future, I will step into NES development!
 
-~~Secondly, no one has done this before.~~ Actually, I was wrong. [@redstone_flash5774](https://www.youtube.com/channel/UCxL3ay5lRA4KvCX56sRIUeA) made their version and uploaded it to YouTube [here](https://www.youtube.com/watch?v=DsJH3SNYqvM). I didn't notice it at all in those 6 months, just found it out when I was uploading my video on YouTube. Still, our approaches to do it are different, and they have not uploaded the source code, so I guess I can still be proud of it!
+~~Secondly, no one has done this before.~~
+Actually, I was wrong. [@redstone_flash5774](https://www.youtube.com/channel/UCxL3ay5lRA4KvCX56sRIUeA) made their version and uploaded it to YouTube [here](https://www.youtube.com/watch?v=DsJH3SNYqvM). I didn't notice it at all in those 6 months, just found it out when I was uploading my video on YouTube. Still, our approaches to do it are different, and they have not uploaded the source code, so I guess I can still be proud of it!
 
 ### How does it work?
 The `bootloader.bin` file is split into two parts - the first one is the bootloader itself, with all of the code, and the second one is the video data. 

src/pit.asm

@@ -1,13 +1,13 @@
 IVT_IRQ0_OFFSET equ 0x0020 ; the offset of the first IRQ in the IVT
-PIT_RELOAD_VALUE equ 0x9b5c ; the reload value for the PIT (0x9b5c, 39722, results in 30 hz/FPS)
+;PIT_RELOAD_VALUE equ 0x9b5c ; the reload value for the PIT (0x9b5c, 39772, results in 30 hz/FPS)
 
 setup_pit:
     pusha ; save the registers
 
     mov al, 0x34 ; set the command byte (channel 0, lobyte/hibyte, rate generator)
     out 0x43, al ; send the command byte to the PIT
 
-    mov ax, PIT_RELOAD_VALUE ; set the reload value (0x9b5c, 39722, results in 30 hz/FPS)
+    mov ax, PIT_RELOAD_VALUE ; set the reload value
 
     out 0x40, al ; send the low byte to the PIT