Auth: Mitran Andrei Group: 1231EA
Project is divided into two parts: • emu8086 part: computes frame buffer size + I2C timing and PRINTS it. It also SIMULATES communication with Arduino by building a serial line in RAM and printing it. • Arduino part: hosts a local web page that works as a control panel. It captures a frame and returns it as JPEG. At boot it also calls Xtensa assembly to compute the same frame/I2C math and prints it to Serial.
• Browser -> ESP32 HTTP server: GET / (UI), GET /capture (image). • ESP32 camera driver: esp_camera_fb_get() grabs a frame buffer. • If sensor supports JPEG: send JPEG directly; otherwise capture RGB565 and convert to JPEG with fmt2jpg(). • Computation: Xtensa assembly function emu8086_xtensa() computes the same values as the emu8086 program.
A) Frame buffer size (bytes) frame_bytes = WIDTH * HEIGHT * BPP WIDTH, HEIGHT are pixels BPP is bytes per pixel (RGB565 = 2, grayscale = 1, etc.) In 8086 we store the result as 32bit (FRAME_HI:FRAME_LO). In ESP32 we use a 64-bit intermediate and keep lo/hi words. B) I2C timing total_cycles = APB_KHZ / SCL_KHZ high_cycles = total_cycles / 2 low_cycles = total_cycles - high_cycles remainder = APB_KHZ % SCL_KHZ (only for debug / accuracy checks) Interpretation: this is a simplified way to estimate how many APB clock cycles fit in one I2C clock period.
Emu program runs in a PC/DOS emulator, so it cannot really talk to an ESP32 over COM1 (for me it was COM14) in a reliable way. o Instead of writing the whole program in assembly (Instead of the intended driver only, of course), I choose to simulate the steps in 8086 and translate this driver in xtensa assembly for arduino process. • Build the line: FB=,T=,H=,L= into COMBUF. • Print: “Sending to COM1 as: ” • This avoids BIOS INT 14h issues like “interrupt not defined yet”.
Arduino sketch is responsible for:
• Connecting to WiFi and prints local IP.
• Serves web page in order to control the camera
• Button loads /capture (cache-busted) into an tag.
• Server handler captures a frame and returns image/jpeg.
The Arduino code calls an external Xtensa assembly function: extern "C" void emu8086_xtensa(uint32_t w, uint32_t h, uint32_t bpp, uint32_t apb_khz, uint32_t scl_khz, ComputeOut* out); This function computes: • frame_bytes (low 32 bits stored in out->frame_bytes_lo) • total_cycles, high_cycles, low_cycles
Note: I used “mull” for the low 32-bit product, and __udivsi3 for division (portable even if hardware divide is not enabled).
• “JPEG format is not supported on this sensor”: start camera in RGB565 and convert to JPEG in /capture. • Xtensa: “unknown opcode mul”: use mull/muluh (or only mull if you only keep low 32). • Xtensa: “unaligned entry instruction”: keep .align 4 before the function label. • If /capture is slow: use smaller frame size (QVGA) or lower JPEG quality number for better quality / higher CPU cost trade-off. Issues only: Overflow (program cant go for something like 800Mhz. As well as arduino doesn’t support my assembly code without xtensa.
Computation Results
Output nr = 1
Frame bytes = 153600
I2C: total_cycles = 200
I2C: high_cycles = 100
I2C: low_cycles = 100
Sending to COM1 as: FB=153600,T=200,H=100,L=100
Press R to recompute, ESC to quit...
Sources: https://medium.com/@bayotosho/xtensa-lx7-assembly-walkthrough-by-example-c43f529bdeb1 https://www.instructables.com/How-to-Use-the-ESP32-CAM-for-Beginners/ https://randomnerdtutorials.com/esp32-cam-video-streaming-face-recognition-arduino-ide/ https://docs.platformio.org/en/latest/boards/espressif32/esp32cam.html https://documentation.espressif.com/esp32_technical_reference_manual_en.pdf https://medium.com/@aleksej.gudkov/8086-assembly-code-examples-a-beginners-guide-3aeafd3fa808 https://yassinebridi.github.io/asm-docs/asm_tutorial_01.html