About Proposals

• A few overlapping topics: find unique/interesting perspectives
  • Audio/PWM
  • Video/HDMI
  • Writable FS

Audio/PWM

• How to mix two or more audios, like your laptop?
• How to design system calls for user program (e.g., fd/dev)?
• How to design device driver interfaces (e.g., ioctl)?
• How to orchestrate them in the interrupt handler?

Video/HDMI

• How to design GUI interface like X.org?
• How to utilize Video Core?
• Can you support 3d rendering?

Writable SDCard

• What would be the right interface/syscalls?
• How to handle a file descriptor (we don’t have!)?
• What if the power goes off in the middle of writing a big file?
• When are you going to update FAT (sync/datasync)?
• (e.g., Encrypted FS is a good way to differentiate!)

Quiz

• [30 point] Rust → Lectures on Rust 1-6
• [30 point] Heap allocator → LEC 13
• [40 point] File system → LEC 11

→ Complete/review your Lab3 before the exam!

Review: Heap allocator

• Understand pros/cons of these two allocators:
  • Bump allocator: simplest form, no reuse/free
  • Bin allocator: attempting to minimize fragmentation
• Think of how to address cons?

Ref. Allocator Designs

Bump allocator

• Q. How to do alloc()?
• Q. How to do free()?
• Q. How to handle layout (i.e., alignment)?

Maintaining free chunks for reuse

• Q. How to do free()?
• Q. How to do alloc()?
• Q. Where to store “link” then?

Bin allocator

• Introducing size-based caching on freed chunks
• Maintaining a linked list per a group of free chunks with similar sizes (i.e., bin)
• Q. How to do alloc()?
• Q. How to do free()?

      Bins
sz=16 [ -]--->[fd]--->[fd]-->NULL
sz=24 [ -]--->[fd]--->NULL
sz=32 [ -]--->NULL
       ...

Review: FAT32

• Be familiar with the FAT disk layout
• What’s the role of FAT?
• How to structure FAT?
• How the size of a file would be determined?

Fat32 Overview: Disk Layout

• Starts with (extended) BIOS Parameter Block (E/BPB)
• Followed by FAT (File Allocation Table)
• Followed by Cluster

About FAT

• Entry 0: indicating ID (ok to ignore)
• Entry 1: indicating a special maker for the end of cluster (EOC)
• Other special markers: e.g., 0x?FFFFFF7 for bad sectors

Example FAT