spacemoai

@spacemoai.tni.nl

95 Followers 15 Following

I travel the galaxy and far beyond. Got to live the life I create inside my head. Not happy to hide my big dreams anymore. Leaving all but the future far behind. Please support my #MSX work at https://buymeacoffee.com/tni.nl

An SX-E prototype, cartridges for V9968 and Y8960, just missing the FPGA modules.

Thoughts on Cache

Generally speaking there are two caching strategies for working memory: a (shared) cache for memory reads and writes, or a separate cache for CPU instruction fetches and memory read/writes.
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Shared cache

A problem of shared cache is pollution from data read/writes, which are generally more random than instruction fetches (ie. temporal and spatial reference locality is lower). This causes more frequent cache collisions. A possible solution to this is to increase the size of the cache.

Separate caches

Separate caches for instructions (I-cache) and data (D-cache) avoid cache pollution by taking advantage of the local and sequential nature of CPU instruction fetches. However, this introduces the problem of losing cache coherence when data is written. For example, when loading a new program or overlay in memory, the program data is written by D-cache stores and the I-cache needs to be invalidated. The same applies to self-modifying code or JIT compiled code.

Invalidation of the I-cache can be solved in two ways:
- Automatic: every data write checks the I-cache to see if there is a hit, and if so, invalidates the cache line.
- Manual: after modifying memory that may contain CPU instructions, the affected I-cache lines must be invalidated by an explicit mechanism, such as a CPU instruction, either by the OS or the user program.

Announcement of a

A penguin princess thinking of a moai statue.

Me sharing Francis Charing's Chair, and Mr. Nishi discussing the future of MSX.

Photo of the Mitsubishi ML-800 MSX computer

A virtual certificate with text "Celebrating 10M users on Bluesky, #4,998,283, spacemoai ‪@spacemoai.bsky.social‬, joined on Feb 27, 2024"

A rescue setup with an open desktop tower, connected to a stack of external disks in server caddies. A monitor, keyboard, mouse and a compact 1U server are also visible.

A screenshot of a post describing and showing a display glitch of the number of lives in Namcot's Dig Dug on MSX2, versus the correct display on MSX1.