Bugs to fix:
* render:    figure out why fx-CG dclear() now takes 4.1 ms instead of 2.6 ms

Extensions on existing code:
* clock:     mono support
* usb:       and interrupt pipes
* fs:        support RAM files
* fs:        support USB streams as generic file descriptors
* fugue:     support glob() to abstract away BFile entirely
* fugue/fs:  offer a primitive to remove recursively, which is native in Fugue
* bfile:     implement the optimization-restart as realized by Kbd2
* kernel:    better restore to userspace before panic (ensure BL=0 IMASK=0)
* project:   add license file
* kernel:    group linker script symbols in a single header file
* r61524:    brightness control and clean the file
* core:      review forgotten globals and MPU addresses not in <gint/mpu/*.h>
* core:      run destructors when a task-switch results in leaving the app
* fs:        support read-only files backed with GetBlockAddress() on fx-CG
* kernel:    SH4- or G-III-specific linker scripts?
* render:    Properly document bopti fx. Also make it faster maybe?

Future directions:
* Audio playback using TSWilliamson's libsnd method
* Serial communication
* Make fx9860g projects work out of the box on fxcg50
* Base for Yatis' threads library

Bits that need to abstract out into APIs:
- display: Toggle backlight (or set level)
  -> Have a backlight property with min/max values
  @ getkey
  @ justui jscene
- os: OS interface to access OS info, like in fxos
  @ usb/setup.c set_strings
  @ usb/classes/ff-bulk.c identify command
- render: current video mode
  @ usb/classes/ff-bulk.c capture_vram
- gray: make gray engine a subset of t6k11 which then supports two modes

Video formats:
- i1msb
- 2i1msb
- rgb565

T6K11:
  mode 0 :   i1msb   128x64   @64 Hz
  mode 1 :   2i1msb  128x64   @64 Hz
R61524:
  mode 0 :   rgb565  396x224  @? Hz
  mode 1 :   i3???   396x224  @? Hz
  mode 2 :   i1msb   128x64   @? Hz # <- for g1a emulation :)
  mode 3 :   2i1msb  128x64   @? Hz # <- for g1a emulation :)

enum {
    /* Indexed 1-bit, 0 is white, 1 is black. Row-major, left-to-right, each
       row a set of 4-byte values with leftmost pixel on the MSB. */
    IMAGE_FORMAT_I1MSB,
    /* Indexed 2-bit: white, light gray, dark gray, black. Represented as a
       pair of I1MSB buffers, the first being bit #0, the second bit #1. */
    IMAGE_FORMAT_2I1MSB,
};

fx-CP port progress.
DONE:
- kernel can start add-ins, take over interrupts (but no interrupt sources yet)
- panic handler works (no interactive choices, only RESET)
- no OS menu (likely never) and poweroff (maybe later)
- memory: 64 kB total + OS heap (no gint arena, no MMU)
- r61523: prototype display driver
- can use the rendering pipeline with no DMA acceleration
IN-PROGRESS:
- unification of the image/video interface
TODO:
- hardware info: rom and fs type
- quit handler
- DMA acceleration for dclear and dupdate
- keyboard and touch screen input
- drivers: cpg, dma, intc, rtc, tmu
- find more memory, 64 kB is not enough
- benchmark memory and display performance
- improve API and performance of display driver
- way off: filesystem, remote debugging, usb