Crucial, missing things.
! core:      the four basic memory functions
! core:      build an exception handler and a TLB miss handler
! core:      gint_switch() (driver contexts on stack; arbitrary code?)
! bopti:     fxcg50 version
! syscalls:  fxcg50 BFile calls
! gray:      the gray engine on fx9860g

Tests to run.
* core:      run the alignment/size automated tests for memory functions
* bopti:     more sizes, gray
* topti:     all charsets, colors

Complementary elements on existing code.
* dma:       dma_memcpy() and dma_memset(), possibly requiring alignment
* core:      use topti in the error message for missing mappings
* core:      find the #ifdef FX9860G|FXCG50 that have a cross-platform def
* topti:     support Unicode fonts
* hardware:  fill in the HWMEM_FITTLB flag
* keyboard:  think of extended functions
* cpg:       spread spectrum on fxcg50
* bopti:     blending modes for monochrome bitmaps (use topti assembler)
* display:   use more of topti's assembler in drect()
* core:      use cmp/str for memchr()
* timer:     try putting addresses in <gint/mpu/tmu.h>
* r61524:    brightness control and clean the file

Keep in mind.
* prizm:     don't hardcode stack address in fxcg50.ld
* prizm:     detect P1 static RAM (stack) in TLB
* core:      prove and use qdiv10() instead of __sdivsi3
* setjmp:    more registers may need to be saved
* core:      free heap when a task-switch results in leaving the app
* core:      save and restore interrupt masks
* timer:     make sure ETMU interrupts are disabled in ctx_restore()
* core:      document the SH7305 PFC in <gint/mpu/pfc.h>

Future directions.
* A complete file system abstraction
* Integrate overclock management
* Audio playback using Martin Poupe's method
* Serial communication [SCIF] [SCIFA]
* USB communication [USB]
* Driver for the watchdog timer [WDT] [SH7705]