Interrupts

[mkopec]

• Make more functions __reentrant to free up internal ram
• Increase SRAM_SIZE to 3.5K to get more XSEG for free
• Implement keyboard scan matrix mode instead of scanning the matrix in firmware
• Implement interrupt handling in the main loop
• Add 1ms sleep to the main loop
• Split power.c from one large monolithic power_event into per-signal handlers and dispatch them from IRQ
• Added debug command interface for remote power control over DBGR/SMB

Reduces power usage and improves performance and responsiveness. No functional changes.

  ┌──────────────────────────┬─────────────────┬───────────────────┬──────────────┐
  │          Metric          │ master baseline │ interrupts branch │    Delta     │
  ├──────────────────────────┼─────────────────┼───────────────────┼──────────────┤
  │ Stack (DSEG free)        │ 132 bytes       │ 204 bytes         │ +72 bytes    │
  ├──────────────────────────┼─────────────────┼───────────────────┼──────────────┤
  │ XSEG (External RAM used) │ 1533 bytes      │ 1511 bytes        │ −22 bytes    │
  ├──────────────────────────┼─────────────────┼───────────────────┼──────────────┤
  │ ROM                      │ 38,372 bytes    │ 40,568 bytes      │ +2,196 bytes │
  └──────────────────────────┴─────────────────┴───────────────────┴──────────────┘

Needs full regression testing.

Tested on NV40MB:

• PMC works
• SMFI works
• KBC works
• kbscan works
• battery charging works
• power on / off works
• suspend works

No regressions spotted so far.