* pass interrupt test in amtest

riscv64-noop,input: add number key

See merge request projectn/nexus-am!13

Fence.i test

See merge request projectn/nexus-am!12

* The original code is not PIC, since it accesses a gloabl array. If we
  copy the code to somewhere else, it cannot access that global array
  any longer. To fix this, we pass the global array as function argument
  to make the code PIC.
* Now NOOP can pass the loader test with fence.i.

riscv64-noop,cte: use machine mode CSR

See merge request projectn/nexus-am!11

feat(rv64): update am to support riscv64-nanos

See merge request projectn/nexus-am!10

riscv64-nemu,cte: support timer interrupt from clint

See merge request projectn/nexus-am!9

feat(rv64): set up rv64 difftest environment

See merge request projectn/nexus-am!8

am,arch,platform,nemu: use $(MAKE) instead of make

See merge request projectn/nexus-am!7

*-nemu,trm: put mainargs at RAM to fix difftest bug

See merge request projectn/nexus-am!6

Rv64 cte

See merge request projectn/nexus-am!5

Riscv32 noop pal

See merge request projectn/nexus-am!4

* UART can only transmit character data, but not keystrobes.
* To do this, we record the last data UART received, By default we
  generate a keydown event. A keyup event is generated when
    * UART receive a different data from the last one
    * or no data is received in 0.5s
* This is not perfect. Key combination can not be detected since a keyup
  event is generated before another keydown event. But it is enough to
  play PAL with UART.

tests,cachetest: add loader test

See merge request projectn/nexus-am!3

Riscv32 noop

See merge request projectn/nexus-am!2

tests,cputest: add volatile to prevent optimization