nut32 explain

for week 4 lecture in Embedded Processor

This version completed nut31 with "let" "enum" and string.  Then implement an eval to prepare for a code generator.  Code generator is the last piece. It generates s-code for a stack processor.

step of work

1)  complete nut31
2)  write a small eval in nut run it with nsim
3)  write a s-code generator

23 June 2006
 
The nut32/nut.c is essentially the same as in nut31.  Only one bug fixed is char token[] which is previously declared as 20 char, now becomes 80 char (for storing the input token string).

The nut32/nsim.c is identical to nut31.

nut-in-nut compiler in nut32 (/test/nut.txt) is more complete, with "let" "enum" and string. The "evaluator" (or the n-code interpreter) is also implemented in nut, called "sim.txt" (also in /test).  It can execute n-code object.

sim.txt is an interim step to study a code generator.  To "eval" n-code, the n-code tree must be traversed.  The simplest way to do it is to do it recursively.  The "operational semantic" (how each code acts) is explicit in the nut-code for "eval" function.  The "eval" is only partially implemented.  It understands only 12 operators (just enough to support running the example "t2.txt"): if, do, add, call, lit, str, get, ld, st, ldx, fun, sys.

the test source file is as follows:

(enum 10 xAA xBB)
(let gv tv)

(def prints s ()
  (if (vec s 0)
    (do
    (sys 2 (vec s 0))
    (prints (+ s 1)))))

(def add1 x () (+ x 1))
(def main () ()
  (do
  (set tv 5)
  (prints "string")
  (sys 1 (add1 xBB))))

This test exercise "let", "enum" and string.  It outputs "string12" to the screen.

Detailed discussion of the simulator in nut is in a separate article.

This package is also include "gen.txt" the code generator.  The code generator reads n-code object and generates s-code (version som-v2) object.  The s-code object can be executed by somv2 (virtual machine).  s-code is the instruction set that will be supported by SX chip simulator (to be designed and implemented soon for future lecture).

27 June 2006