mmix-mem.w

% This file is part of the MMIXware package (c) Donald E Knuth 1999
@i boilerplate.w %<< legal stuff: PLEASE READ IT BEFORE MAKING ANY CHANGES!

\def\title{MMIX-MEM}
\def\MMIX{\.{MMIX}}
\def\Hex#1{\hbox{$^{\scriptscriptstyle\#}$\tt#1}} % experimental hex constant
@s octa int

@* Memory-mapped input and output. This module supplies procedures for reading
@^I/O@>
@^input/output@>
@^memory-mapped input/output@>
from and writing to \MMIX\ memory addresses that exceed 48 bits. Such addresses
are used by the operating system for input and output, so they require special
treatment. At present only dummy versions of these routines are implemented.
Users who need nontrivial versions of |spec_read| and/or |spec_write| should
prepare their own and link them with the rest of the simulator.

Many I/O devices communicate via bytes or wydes or tetras instead of
octabytes. So these prototype routines have a |size| parameter, to
distinguish between the various kinds of quantities that \MMIX\ wants to
read from and write to the memory-mapped addresses.

@p
#include <stdio.h>
#include "mmix-pipe.h" /* header file for all modules */
extern octa read_hex(); /* found in the main program module */
static char buf[20];
static char *kind[]={"byte","wyde","tetra","octa"};
extern octa shift_left @,@,@[ARGS((octa y,int s))@];
  /* $y\LL s$, $0\le s\le64$ */
extern octa shift_right @,@,@[ARGS((octa y,int s,int u))@];
  /* $y\GG s$, signed if |!u| */

@ If the |interactive_read_bit| of the |verbose| control is set,
the user is supposed to supply values dynamically. Otherwise
zero is read.

@p
octa spec_read @,@,@[ARGS((octa,int))@];@+@t}\6{@>
octa spec_read(addr,size)
  octa addr;
  int size;
{
  octa val;
  size&=0x3, addr.l&=-(1<<size);
  if (verbose&interactive_read_bit) {
    printf("** Read %s from loc %08x%08x: ",kind[size],addr.h,addr.l);
    fgets(buf,20,stdin);
    val=read_hex(buf);
  } else val.l=val.h=0;
  switch (size) {
case 0: val.l&=0xff;
case 1: val.l&=0xffff;
case 2: val.h=0;
case 3: break;
}
  if (verbose&show_spec_bit) {
    printf("   (spec_read ");
    switch (size) {
  case 0: printf("%02x",val.l);@+break;
  case 1: printf("%04x",val.l);@+break;
  case 2: printf("%08x",val.l);@+break;
  case 3: printf("%08x%08x",val.h,val.l);@+break;
    }
    printf(" from %08x%08x at time %d)\n",addr.h,addr.l,ticks.l);
  }
  return shift_left(val,(8-(1<<size)-(addr.l&7))<<3);
}

@ The default |spec_write| just reports its arguments, without actually
writing anything.

@p
void spec_write @,@,@[ARGS((octa,octa,int))@];@+@t}\6{@>
void spec_write(addr,val,size)
  octa addr,val;
  int size;
{
  if (verbose&show_spec_bit) {
    size&=0x3, addr.l&=-(1<<size);
    val=shift_right(val,(8-(1<<size)-(addr.l&7))<<3,1);
    printf("   (spec_write ");
    switch (size) {
  case 0: printf("%02x",val.l);@+break;
  case 1: printf("%04x",val.l);@+break;
  case 2: printf("%08x",val.l);@+break;
  case 3: printf("%08x%08x",val.h,val.l);@+break;
    }
    printf(" to %08x%08x at time %d)\n",addr.h,addr.l,ticks.l);
  }
}

@ Incidentally, the combined address $a$ and size $s$ could be transmitted
in 64 bits of an actual memory bus, because $a$ is always a multiple of~$2^s$
that is less than $2^{63}$. Thus $(a,s)$ can be packed neatly into the
64-bit number $2a+2^s$. (Think about it.)

@* Index.