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feat(v4): the machine has a ROM -- read and run, never written

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A read-only range of V4_ROM_WORDS words at V4_ROM_BASE, above RAM
(MACHINE.md 2, DATASHEET-F18.md 5).  Instruction fetch, @p and data fetches
read it; a running programme's store there is an address fault.  Attached by
the owner like every device; a reset detaches it.  The host node's range is
4096 words.  text.c places branches by the whole address space.  The
nucleus image is byte-identical.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
rajames
2026-10-15 11:25:24 -04:00
co-authored by Claude Opus 5.5
parent 42f8a13914
commit 32753f5479
7 changed files with 165 additions and 11 deletions
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v4/tests/test_host_rom_range.c
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/* test_host_rom_range.c -- the ROM is the machine's: read and run, never written.
*
* docs/v4.0.0/MACHINE.md section 2, DATASHEET-F18.md section 5. The ROM is a
* read-only range at V4_ROM_BASE, above RAM. An instruction fetch, an @p
* literal and a data fetch there read the ROM; a running programme's store
* there is an address fault. Like every device in the model it is attached
* by the node's owner, and a reset detaches it.
*/
#include "v4/asm.h"
#include "v4/testcode.h"
#include <stdio.h>
static int failures = 0, checks = 0;
#define CHECK(c,...) do{checks++; if(!(c)){failures++; printf("FAIL %s:%d: ",__FILE__,__LINE__); printf(__VA_ARGS__); printf("\n");}}while(0)
static v4_node n, scratch;
static v4_exec_state es;
static v4_heat h;
static v4_cell rom[16];
/* ROM words 0..: "7 ;" at ROM+0, then a cell holding 42 at ROM+8 */
static void build_rom(void)
{
v4_asm ra;
unsigned i;
v4_node_reset(&scratch);
v4_asm_begin(&ra, &scratch, 0);
v4_asm_lit(&ra, 7);
v4_asm_op(&ra, V4_OP_SEMI);
CHECK(v4_asm_ok(&ra), "the ROM's code assembles");
for (i = 0; i < 16; i++) rom[i] = scratch.mem[i];
rom[8] = 42;
}
int main(void)
{
v4_asm as;
long r;
build_rom();
v4_node_reset(&n);
v4_exec_reset(&es);
v4_heat_reset(&h);
CHECK(V4_ROM_BASE == (v4_cell)V4_NODE_WORDS, "the ROM starts where RAM ends");
CHECK(v4_node_load(&n, V4_ROM_BASE) == 0, "no ROM attached: nothing there");
v4_node_rom_attach(&n, rom, 16);
CHECK(v4_node_load(&n, V4_ROM_BASE) == rom[0], "the ROM reads");
CHECK(v4_node_load(&n, V4_ROM_BASE + 16) == 0, "past the ROM's words: nothing");
/* RAM 16: call the ROM's word, then return */
v4_asm_begin(&as, &n, 16);
v4_asm_branch(&as, V4_OP_CALL, V4_ROM_BASE);
v4_asm_op(&as, V4_OP_SEMI);
CHECK(v4_asm_ok(&as), "a call into the ROM assembles");
r = v4_test_call(&n, &es, &h, 16, 100);
CHECK(r > 0, "the call returns");
CHECK(n.ds.depth == 1 && n.ds.t == 7, "code in the ROM runs: depth %u T %ld", n.ds.depth, (long)n.ds.t);
/* RAM 32: fetch the ROM's cell 8 through A */
v4_dstack_reset(&n.ds);
v4_asm_begin(&as, &n, 32);
v4_asm_lit(&as, V4_ROM_BASE + 8);
v4_asm_op(&as, V4_OP_BANG_A);
v4_asm_op(&as, V4_OP_FETCH_A);
v4_asm_op(&as, V4_OP_SEMI);
CHECK(v4_asm_ok(&as), "a fetch from the ROM assembles");
r = v4_test_call(&n, &es, &h, 32, 100);
CHECK(r > 0 && n.ds.depth == 1 && n.ds.t == 42, "a data fetch reads the ROM: T %ld", (long)n.ds.t);
/* RAM 48: store 99 into the ROM's cell 8 through B */
v4_dstack_reset(&n.ds);
v4_asm_begin(&as, &n, 48);
v4_asm_lit(&as, V4_ROM_BASE + 8);
v4_asm_op(&as, V4_OP_BANG_B);
v4_asm_lit(&as, 99);
v4_asm_op(&as, V4_OP_STORE_B);
v4_asm_op(&as, V4_OP_SEMI);
CHECK(v4_asm_ok(&as), "a store into the ROM assembles");
r = v4_test_call(&n, &es, &h, 48, 100);
CHECK(r < 0, "a store into the ROM does not return");
CHECK(n.fault_kind == V4_FAULT_ADDRESS && n.fault_addr == V4_ROM_BASE + 8,
"it is an address fault at the ROM's address: kind %u addr %ld", n.fault_kind, (long)n.fault_addr);
CHECK(v4_node_load(&n, V4_ROM_BASE + 8) == 42, "and the ROM is unchanged");
/* C code's store does nothing there either */
v4_node_store(&n, V4_ROM_BASE + 8, 99);
CHECK(v4_node_load(&n, V4_ROM_BASE + 8) == 42, "v4_node_store leaves the ROM alone");
/* a reset detaches it, as it does every device */
v4_node_reset(&n);
CHECK(v4_node_load(&n, V4_ROM_BASE) == 0, "a reset detaches the ROM");
v4_node_rom_attach(&n, rom, 16);
CHECK(v4_node_load(&n, V4_ROM_BASE) == rom[0], "and the owner attaches it again");
/* more words than the range holds are refused: nothing attached */
v4_node_rom_attach(&n, rom, V4_ROM_WORDS + 1u);
CHECK(v4_node_load(&n, V4_ROM_BASE) == 0, "a ROM larger than the range is not attached");
printf("test_host_rom_range: %d checks, %d failures\n", checks, failures);
return failures != 0;
}