Remove the device-ID one-shot: it made Swiss see no adapter at all

id_phase was set at reset and cleared permanently by the GC's first NCRA reset,
after which a command-space read of register 0 returned 0x00000000.  Swiss
calls EXI_GetID from bba_exists() AND again from bba_requires_init(), long
after init, and matches the result against EXI_MX98730EC_ID -- so with the
one-shot spent no case matched and Swiss reported NO ADAPTER, not a broken one.
Running gc_bba_test was enough to spend it, so the adapter would "disappear"
after any test session.

The justification in the comment was wrong.  It claimed the fast path would
otherwise hijack address 0 so the GC could never read NCRA back -- but NCRA is
REGISTER space (0x80/0xC0 header) while the fast path requires byte 0 == 0x00,
i.e. COMMAND space.  They were never ambiguous, and no driver reads command
register 0 for anything else (libogc2 reads 0x01/0x03/0x0B/0x0F, Swiss 0x03).
Real hardware answers EXI_GetID whenever asked; that is how EXI enumerates
devices.

id_arm is now tied high, and the id_phase output, the FFSynchronizer that
crossed it into the pin domain, and the BBATop wiring are all gone.  The port
stays only so the PHASE_METER build can disarm the fast path, which would
otherwise send ID bytes instead of its constant 0x80.

bba_top T1b reads the device ID AFTER an NCRA reset, which T1 (before any
reset) structurally cannot catch.  Mutation-tested: disarming the fast path
returns 00 00 00 00 for both, exactly what Swiss saw.

gc_bba_test: the ID tests no longer skip.  A wrong ID is a FAILURE again, with
no iface_alive() discrimination and no ordering requirement between suites --
the ID is readable at any point in a run.  g_ncra_reset_done and iface_alive()
are removed outright rather than left as a dead flag.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -88,18 +88,9 @@ Reset/control, EXI integrity (speed sweep `ok=[1,1,1,1,1,1]`, per-speed dump
 clean at all six indices, raw reg dump `0x17` in slot 0), Ethernet, and
 SPRAM/DMA. The EXI front end runs at the real 27 MHz hardware rate.
 
-(The ID tests report SKIP, not FAIL, once `id_phase` has been consumed —
-reflash the FPGA to restore it. They decide that from the hardware, via
-`iface_alive()`: HIPR and NWAYS are hardwired and independent of `id_phase`, so
-if both read correctly the EXI path is fine and only a spent `id_phase` can
-explain a wrong answer at address 0.
-
-⚠️ The `g_ncra_reset_done` flag alone is NOT sufficient, and this bites every
-time a build is delivered over the wire: netboot replaces the DOL and restarts
-the app with the flag clear, while the FPGA keeps running with `id_phase`
-already spent by the previous run. The app then queries address 0, gets NCRA
-back — correct behaviour — and called it a FAILURE. Software state cannot stand
-in for hardware state across a self-update.)
+(The ID tests simply PASS or FAIL now, in any order, at any point in a run —
+see "The device ID is answerable at any time" below. The old SKIP machinery,
+`iface_alive()` and `g_ncra_reset_done` are all gone.)
 
 **Timing closes on EVERY seed (re-measured 2026-10-10).** `python -m
 exi_bba.synth --seeds 8`:
@@ -563,9 +554,11 @@ until byte 0 has been decoded — which is the latency in question.
 constant and belongs to the physical interface, not the register file, and
 `byte 0 == 0x00` identifies the query exactly (bit 7 clear = command space,
 bit 6 clear = read, reg 0). `SPIMode3Slave` recognises it and answers
-`04 02 02 00` from the EXI clock domain with **no CDC at all**. The only thing
-it needs from `sync` is `id_phase`, a single bit that changes once, crossed
-with an `FFSynchronizer`.
+`04 02 02 00` from the EXI clock domain with **no CDC at all** — and since
+2026-10-10 it needs nothing from `sync` either: `id_arm` is tied high (the
+`id_phase` bit and its `FFSynchronizer` are gone). The only remaining use of
+the port is the `PHASE_METER` build, which disarms the fast path so the
+constant `0x80` is not replaced by ID bytes.
 
 The register file's ID path was **removed**, not kept as a fallback: left in,
 it pushes bytes a 2-byte header has too few pops to drain — exactly how an
@@ -745,12 +738,38 @@ not clear it (RST_N floats to its pull-up while the FPGA is unconfigured). A
 12 V power cycle is required. Check ETH_3V3 and GC_ON (U12 gates the W5100 rail
 off GC_ON) before suspecting gateware.
 
-**`id_phase` is a ONE-SHOT.** The device ID is returned for reads of address 0
-only until the first NCRA write with the reset bit, which clears `id_phase`
-permanently (`bba_register_file.py:330`); after that address 0 reads back NCRA.
-This is correct — it matches the GC's init order — but it means a re-run of any
-probe that already issued an NCRA reset will read `00 00 00 00` for the device
-ID and look broken. Reconfigure the FPGA (`iceprog -t` is enough) to restore it.
+### ✅ The device ID is answerable AT ANY TIME (one-shot removed 2026-10-10)
+
+`id_phase` **used to be a one-shot**: set at reset and cleared permanently by
+the GC's first NCRA write with the reset bit, after which a command-space read
+of register 0 returned `0x00000000`. That is now gone — `id_arm` is tied high
+and the register file has no `id_phase` output.
+
+⚠️ **The one-shot broke Swiss outright, which is how it was caught.** Swiss
+calls `EXI_GetID` from `bba_exists()` *and* again from `bba_requires_init()`,
+long after init has run:
+
+```c
+if ((location & LOC_SERIAL_PORT_1) && EXI_GetID(EXI_CHANNEL_0, EXI_DEVICE_2, &id)) {
+    switch (id) { case EXI_MX98730EC_ID: ...
+```
+
+With the one-shot spent, that read returns `0x00000000`, no case matches, and
+Swiss reports **no adapter at all** — not a broken one, absent. Running
+`gc_bba_test` first was enough to spend it, so the adapter would "disappear"
+after any test session.
+
+**The old justification was wrong.** The comment claimed the fast path would
+otherwise "hijack address 0 forever so the GC could never read NCRA back".
+NCRA is **register space** (`0x80`/`0xC0` header); the fast path requires
+byte 0 == `0x00`, i.e. **command space**. They were never ambiguous, and no
+driver reads command register 0 for anything else (libogc2 reads
+`0x01`/`0x03`/`0x0B`/`0x0F`, Swiss reads `0x03`). Real hardware answers
+`EXI_GetID` whenever asked — that is how EXI enumerates devices.
+
+Test: `bba_top` **T1b** reads the device ID *after* an NCRA reset, which T1
+(before any reset) structurally cannot catch. Mutation-tested: disarming the
+fast path returns `00 00 00 00` for both, exactly what Swiss saw.
 
 Two bring-up gotchas, both cost real debugging time:
 - **The master must sample MISO during the CLK-LOW phase.** The FPGA drives MISO

exi_bba/bba_register_file.py

@@ -107,13 +107,6 @@ class BBARegisterFile(Elaboratable):
         # (DMA) bulk reads, not just ≤4-byte immediate transfers.
         self.cs_active = Signal()
 
-        # One-shot: set at reset, cleared by the GC's first NCRA reset.  While
-        # set, a command-space read of register 0 returns the device ID -- but
-        # the REPLY is produced by SPIMode3Slave's fast path, not here, because
-        # a 2-byte command header leaves too little time for a round trip
-        # through both byte FIFOs.  This output is what arms that path.
-        self.id_phase  = Signal(init=1)
-
         # ── Ring-overflow protection (RBFI) ───────────────────────────────
         # RRP out to RXFrameAssembler so it can tell how much of the ring is
         # still unread and DROP frames instead of overwriting them.
@@ -350,9 +343,6 @@ class BBARegisterFile(Elaboratable):
         # length for any driver that skips TWD.
         txdata_cnt = Signal(16)
 
-        # True until first NCRA reset write: return device ID on addr=0 reads
-        id_phase = self.id_phase
-
         # Per-byte SPRAM read handshake (register-read path): sp_req marks a
         # request in flight; drain_ctr counts the read-phase dummy bytes.
         sp_req    = Signal()
@@ -603,11 +593,29 @@ class BBARegisterFile(Elaboratable):
             with m.State("CHDR_1"):
                 with m.If(self.rx_rdy):
                     m.d.comb += self.rx_en.eq(1)
-                    # The device-ID query (command reg 0 while id_phase) is
-                    # answered by SPIMode3Slave, not here: pushing anything
-                    # for it would leave stale bytes in the tx FIFO that a
-                    # 2-byte header has too few pops to drain.
-                    with m.If(~is_write & (cmd_reg == 0) & id_phase):
+                    # The device-ID query (command space, read, reg 0) is
+                    # answered by SPIMode3Slave's fast path, not here: pushing
+                    # anything for it would leave stale bytes in the tx FIFO
+                    # that a 2-byte header has too few pops to drain.
+                    #
+                    # ⚠️ NO LONGER GATED ON A ONE-SHOT.  This used to be
+                    # `& id_phase`, a bit cleared by the GC's first NCRA
+                    # reset, after which the device stopped identifying
+                    # itself.  Real hardware answers EXI_GetID whenever the
+                    # GC asks -- that is how EXI enumerates devices -- and
+                    # Swiss calls it from bba_exists() and again from
+                    # bba_requires_init() long after init.  With the one-shot
+                    # spent, EXI_GetID returned 0x00000000 and Swiss reported
+                    # NO ADAPTER AT ALL.
+                    #
+                    # The old justification was that the fast path would
+                    # "hijack address 0 forever so the GC could never read
+                    # NCRA back".  That was wrong: NCRA is REGISTER space
+                    # (0x80/0xC0 header) and this path requires byte 0 ==
+                    # 0x00, i.e. COMMAND space.  They were never ambiguous,
+                    # and no driver reads command register 0 for anything
+                    # else (libogc2 reads 0x01/0x03/0x0B/0x0F, Swiss 0x03).
+                    with m.If(~is_write & (cmd_reg == 0)):
                         m.next = "DEVID"
                     with m.Elif(is_write):
                         m.next = "CMD_WRITE"
@@ -661,7 +669,6 @@ class BBARegisterFile(Elaboratable):
                             with m.If(self.rx_data[0]):
                                 m.d.sync += r_ncra[0].eq(0)  # RESET self-clears
                                 m.d.sync += ncra_rst_pulse.eq(1)
-                                m.d.sync += id_phase.eq(0)
                                 # An NCRA reset resets the RX ring, so the
                                 # pointers the GC reads MUST follow -- the
                                 # assembler's own write pointer goes back to

exi_bba/bba_top.py

@@ -190,7 +190,6 @@ class BBATop(Elaboratable):
             # EXI outputs
             self.exi_miso.eq(cap.spi_miso),
             self.exi_miso_next.eq(cap.miso_next),
-            cap.id_phase.eq(reg.id_phase),
             # Ring-overflow protection: the assembler needs the GC's read
             # pointer to know what it must not overwrite, and reports a
             # dropped frame back as RBFI (IR[7]).
@@ -626,6 +625,25 @@ if __name__ == "__main__":
         await ctx.delay(HP * (2000))   # let W5100 init run
         await exi_write(ctx, 0x00, [0x08])    # NCRA SR bit → enable RX
         await ctx.delay(HP * (HALF * 2))
+
+        # T1b: the device ID STILL ANSWERS after an NCRA reset.
+        #
+        # It used to be a one-shot: `id_phase` was cleared by the GC's first
+        # NCRA reset, after which a command-space read of reg 0 returned
+        # 0x00000000.  Real hardware answers EXI_GetID whenever asked -- that
+        # is how EXI enumerates devices -- and Swiss calls it from
+        # bba_exists() AND again from bba_requires_init(), long after init.
+        # With the one-shot spent, Swiss reported NO ADAPTER AT ALL.
+        #
+        # T1 above reads the ID before any reset, so it cannot catch this;
+        # the reset two lines up is what makes this check meaningful.
+        dev2 = await exi_devid(ctx)
+        print(f"T1b device ID after NCRA reset: {[f'0x{b:02X}' for b in dev2]}")
+        if dev2 != [0x04, 0x02, 0x02, 0x00]:
+            errors.append(f"T1b device ID after NCRA reset: got {dev2} "
+                          f"- the one-shot is back, Swiss would see no adapter")
+        await ctx.delay(HP * (HALF * 2))
+
         ctx.set(dut.w5100_int_n, 0)           # W5100: a packet was received
         await ctx.delay(HP * (4000))   # let the W5100 RX + SPRAM write run
         ctx.set(dut.w5100_int_n, 1)

exi_bba/exi_capture.py

@@ -83,11 +83,6 @@ class ExiCapture(Elaboratable):
         self.spi_cs_n = Signal(init=1)
         self.spi_miso = Signal()
         self.miso_next = Signal(init=1)   # for an SB_IO output register
-        # Register-file id_phase (sync domain).  Crossed into exiclk so the
-        # bit engine can answer the device-ID query itself -- see the fast
-        # path in SPIMode3Slave.
-        self.id_phase  = Signal(init=1)
-
         # Core-facing RX read side
         self.rx_data = Signal(8)
         self.rx_rdy  = Signal()
@@ -133,12 +128,15 @@ class ExiCapture(Elaboratable):
         ]
 
         spi = SPIMode3Slave(phase_meter=self._phase_meter)
-        # id_phase is a slow single bit: it starts set and clears once, on the
-        # GC's first NCRA reset, which happens inside a register-space
-        # transaction with the clock running -- so it propagates well before
-        # the next transaction needs it.
-        m.submodules.id_sync = FFSynchronizer(self.id_phase, spi.id_arm,
-                                              o_domain="exiclk", init=1)
+        # The device-ID fast path is ARMED PERMANENTLY.  It used to be gated
+        # by the register file's `id_phase`, a one-shot cleared on the GC's
+        # first NCRA reset and crossed in here with an FFSynchronizer -- so
+        # after init the device stopped identifying itself and Swiss's
+        # EXI_GetID returned 0x00000000, i.e. "no adapter".  Real hardware
+        # answers EXI_GetID whenever asked.  `id_arm` stays a port because
+        # the PHASE_METER diagnostic build needs to turn the fast path off
+        # (it would otherwise send ID bytes instead of the constant 0x80).
+        m.d.comb += spi.id_arm.eq(0 if self._phase_meter else 1)
         m.submodules.spi = spi
 
         # RX bytes cross exiclk -> sync; TX bytes cross sync -> exififo_r.

gc_bba_test/source/tests.c

@@ -5,54 +5,31 @@
 #include <unistd.h>
 #include <ogc/lwp_watchdog.h>
 
-int g_ncra_reset_done = 0;
 
 static void msleep(u32 ms) { usleep(ms * 1000); }
 
 /* ───────────────────────── suite 1: identity ───────────────────────── */
 
-/* Is the EXI link demonstrably healthy apart from address 0?
+/* The device ID is answerable AT ANY TIME, so these tests no longer skip.
  *
- * Needed because `id_phase` is a ONE-SHOT in the FPGA, cleared by the first
- * NCRA reset, and g_ncra_reset_done only tracks resets THIS RUN of the test
- * app issued.  That flag is software state standing in for hardware state, and
- * the two come apart as soon as a build is delivered over the wire: netboot
- * replaces the DOL and restarts the app with the flag clear, while the FPGA
- * keeps running with id_phase already spent by the previous run.  The ID tests
- * then query address 0, get NCRA back -- correct behaviour -- and report a
- * FAILURE for it.  Reflashing the FPGA is the only thing that restores it.
+ * It used to be a one-shot in the FPGA -- `id_phase`, cleared by the GC's
+ * first NCRA reset -- so these tests had to guess whether a wrong answer meant
+ * a spent one-shot or a real fault, and they ran in a fixed order to get a
+ * reading at all.  That was a deviation from real hardware, which answers
+ * EXI_GetID whenever the GC asks (it is how EXI enumerates devices).  The
+ * deviation broke Swiss outright: it calls EXI_GetID from bba_exists() and
+ * again from bba_requires_init() long after init, and with the one-shot spent
+ * got 0x00000000, i.e. NO ADAPTER AT ALL.
  *
- * HIPR and NWAYS are hardwired constants in the register file and do not
- * depend on id_phase, so if BOTH read correctly the EXI path is fine and a
- * wrong answer at address 0 can only be a spent id_phase.  If they are wrong
- * too, something real is broken and the test must still fail. */
-static int iface_alive(void)
-{
-	return bba_r8(REG_HIPR)  == HIPR_PRESENT &&
-	       bba_r8(REG_NWAYS) == NWAYS_LINKUP;
-}
-
+ * With that removed, a wrong ID is simply a FAILURE again -- no skip, no
+ * iface_alive() discrimination, and no ordering requirement between suites. */
 static int t_devid(char *m, size_t n)
 {
 	u8 b[4];
 	int rc;
-	if (g_ncra_reset_done) {
-		snprintf(m, n, "skipped: id_phase is a one-shot; reflash/reset the FPGA");
-		return 2;
-	}
 	if ((rc = bba_devid(b)) < 0) { snprintf(m, n, "EXI error %d", rc); return 1; }
-	if (b[0]==0x04 && b[1]==0x02 && b[2]==0x02 && b[3]==0x00) {
-		snprintf(m, n, "%02X %02X %02X %02X (want 04 02 02 00)",
-		         b[0], b[1], b[2], b[3]);
-		return 0;
-	}
-	if (iface_alive()) {
-		snprintf(m, n, "%02X %02X %02X %02X: id_phase spent, reflash FPGA",
-		         b[0], b[1], b[2], b[3]);
-		return 2;
-	}
 	snprintf(m, n, "%02X %02X %02X %02X (want 04 02 02 00)", b[0], b[1], b[2], b[3]);
-	return 1;
+	return (b[0]==0x04 && b[1]==0x02 && b[2]==0x02 && b[3]==0x00) ? 0 : 1;
 }
 
 static int t_hipr(char *m, size_t n)
@@ -130,7 +107,6 @@ static int t_ncra_reset(char *m, size_t n)
 {
 	int i, v;
 	if (bba_w8(REG_NCRA, NCRA_RESET) < 0) { snprintf(m, n, "write failed"); return 1; }
-	g_ncra_reset_done = 1;
 	for (i = 0; i < 50; i++) {
 		v = bba_r8(REG_NCRA);
 		if (v < 0) { snprintf(m, n, "read failed"); return 1; }
@@ -269,14 +245,6 @@ static int t_raw_id(char *m, size_t n)
 	u8 b[8];
 	int i, at = -1, rc;
 	u16 h = 0x0000;
-	/* Fast path for a reset this run issued.  Note this flag can be STALE
-	 * (see iface_alive): it is clear after a netbooted update even though the
-	 * FPGA's id_phase is long gone, which is why the result is also checked
-	 * against iface_alive() below rather than trusted to this. */
-	if (g_ncra_reset_done) {
-		snprintf(m, n, "skipped: id_phase is a one-shot; reflash/reset the FPGA");
-		return 2;
-	}
 	if ((rc = begin_raw()) < 0) { snprintf(m, n, "EXI error %d", rc); return 1; }
 	EXI_Imm(BBA_EXI_CHAN, &h, 2, EXI_WRITE, NULL);
 	EXI_Sync(BBA_EXI_CHAN);
@@ -287,10 +255,7 @@ static int t_raw_id(char *m, size_t n)
 	snprintf(m, n, "%02X %02X %02X %02X %02X %02X %02X %02X | 0x04 %s%d",
 	         b[0],b[1],b[2],b[3],b[4],b[5],b[6],b[7],
 	         at < 0 ? "absent" : "at slot ", at < 0 ? 0 : at);
-	if (at == 0)
-		return 0;
-	/* Same discrimination as t_devid: a spent id_phase is not a fault. */
-	return iface_alive() ? 2 : 1;
+	return at == 0 ? 0 : 1;
 }
 
 /* ───────────────────────── suite 5: ethernet ───────────────────────── */
@@ -527,7 +492,6 @@ static int t_init_sequence(char *m, size_t n)
 			return 1;
 		}
 	}
-	g_ncra_reset_done = 1;
 	/* The sentinels must still read correctly afterwards -- if any write in
 	 * that list had been misdecoded, the most likely casualty is the state
 	 * these two report. */

gc_bba_test/source/tests.h

@@ -31,7 +31,6 @@ extern const int g_nsuites;
  * clears id_phase in the gateware, after which address 0 reads back NCRA.
  * That is correct behaviour (it matches the GC's own init order), but it
  * means the ID test can only pass once per console power cycle. */
-extern int g_ncra_reset_done;
 
 void tests_run_test(test_t *t);
 void tests_run_suite(suite_t *s);