From 07fec754eb5c0c68b50ee36ded86f57c9a590226 Mon Sep 17 00:00:00 2001
From: John Hardy <jh@lagado.com>
Date: Tue, 10 Feb 2026 00:50:02 +1100
Subject: [PATCH] Persist SD writes and extend SD SPI tests

---
 src/platforms/tec1g/runtime.ts               | 16 ++++++++++-
 src/platforms/tec1g/sd-spi.ts                |  8 ++++++
 tests/platforms/tec1g/sd-spi-runtime.test.ts |  3 ++
 tests/platforms/tec1g/sd-spi.test.ts         | 30 +++++++++++++++++++-
 4 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/src/platforms/tec1g/runtime.ts b/src/platforms/tec1g/runtime.ts
index adeda9a..6f6c30f 100644
--- a/src/platforms/tec1g/runtime.ts
+++ b/src/platforms/tec1g/runtime.ts
@@ -365,7 +365,21 @@ export function createTec1gRuntime(
     }
   }
   const sdSpi = sdEnabled
-    ? new SdSpi({ highCapacity: sdHighCapacity, ...(sdImage ? { image: sdImage } : {}) })
+    ? new SdSpi({
+        highCapacity: sdHighCapacity,
+        ...(sdImage ? { image: sdImage } : {}),
+        ...(sdImagePath && sdImage
+          ? {
+              onWrite: (image) => {
+                try {
+                  fs.writeFileSync(sdImagePath, image);
+                } catch {
+                  // Ignore persistence failures; runtime continues with in-memory image.
+                }
+              },
+            }
+          : {}),
+      })
     : null;
   let cartridgePresentDefault = config.cartridgeHex !== undefined;
   const state: Tec1gState = {
diff --git a/src/platforms/tec1g/sd-spi.ts b/src/platforms/tec1g/sd-spi.ts
index 9196851..49a9fac 100644
--- a/src/platforms/tec1g/sd-spi.ts
+++ b/src/platforms/tec1g/sd-spi.ts
@@ -13,6 +13,7 @@ export type SdSpiOptions = {
   csActiveLow?: boolean;
   highCapacity?: boolean;
   image?: Uint8Array;
+  onWrite?: (image: Uint8Array) => void;
 };
 
 const MOSI_BIT = 0x01;
@@ -37,6 +38,7 @@ export class SdSpi {
   private lastCommand: SdCommand | undefined;
   private outputQueue: number[] = [];
   private image: Uint8Array | null = null;
+  private onWrite?: (image: Uint8Array) => void;
   private pendingResponse: number[] | null = null;
   private delayBytes = 0;
   private appCommand = false;
@@ -60,6 +62,9 @@ export class SdSpi {
     this.csActiveLow = options.csActiveLow !== false;
     this.highCapacity = options.highCapacity !== false;
     this.image = options.image ?? null;
+    if (options.onWrite !== undefined) {
+      this.onWrite = options.onWrite;
+    }
   }
 
   /**
@@ -355,6 +360,9 @@ export class SdSpi {
           this.image[idx] = this.writeState.buffer[i] ?? 0x00;
         }
       }
+      if (this.onWrite) {
+        this.onWrite(this.image);
+      }
     }
     // Data response token: 0bxxx00101 = 0x05 (accepted).
     this.pendingResponse = [0x05, 0xff];
diff --git a/tests/platforms/tec1g/sd-spi-runtime.test.ts b/tests/platforms/tec1g/sd-spi-runtime.test.ts
index 688640f..1888281 100644
--- a/tests/platforms/tec1g/sd-spi-runtime.test.ts
+++ b/tests/platforms/tec1g/sd-spi-runtime.test.ts
@@ -155,5 +155,8 @@ describe('TEC-1G SD SPI runtime', () => {
     expect(readByte(rt)).toBe(0xde);
     expect(readByte(rt)).toBe(0xad);
     expect(readByte(rt)).toBe(0xbe);
+    sendCommand(rt, [0x4d, 0x00, 0x00, 0x00, 0x00, 0xff]);
+    expect(readResponse(rt)).toBe(0x00);
+    expect(readByte(rt)).toBe(0x00);
   });
 });
diff --git a/tests/platforms/tec1g/sd-spi.test.ts b/tests/platforms/tec1g/sd-spi.test.ts
index babbc4b..4e50ac9 100644
--- a/tests/platforms/tec1g/sd-spi.test.ts
+++ b/tests/platforms/tec1g/sd-spi.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, it } from 'vitest';
+import { describe, expect, it, vi } from 'vitest';
 import { SdSpi } from '../../../src/platforms/tec1g/sd-spi';
 
 const MOSI_BIT = 0x01;
@@ -179,6 +179,34 @@ describe('SdSpi', () => {
     expect(image[2]).toBe(0x56);
   });
 
+  it('invokes onWrite callback after CMD24 completes', () => {
+    const image = new Uint8Array(1024);
+    const payload = new Uint8Array(512);
+    payload[0] = 0xde;
+    payload[1] = 0xad;
+    payload[2] = 0xbe;
+    const onWrite = vi.fn();
+    const spi = new SdSpi({ csMask: CS_BIT, image, onWrite });
+    writeSpi(spi, 0x00);
+    sendCommand(spi, [0x77, 0x00, 0x00, 0x00, 0x00, 0x65]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x69, 0x40, 0x00, 0x00, 0x00, 0x77]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x77, 0x00, 0x00, 0x00, 0x00, 0x65]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x69, 0x40, 0x00, 0x00, 0x00, 0x77]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x58, 0x00, 0x00, 0x00, 0x00, 0xff]);
+    expect(readResponseByte(spi)).toBe(0x00);
+    writeDataBlock(spi, payload);
+    expect(readResponseByte(spi)).toBe(0x05);
+    expect(image[0]).toBe(0xde);
+    expect(image[1]).toBe(0xad);
+    expect(image[2]).toBe(0xbe);
+    expect(onWrite).toHaveBeenCalledTimes(1);
+    expect(onWrite).toHaveBeenCalledWith(image);
+  });
+
   it('responds to CMD13 with status', () => {
     const spi = new SdSpi({ csMask: CS_BIT });
     writeSpi(spi, 0x00);