D3AA simulator

1 files changed, 29 insertions, 0 deletions

diff --git a/src/peripherals/avrdx-ccp.ts b/src/peripherals/avrdx-ccp.ts
new file mode 100644
index 0000000..a4f0370
--- /dev/null
+++ b/src/peripherals/avrdx-ccp.ts
@@ -0,0 +1,29 @@
+// CCP - Configuration Change Protection
+// When 0xD8 (IOREG) or 0x9D (SPM) is written to CCP, a 4-cycle window opens
+// during which protected registers can be written.
+
+import type { CPU } from 'avr8js/cpu/cpu';
+
+const ADDR = 0;
+
+const SPM  = 0x9D;
+const IOREG = 0xD8;
+
+export class AVRDxCCP {
+  private unlockedUntil = -Infinity;
+
+  constructor(private cpu: CPU, base: number) {
+    cpu.writeHooks[base + ADDR] = (value) => {
+      if (value === IOREG || value === SPM) {
+        // TODO: adjust for cycle scaling(?)
+        this.unlockedUntil = cpu.cycles + 4;
+      }
+      cpu.data[base + ADDR] = value;
+      return true;
+    };
+  }
+
+  isUnlocked(): boolean {
+    return this.cpu.cycles <= this.unlockedUntil;
+  }
+}