feat: DAP error detection and recovery in Step 3 TCL

- TCL now checks for ARM core visibility before attempting flow
- If ARM cores are not found (DAP APB transaction error):
  * Logs WARNING with target list
  * Attempts SLCR system reset (0xF8000200)
  * Reconnects after recovery attempt
- DAP errors detected in xsct output and logged to GUI log
- Result message shows 'DAP error — board needs power cycle'

src/bitstream_programmer.py

@@ -589,30 +589,56 @@ def full_bitstream_program(
     if callback:
         callback("start", "Initializing Zynq via JTAG (FSBL override)...")
 
-    tcl = "\n".join([
+    # Build TCL with DAP error recovery
+    tcl_lines = [
         'puts "INFO: Starting Zynq initialization via JTAG override..."',
         "connect",
         "after 500",
-        # 1. Select ARM Core 0
+    ]
+
+    # DAP error check — if ARM cores not visible, try recovery
+    tcl_lines.extend([
+        '# Check for DAP errors and attempt recovery',
+        'set target_list [targets]',
+        'set has_arm 0',
+        'foreach t $target_list { if {[regexp -nocase {arm|cortex} $t]} { set has_arm 1 } }',
+        'if {!$has_arm} {',
+        '  puts "WARNING: ARM cores not found — DAP may be in error state"',
+        '  # Show DAP status for logging',
+        '  foreach t $target_list { puts "  TARGET: $t" }',
+        '  # Attempt to recover by reinitializing via DAP',
+        '  catch { targets 1 }',
+        '  after 500',
+        '  # If DAP is accessible, try writing to system reset register',
+        '  catch {',
+        '    puts "Attempting SLCR system reset..."',
+        '    mwr 0xF8000200 0x00000001',
+        '    after 1000',
+        '    disconnect',
+        '    after 1000',
+        '    connect',
+        '    after 500',
+        '  }',
+        '}',
+        '',
+    ])
+
+    # Core flow
+    tcl_lines.extend([
         'targets -set -nocase -filter {name =~ "arm*#0"}',
-        # 2. Reset processor (bypass BootROM Flash boot)
         'puts "INFO: Resetting processor (Bypassing BootROM Flash boot)..."',
         "rst -processor",
         "after 500",
-        # 3. Download FSBL to OCM
         'puts "INFO: Downloading FSBL..."',
         'dow "%s"' % fsbl_path,
-        # 4. Run FSBL for hardware init (clocks, DDR, MIO)
         'puts "INFO: Running FSBL for hardware initialization..."',
         "con",
         "after 2000",
         "stop",
         'puts "INFO: Hardware initialization completed."',
-        # 5. Program PL bitstream
         'puts "INFO: Downloading Bitstream..."',
         'fpga -f "%s"' % bit_path,
         "after 1000",
-        # 6. Back to ARM Core 0, download and run app
         'targets -set -nocase -filter {name =~ "arm*#0"}',
         'puts "INFO: Downloading Application ELF..."',
         'dow "%s"' % elf_path,
@@ -622,6 +648,8 @@ def full_bitstream_program(
         "exit",
     ])
 
+    tcl = "\n".join(tcl_lines)
+
     with tempfile.NamedTemporaryFile(
         mode="w", suffix=".tcl", delete=False
     ) as tf:
@@ -644,6 +672,14 @@ def full_bitstream_program(
 
         success = result.returncode == 0 and "SUCCESS" in output
 
+        # Detect DAP errors for logging
+        dap_errors = [l for l in output.split("\n") if "DAP" in l and "error" in l.lower()]
+        if dap_errors:
+            if callback:
+                for e in dap_errors:
+                    callback("error", f"DAP: {e.strip()[:120]}")
+            success = False
+
         if callback:
             callback(
                 "complete" if success else "error",
@@ -654,13 +690,21 @@ def full_bitstream_program(
             BitstreamResult(
                 step="bitstream",
                 success=success,
-                message="Bitstream loaded" if success else "Combined flow failed",
+                message=(
+                    "DAP error — board needs power cycle"
+                    if dap_errors else
+                    "Bitstream loaded" if success else "Combined flow failed"
+                ),
                 output=output[:4000],
             ),
             BitstreamResult(
                 step="elf",
                 success=success,
-                message="ELF executed" if success else "Combined flow failed",
+                message=(
+                    "DAP error — board needs power cycle"
+                    if dap_errors else
+                    "ELF executed" if success else "Combined flow failed"
+                ),
                 output=output[:4000],
             ),
         ]