[opentitanlib] add DFT disabling strap config and workaround

DFT straps were put on the same pins as the console UART (IOC3 and 4).
This causes JTAG reliability issues in test unlocked states if we do
not pull the straps low when they should be sampled. This provides a
software workaround.

Signed-off-by: Tim Trippel <[email protected]>

sw/device/silicon_creator/manuf/lib/BUILD

@@ -313,6 +313,7 @@ cc_library(
         "//sw/device/lib/dif:flash_ctrl",
         "//sw/device/lib/dif:pinmux",
         "//sw/device/lib/dif:uart",
+        "//sw/device/lib/runtime:hart",
         "//sw/device/lib/runtime:log",
         "//sw/device/lib/runtime:print",
     ],

sw/device/silicon_creator/manuf/lib/ast_program.c

@@ -7,6 +7,7 @@
 #include "sw/device/lib/dif/dif_flash_ctrl.h"
 #include "sw/device/lib/dif/dif_pinmux.h"
 #include "sw/device/lib/dif/dif_uart.h"
+#include "sw/device/lib/runtime/hart.h"
 #include "sw/device/lib/runtime/log.h"
 #include "sw/device/lib/runtime/print.h"
 #include "sw/device/lib/testing/flash_ctrl_testutils.h"
@@ -88,6 +89,14 @@ status_t ast_program_init(bool verbose) {
 }
 
 status_t ast_program_config(bool verbose) {
+  // Add delay to synchronize DFT strap sampling with HyperDebug UART console
+  // swapping (since DFT straps use same UART pins as OpenTitan console).
+  // Note: this should match the delay time in
+  // `sw/host/opentitanlib/src/app/mod.rs:reset_target()`.
+  if (kDeviceType == kDeviceSilicon) {
+    busy_spin_micros(/*usec=*/5 * 1000);  // Wait 5ms.
+  }
+
   TRY(ast_program_init(verbose));
 
   // Read AST calibration values from flash.
@@ -97,6 +106,7 @@ status_t ast_program_config(bool verbose) {
       (kFlashInfoFieldAstCalibrationData.page * device_info.bytes_per_page) +
       kFlashInfoFieldAstCalibrationData.byte_offset;
   uint32_t ast_data[kFlashInfoAstCalibrationDataSizeIn32BitWords];
+  TRY(flash_ctrl_testutils_wait_for_init(&flash_state));
   TRY(flash_ctrl_testutils_read(&flash_state, byte_address,
                                 kFlashInfoFieldAstCalibrationData.partition,
                                 ast_data, kDifFlashCtrlPartitionTypeInfo,

sw/host/opentitanlib/src/app/config/hyperdebug_chipwhisperer.json

@@ -7,6 +7,16 @@
       "pull_mode": "PullUp",
       "alias_of": "CN10_29"
     },
+    {
+      "name": "DFT_STRAP0",
+      "mode": "Alternate",
+      "alias_of": "IOC3"
+    },
+    {
+      "name": "DFT_STRAP1",
+      "mode": "Alternate",
+      "alias_of": "IOC4"
+    },
     {
       "name": "IOA0",
       "alias_of": "CN8_6"
@@ -237,5 +247,22 @@
       "name": "console",
       "alias_of": "UART2"
     }
+  ],
+  "strappings": [
+    {
+      "name": "PRERESET_DFT_DISABLE",
+      "pins": [
+        {
+          "name": "DFT_STRAP0",
+          "mode": "PushPull",
+          "level": false
+        },
+        {
+          "name": "DFT_STRAP1",
+          "mode": "PushPull",
+          "level": false
+        }
+      ]
+    }
   ]
 }

sw/host/opentitanlib/src/app/mod.rs

@@ -193,6 +193,7 @@ pub struct I2cConfiguration {
 
 pub struct TransportWrapperBuilder {
     interface: String,
+    disable_dft_on_reset: bool,
     openocd_adapter_config: Option<PathBuf>,
     provides_list: Vec<(String, String)>,
     requires_list: Vec<(String, String)>,
@@ -211,6 +212,7 @@ pub struct TransportWrapperBuilder {
 // transport will have been computed from a number ConfigurationFiles.
 pub struct TransportWrapper {
     transport: Rc<dyn Transport>,
+    disable_dft_on_reset: Cell<bool>,
     openocd_adapter_config: Option<PathBuf>,
     provides_map: HashMap<String, String>,
     pin_map: HashMap<String, String>,
@@ -227,9 +229,10 @@ pub struct TransportWrapper {
 }
 
 impl TransportWrapperBuilder {
-    pub fn new(interface: String) -> Self {
+    pub fn new(interface: String, disable_dft_on_reset: bool) -> Self {
         Self {
             interface,
+            disable_dft_on_reset,
             openocd_adapter_config: None,
             provides_list: Vec::new(),
             requires_list: Vec::new(),
@@ -623,6 +626,7 @@ impl TransportWrapperBuilder {
         let i2c_conf_map = Self::consolidate_i2c_conf_map(&self.i2c_conf_map)?;
         let mut transport_wrapper = TransportWrapper {
             transport: Rc::from(transport),
+            disable_dft_on_reset: Cell::new(self.disable_dft_on_reset),
             openocd_adapter_config: self.openocd_adapter_config,
             provides_map,
             pin_map: self.pin_alias_map,
@@ -666,6 +670,11 @@ impl TransportWrapperBuilder {
 }
 
 impl TransportWrapper {
+    pub fn ignore_dft_straps_on_reset(&self) -> Result<()> {
+        self.disable_dft_on_reset.set(false);
+        Ok(())
+    }
+
     /// Returns a `Capabilities` object to check the capabilities of this
     /// transport object.
     pub fn capabilities(&self) -> Result<crate::transport::Capabilities> {
@@ -923,17 +932,24 @@ impl TransportWrapper {
     }
 
     pub fn reset_target(&self, reset_delay: Duration, clear_uart_rx: bool) -> Result<()> {
-        let reset_strapping = self.pin_strapping("RESET")?;
         log::info!("Asserting the reset signal");
-        reset_strapping.apply()?;
+        if self.disable_dft_on_reset.get() {
+            self.pin_strapping("PRERESET_DFT_DISABLE")?.apply()?;
+        }
+        self.pin_strapping("RESET")?.apply()?;
         std::thread::sleep(reset_delay);
         if clear_uart_rx {
             log::info!("Clearing the UART RX buffer");
             self.uart("console")?.clear_rx_buffer()?;
         }
         log::info!("Deasserting the reset signal");
-        reset_strapping.remove()?;
-        std::thread::sleep(reset_delay);
+        self.pin_strapping("RESET")?.remove()?;
+        if self.disable_dft_on_reset.get() {
+            std::thread::sleep(Duration::from_millis(5));
+            // We remove the DFT strapping after waiting some time, as the DFT straps should have been
+            // sampled by then and we can resume our desired pin configuration.
+            self.pin_strapping("PRERESET_DFT_DISABLE")?.remove()?;
+        }
         Ok(())
     }
 }

sw/host/opentitanlib/src/backend/mod.rs

@@ -30,6 +30,13 @@ pub struct BackendOpts {
     #[arg(long, default_value = "")]
     pub interface: String,
 
+    /// Whether to disable DFT with a strapping config during reset. Only required in TestUnlocked*
+    /// LC states activate the JTAG RV TAP. This is required since the DFT straps share the console
+    /// UART pins, that hyperdebug tries to pull high. In mission mode states this should be set to
+    /// false, as DFT straps are not sampled here.
+    #[arg(long)]
+    pub disable_dft_on_reset: bool,
+
     /// USB Vendor ID of the interface.
     #[arg(long, value_parser = u16::from_str)]
     pub usb_vid: Option<u16>,
@@ -73,7 +80,7 @@ pub enum Error {
 /// Creates the requested backend interface according to [`BackendOpts`].
 pub fn create(args: &BackendOpts) -> Result<TransportWrapper> {
     let interface = args.interface.as_str();
-    let mut env = TransportWrapperBuilder::new(interface.to_string());
+    let mut env = TransportWrapperBuilder::new(interface.to_string(), args.disable_dft_on_reset);
 
     for conf_file in &args.conf {
         process_config_file(&mut env, conf_file.as_ref())?

sw/host/provisioning/orchestrator/ot_device.py

@@ -59,6 +59,7 @@ def cp_provision(self, require_confirmation=True):
                 "sram_cp_provision_fpga_cw310_rom_with_fake_keys.elf")
         else:
             platform_flags = """--interface=hyper310 \
+--disable-dft-on-reset \
 --openocd=third_party/openocd/build_openocd/bin/openocd \
 --openocd-adapter-config=external/openocd/tcl/interface/cmsis-dap.cfg"""
             elf = elf_path.format("sram_cp_provision_silicon_creator.elf")
@@ -135,6 +136,7 @@ def ft_provision(self, ecc_priv_keyfile, require_confirmation=True):
 
             platform_bazel_flags = "--//signing:token=//signing/tokens:nitrokey"
             platform_harness_flags = """--interface=hyper310 \
+--disable-dft-on-reset \
 --openocd=third_party/openocd/build_openocd/bin/openocd \
 --openocd-adapter-config=external/openocd/tcl/interface/cmsis-dap.cfg"""
 

sw/host/tests/manuf/provisioning/ft/src/main.rs

@@ -179,6 +179,9 @@ fn main() -> Result<()> {
         }
     };
 
+    // Once we are in a mission mode, we no longer need to provide a DFT strapping sequence on
+    // every reset, as DFT is no longer enabled in mission modes.
+    transport.ignore_dft_straps_on_reset()?;
     run_ft_personalize(
         &transport,
         &opts.init,