Add host command setting GPIO drive strength

examples/BUILD

@@ -243,6 +243,7 @@ cc_binary(
         "//protocol:authz_record",
         "//protocol:chipinfo",
         "//protocol:console",
+        "//protocol:gpio_drive_strength",
         "//protocol:controlled_storage",
         "//protocol:dfu_check",
         "//protocol:dfu_hostcmd",

examples/htool.c

@@ -60,6 +60,7 @@
 #include "protocol/chipinfo.h"
 #include "protocol/console.h"
 #include "protocol/controlled_storage.h"
+#include "protocol/gpio_drive_strength.h"
 #include "protocol/hello.h"
 #include "protocol/opentitan_version.h"
 #include "protocol/progress.h"
@@ -759,6 +760,33 @@ int htool_controlled_storage_delete(const struct htool_invocation* inv) {
   return libhoth_controlled_storage_delete(dev, slot);
 }
 
+static int command_set_gpio_drive_strength(const struct htool_invocation* inv) {
+  struct libhoth_device* dev = htool_libhoth_device();
+  if (!dev) {
+    return -1;
+  }
+
+  uint32_t pad;
+  uint32_t strength;
+
+  if (htool_get_param_u32(inv, "pad", &pad) ||
+      htool_get_param_u32(inv, "strength", &strength)) {
+    return -1;
+  }
+
+  if (strength > MAX_GPIO_DRIVE_STRENGTH) {
+    fprintf(stderr, "Drive strength can only be up to 15.\n");
+    return -1;
+  }
+
+  if (pad > 255) {
+    fprintf(stderr, "Pad must be a single byte.\n");
+    return -1;
+  }
+
+  return libhoth_set_gpio_drive_strength(dev, (uint8_t)pad, (uint8_t)strength);
+}
+
 static int command_hello(const struct htool_invocation* inv) {
   struct libhoth_device* dev = htool_libhoth_device();
   if (!dev) {
@@ -1565,6 +1593,25 @@ static const struct htool_cmd CMDS[] = {
                                                {}},
         .func = htool_controlled_storage_delete,
     },
+    {
+        .verbs = (const char*[]){"gpio", "set_drive_strength", NULL},
+        .desc = "Set GPIO drive strength",
+        .params =
+            (const struct htool_param[]){
+                {.type = HTOOL_FLAG_VALUE,
+                 .ch = 'p',
+                 .name = "pad",
+                 .default_value = NULL,
+                 .desc = "The GPIO pad to configure. (0-8 => IOA0-8 | 9-21 => "
+                         "IOB0-12 | 22-34 => IOC0-12 | 35-46 => IOR0-13)"},
+                {.type = HTOOL_FLAG_VALUE,
+                 .ch = 's',
+                 .name = "strength",
+                 .default_value = NULL,
+                 .desc = "The drive strength to set from 0 - 15"},
+                {}},
+        .func = command_set_gpio_drive_strength,
+    },
     {
         .verbs = (const char*[]){"hello", NULL},
         .desc = "A test function to send and receive an integer",

protocol/BUILD

@@ -406,6 +406,16 @@ cc_test(
     ],
 )
 
+cc_library(
+    name = "gpio_drive_strength",
+    srcs = ["gpio_drive_strength.c"],
+    hdrs = ["gpio_drive_strength.h"],
+    deps = [
+        ":host_cmd",
+        "//transports:libhoth_device",
+    ],
+)
+
 cc_library(
     name = "opentitan_version",
     srcs = ["opentitan_version.c"],

protocol/gpio_drive_strength.c

@@ -0,0 +1,31 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "protocol/gpio_drive_strength.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "protocol/host_cmd.h"
+
+int libhoth_set_gpio_drive_strength(struct libhoth_device* const dev,
+                                    const uint8_t pad, const uint8_t strength) {
+  const struct hoth_request_set_gpio_drive_strength request = {
+      .pad = pad,
+      .strength = strength,
+  };
+  return libhoth_hostcmd_exec(dev, HOTH_CMD_SET_GPIO_DRIVE_STRENGTH,
+                              /*version=*/0, &request, sizeof(request),
+                              /*response=*/NULL, /*response_size=*/0, NULL);
+}

protocol/gpio_drive_strength.h

@@ -0,0 +1,41 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef _LIBHOTH_PROTOCOL_GPIO_DRIVE_STRENGTH_H_
+#define _LIBHOTH_PROTOCOL_GPIO_DRIVE_STRENGTH_H_
+
+#include <stdint.h>
+
+#include "protocol/host_cmd.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define HOTH_CMD_SET_GPIO_DRIVE_STRENGTH 0x3E56
+#define MAX_GPIO_DRIVE_STRENGTH 0xF
+
+struct hoth_request_set_gpio_drive_strength {
+  uint8_t pad;
+  uint8_t strength;
+} __hoth_align1;
+
+int libhoth_set_gpio_drive_strength(struct libhoth_device* dev, uint8_t pad,
+                                    uint8_t strength);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // _LIBHOTH_PROTOCOL_GPIO_DRIVE_STRENGTH_H_

protocol/meson.build

@@ -24,7 +24,8 @@ protocol_srcs = [
     'dfu_check.c',
     'firmware_update.c',
     'util.c',
-    'console.c'
+    'console.c',
+    'gpio_drive_strength.c'
 ]
 
 incdir = libhoth_include_dirs