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[usb_host] Extract cold path from loop(), replace std::string with buffer API

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Extract the USB_CLIENT_OPEN state handling into handle_open_state_() to
keep loop() hot path small (~112 B vs 440 B before). Replace
get_descriptor_string() std::string return with caller-provided
fixed-size buffer via std::span to eliminate heap allocation during
device connection.
This commit is contained in:
J. Nick Koston
2026-02-12 10:25:53 -06:00
parent e12ed08487
commit 9c72c022b2
2 changed files with 65 additions and 56 deletions
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1
esphome/components/usb_host/usb_host.h
View File

@@ -148,6 +148,7 @@ class USBClient : public Component {
EventPool<UsbEvent, USB_EVENT_QUEUE_SIZE> event_pool;
protected:
void handle_open_state_();
TransferRequest *get_trq_(); // Lock-free allocation using atomic bitmask (multi-consumer safe)
virtual void disconnect();
virtual void on_connected() {}

120
esphome/components/usb_host/usb_host_client.cpp
View File

@@ -9,6 +9,7 @@
#include <cinttypes>
#include <cstring>
#include <atomic>
#include <span>
namespace esphome {
namespace usb_host {
@@ -142,18 +143,22 @@ static void usb_client_print_config_descriptor(const usb_config_desc_t *cfg_desc
} while (next_desc != NULL);
}
#endif
static std::string get_descriptor_string(const usb_str_desc_t *desc) {
char buffer[256];
// USB string descriptors: bLength (uint8_t, max 255) includes 2-byte header.
// Loop iterates bLength/2 times (max 127), each writing at most 1 ASCII char, plus null terminator.
static constexpr size_t DESC_STRING_BUF_SIZE = 128;
static const char *get_descriptor_string(const usb_str_desc_t *desc, std::span<char, DESC_STRING_BUF_SIZE> buffer) {
if (desc == nullptr)
return "(unspecified)";
char *p = buffer;
for (int i = 0; i != desc->bLength / 2; i++) {
char *p = buffer.data();
char *end = p + buffer.size() - 1;
for (int i = 0; i != desc->bLength / 2 && p < end; i++) {
auto c = desc->wData[i];
if (c < 0x100)
*p++ = static_cast<char>(c);
}
*p = '\0';
return {buffer};
return buffer.data();
}
// CALLBACK CONTEXT: USB task (called from usb_host_client_handle_events in USB task)
@@ -259,60 +264,63 @@ void USBClient::loop() {
ESP_LOGW(TAG, "Dropped %u USB events due to queue overflow", dropped);
}
switch (this->state_) {
case USB_CLIENT_OPEN: {
int err;
ESP_LOGD(TAG, "Open device %d", this->device_addr_);
err = usb_host_device_open(this->handle_, this->device_addr_, &this->device_handle_);
if (err != ESP_OK) {
ESP_LOGW(TAG, "Device open failed: %s", esp_err_to_name(err));
this->state_ = USB_CLIENT_INIT;
break;
}
ESP_LOGD(TAG, "Get descriptor device %d", this->device_addr_);
const usb_device_desc_t *desc;
err = usb_host_get_device_descriptor(this->device_handle_, &desc);
if (err != ESP_OK) {
ESP_LOGW(TAG, "Device get_desc failed: %s", esp_err_to_name(err));
this->disconnect();
} else {
ESP_LOGD(TAG, "Device descriptor: vid %X pid %X", desc->idVendor, desc->idProduct);
if (desc->idVendor == this->vid_ && desc->idProduct == this->pid_ || this->vid_ == 0 && this->pid_ == 0) {
usb_device_info_t dev_info;
err = usb_host_device_info(this->device_handle_, &dev_info);
if (err != ESP_OK) {
ESP_LOGW(TAG, "Device info failed: %s", esp_err_to_name(err));
this->disconnect();
break;
}
this->state_ = USB_CLIENT_CONNECTED;
ESP_LOGD(TAG, "Device connected: Manuf: %s; Prod: %s; Serial: %s",
get_descriptor_string(dev_info.str_desc_manufacturer).c_str(),
get_descriptor_string(dev_info.str_desc_product).c_str(),
get_descriptor_string(dev_info.str_desc_serial_num).c_str());
if (this->state_ == USB_CLIENT_OPEN) {
this->handle_open_state_();
}
}
void USBClient::handle_open_state_() {
int err;
ESP_LOGD(TAG, "Open device %d", this->device_addr_);
err = usb_host_device_open(this->handle_, this->device_addr_, &this->device_handle_);
if (err != ESP_OK) {
ESP_LOGW(TAG, "Device open failed: %s", esp_err_to_name(err));
this->state_ = USB_CLIENT_INIT;
return;
}
ESP_LOGD(TAG, "Get descriptor device %d", this->device_addr_);
const usb_device_desc_t *desc;
err = usb_host_get_device_descriptor(this->device_handle_, &desc);
if (err != ESP_OK) {
ESP_LOGW(TAG, "Device get_desc failed: %s", esp_err_to_name(err));
this->disconnect();
return;
}
ESP_LOGD(TAG, "Device descriptor: vid %X pid %X", desc->idVendor, desc->idProduct);
if (desc->idVendor != this->vid_ || desc->idProduct != this->pid_) {
if (this->vid_ != 0 || this->pid_ != 0) {
ESP_LOGD(TAG, "Not our device, closing");
this->disconnect();
return;
}
}
usb_device_info_t dev_info;
err = usb_host_device_info(this->device_handle_, &dev_info);
if (err != ESP_OK) {
ESP_LOGW(TAG, "Device info failed: %s", esp_err_to_name(err));
this->disconnect();
return;
}
this->state_ = USB_CLIENT_CONNECTED;
char buf_manuf[DESC_STRING_BUF_SIZE];
char buf_product[DESC_STRING_BUF_SIZE];
char buf_serial[DESC_STRING_BUF_SIZE];
ESP_LOGD(TAG, "Device connected: Manuf: %s; Prod: %s; Serial: %s",
get_descriptor_string(dev_info.str_desc_manufacturer, buf_manuf),
get_descriptor_string(dev_info.str_desc_product, buf_product),
get_descriptor_string(dev_info.str_desc_serial_num, buf_serial));
#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
const usb_device_desc_t *device_desc;
err = usb_host_get_device_descriptor(this->device_handle_, &device_desc);
if (err == ESP_OK)
usb_client_print_device_descriptor(device_desc);
const usb_config_desc_t *config_desc;
err = usb_host_get_active_config_descriptor(this->device_handle_, &config_desc);
if (err == ESP_OK)
usb_client_print_config_descriptor(config_desc, nullptr);
const usb_device_desc_t *device_desc;
err = usb_host_get_device_descriptor(this->device_handle_, &device_desc);
if (err == ESP_OK)
usb_client_print_device_descriptor(device_desc);
const usb_config_desc_t *config_desc;
err = usb_host_get_active_config_descriptor(this->device_handle_, &config_desc);
if (err == ESP_OK)
usb_client_print_config_descriptor(config_desc, nullptr);
#endif
this->on_connected();
} else {
ESP_LOGD(TAG, "Not our device, closing");
this->disconnect();
}
}
break;
}
default:
break;
}
this->on_connected();
}
void USBClient::on_opened(uint8_t addr) {