Module usb 

USB-CDC-ACM device with esptool auto-reset support.

The Lolin S2 Mini has no USB-UART bridge, so esptool cannot toggle GPIO0/EN via physical DTR/RTS pins. Instead, the firmware exposes the native USB-OTG port as a CDC-ACM device and interprets the CDC control-line state the way the classic devkit reset sequence does:

DTR	RTS	Meaning	Action
1	0	IO0 low	set FORCE_DOWNLOAD_BOOT
0	1	EN low (reset)	software reset
0	0	idle	clear FORCE_DOWNLOAD_BOOT
1	1	transient	no-op

esptool’s --before usb-reset walk is (0,0) -> (1,0) -> (0,1) -> (0,0): the (1,0) state arms FORCE_DOWNLOAD_BOOT, then (0,1) resets into the ROM bootloader.

The flag lives in the RTC domain and survives software resets. The ROM bootloader does not clear it on entry — after a flash the chip would stay stuck in the bootloader forever (until power-on). inv flash therefore clears the flag itself after flashing (esptool write-reg 0x3F408128 0 0x1 through the stub) and then resets via the RTC watchdog, which boots the application.

The same task also drains the log ring from crate::logging over the CDC data endpoint, so inv monitor shows the firmware log output.

Constants

LOG_CHUNK 🔒

Log chunk size handed to the CDC endpoint (matches max_packet_size).

POLL_INTERVAL 🔒

Line-poll interval of the DTR/RTS state machine.

USB_PID 🔒

Espressif generic CDC-ACM product ID.

USB_VID 🔒

Espressif USB vendor ID (same as the ROM bootloader).

Statics

BOS_DESCRIPTOR 🔒

Buffer for the generated USB configuration descriptor.

CDC_STATE 🔒

Scratch buffer for USB control transfers.

CONFIG_DESCRIPTOR 🔒

Bulk OUT endpoint buffer for the CDC data endpoint.

CONTROL_BUF 🔒

Buffer for the generated USB BOS descriptor.

EP_OUT_BUFFER 🔒

The S2 peripheral types are invariant in their lifetime, which pins the USB driver to 'static; the embassy-usb buffers therefore must be 'static too. They are initialized exactly once at task start.

Functions

control_and_log 🔒

Runs the DTR/RTS state machine and drains the log ring into the host.

enter_bootloader 🔒

Resets into the ROM USB-CDC download mode (bootloader).

flush_logs 🔒

Copies pending log lines from the ring into the CDC endpoint until the ring is empty or the endpoint errors out. See control_and_log for the cancellation-safety argument.

set_force_download 🔒

Set or clear the ROM FORCE_DOWNLOAD_BOOT flag in RTC_CNTL_OPTION1.

task

Runs the USB-CDC-ACM device and the esptool reset protocol.