fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM by Finder16 · Pull Request #11770 · RT-Thread/rt-thread · GitHub

拉取/合并请求描述：(PR description)

为什么提交这份PR (why to submit this PR)

With RT_USB_DEVICE_CDC and RT_USING_SERIAL_V2 both enabled, _function_enable() assigned the embedded rx_ringbuffer to serial.serial_rx:

data->serial.serial_rx = &data->rx_ringbuffer;

Serial V2 reads that pointer as a struct rt_serial_rx_fifo *. Because rt_ringbuffer is the first member of rt_serial_rx_fifo, ring-buffer access happened to work, while rx_cpt, rx_cpt_index and rx_timeout landed on the members that follow rx_ringbuffer inside struct vcom, corrupting tx_rbp. The layout shifts again when RT_SERIAL_USING_DMA is enabled, which inserts dma_ping_rb ahead of those fields.

Serial V2 already owns the receive FIFO: dev_serial_v2.c allocates it with rt_malloc() on open and releases it with rt_free() on close. The assignment therefore also overwrote the FIFO allocated at open time, and made the close path call rt_free() on memory inside struct vcom that was never dynamically allocated. The problem becomes reachable once the USB host configures the CDC device.

你的解决方案是什么 (what is your solution)

Remove the data->serial.serial_rx = &data->rx_ringbuffer; assignment from _function_enable(), so the RX FIFO that Serial V2 allocated on open stays intact.
In _ep_out_handler(), under RT_USING_SERIAL_V2, cast serial.serial_rx to struct rt_serial_rx_fifo * and push the received data into rx_fifo->rb, guarded against RT_NULL for the case where the serial device has not been opened yet. This matches rt_hw_serial_isr(), which reports RX_IND from serial_rx->rb.
In _vcom_getc(), drain the same FIFO under RT_USING_SERIAL_V2.
The Serial V1 path is left unchanged in the #else branches, so data->rx_ringbuffer is still used when RT_USING_SERIAL_V2 is not defined.

No API or Kconfig change is involved. The diff is limited to components/legacy/usb/usbdevice/class/cdc_vcom.c (+23 / -4).

请提供验证的bsp和config (provide the config and bsp)

BSP: Not board-specific. The change is in the common component
components/legacy/usb/usbdevice/class/cdc_vcom.c, which is shared by every BSP that
provides a USB device controller. It was not verified on physical hardware. Verification
was done by code review, struct-layout analysis of struct vcom versus
struct rt_serial_rx_fifo, and build checks. Testing on a board with a USB device
controller and RT_USB_DEVICE_CDC + RT_USING_SERIAL_V2 enabled is very welcome.
.config: RT_USING_SERIAL_V2, RT_USB_DEVICE, RT_USB_DEVICE_CDC
action: https://github.com/Finder16/rt-thread/actions/runs/33252216932
(qemu-vexpress-a9, sourcery-arm, branch fix/vcom-serial-v2-rx-fifo, result: success)

Note: no BSP in the tree enables RT_USB_DEVICE_CDC together with RT_USING_SERIAL_V2 in
its default .config, so cdc_vcom.c is not compiled by the BSP build CI. The linked run
only confirms that the tree still builds with this change applied. Review of the USB CDC
path itself, and testing on hardware with a USB device controller, would be appreciated.

贡献者 (Contributors)

This issue was analyzed and reported together with:

Ijae Kim (ijk5201@psu.edu)
Myeonghun Pak (mhun512@gmail.com)
Yuho Choi (yqc5929@psu.edu)
Taegyu Kim (tgkim@psu.edu)

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

已经仔细查看过代码改动的对比 Already check the difference between PR and old code
代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
代码是高质量的 Code in this PR is of high quality
已经使用clang-format 源码格式化工具确保格式符合RT-Thread代码规范 This PR has been formatted with clang-format and complies with RT-Thread code specification
如果是新增bsp, 已经添加ci检查到.github/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

With RT_USB_DEVICE_CDC and RT_USING_SERIAL_V2 both enabled, _function_enable assigned the embedded rx_ringbuffer to serial.serial_rx. Serial V2 reads that pointer as a struct rt_serial_rx_fifo, whose first member is a rt_ringbuffer, so ring-buffer access happened to work while rx_cpt, rx_cpt_index and rx_timeout landed on the following members of struct vcom, corrupting tx_rbp. The layout shifts again with RT_SERIAL_USING_DMA, which inserts dma_ping_rb ahead of those fields. Serial V2 already owns the receive FIFO: dev_serial_v2.c allocates it with rt_malloc on open and releases it with rt_free on close, so the assignment also made rt_free run on memory inside struct vcom. Drop the assignment and read the FIFO Serial V2 owns. rt_hw_serial_isr reports RX_IND from serial_rx->rb, so the endpoint handler now fills that ring buffer and _vcom_getc drains it. The Serial V1 path is unchanged. Fixes RT-Thread#11739 Signed-off-by: Jaeyeong Lee <lee@jaeyeong.cc>

All committers have signed the CLA.

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流（如果格式化CI运行失败）。
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在 branch 输入框填写 PR 分支 fix/vcom-serial-v2-rx-fifo
Enter PR branch fix/vcom-serial-v2-rx-fifo in the branch field
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📌 Code Review Assignment

🏷️ Tag: components

Reviewers: @Maihuanyi

Changed Files (Click to expand)

components/legacy/usb/usbdevice/class/cdc_vcom.c

📊 Current Review Status (Last Updated: 2026-09-12 07:57 CST)

⌛ @Maihuanyi Pending Review

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建议添加 rx_bufsz == 0 的轮询接收路径，因为在打开设备前将 config.rx_bufsz 配为 0，并使用 RT_SERIAL_RX_BLOCKING，Serial V2 会进入轮询模式，不分配 serial_rx。

if (data->serial.config.rx_bufsz == 0)
{
    rt_ringbuffer_put(&data->rx_ringbuffer, data->ep_out->buffer, size);
}

MemBrowse Memory Report

at32f415-start

ROM: .text +32 B (+0.0%, 65,400 B / 262,144 B, total: 25% used)

esp32-c3

iram0_2_seg: .flash.text +16 B (+0.0%, 229,594 B / 8,388,576 B, total: 3% used)

gd32105r-start

CODE: .text +32 B (+0.0%, 69,316 B / 262,144 B, total: 26% used)

hc32f334

FLASH: .text +32 B (+0.0%, 99,528 B / 131,072 B, total: 76% used)

hpmicro-hpm5301evklite

XPI0: .text -24 B (-0.0%, 124,968 B / 1,048,576 B, total: 12% used)

infineon-psoc6

flash: .text +32 B (+0.0%, 116,172 B / 262,144 B, total: 44% used)

k230

SRAM: .eh_frame +1,160 B, .sbss +8 B, .text +4,272 B (+0.5%, 1,128,507 B / 268,300,288 B, total: 0% used)

loongson-ls1cdev

Code: .text +56 B (+0.0%, 363,304 B)

nuvoton-m487

CODE: .text +8 B (+0.0%, 356,024 B / 524,288 B, total: 68% used)

qemu-virt64-aarch64

Code: .eh_frame +736 B, .text +6,272 B (+0.7%, 1,077,220 B)

raspberry-pico-rp2040

FLASH: .text +32 B (+0.0%, 114,136 B / 2,097,152 B, total: 5% used)

renesas-ra2l1

FLASH: .text -20 B (-0.0%, 98,256 B / 262,144 B, total: 37% used)

simulator

Code: .rela.dyn -408 B, .rodata +32 B, .text -65 B (-0.0%, 2,672,695 B)
Data: .data -576 B (-0.0%, 1,609,028 B)

stm32f407-rt-spark

CODE: .text +32 B (+0.0%, 85,796 B / 1,048,576 B, total: 8% used)

stm32l475-atk-pandora-llvm

ROM: .text +32 B (+0.0%, 83,460 B / 524,288 B, total: 16% used)

wch-ch32v208w-r0

FLASH: .text +32 B (+0.0%, 159,952 B / 491,520 B, total: 33% used)
No memory changes detected for:
nordic-nrf51822
nxp-lpc1114
x86
xuantie-e901plus

Signed-off-by: Jaeyeong Lee <lee@jaeyeong.cc>

github-actions Bot added the Component label Aug 29, 2026

Rbb666 reviewed Sep 7, 2026

View reviewed changes

fix[usb]: support VCOM polling receive with Serial V2

ec20f9f

Signed-off-by: Jaeyeong Lee <lee@jaeyeong.cc>

fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM by Finder16 · Pull Request #11770 · RT-Thread/rt-thread · GitHub

fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM - #11770

fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM#11770
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                       level = rt_hw_interrupt_disable();
+              #ifdef RT_USING_SERIAL_V2
+                      rx_fifo = (struct rt_serial_rx_fifo *)data->serial.serial_rx;

fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM by Finder16 · Pull Request #11770 · RT-Thread/rt-thread · GitHub

fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM - #11770

fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM#11770Finder16 wants to merge 2 commits intoRT-Thread:masterRT-Thread/rt-thread:masterfrom Finder16:fix/vcom-serial-v2-rx-fifoFinder16/rt-thread:fix/vcom-serial-v2-rx-fifoCopy head branch name to clipboard

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拉取/合并请求描述：(PR description)

为什么提交这份PR (why to submit this PR)

你的解决方案是什么 (what is your solution)

请提供验证的bsp和config (provide the config and bsp)

贡献者 (Contributors)

当前拉取/合并请求的状态 Intent for your PR

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🏷️ Tag: components

📊 Current Review Status (Last Updated: 2026-09-12 07:57 CST)

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fix[usb]: stop aliasing rt_ringbuffer as rt_serial_rx_fifo in VCOM#11770
Finder16 wants to merge 2 commits into
RT-Thread:masterfrom
Finder16:fix/vcom-serial-v2-rx-fifo

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