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MUSB

musb(Mentor USB) Registers and embassy-usb-driver , usb-device Implementation.

The MUSBMHDRC (musb) is a USB 2.0 Multi-Point, Dual-Role Controller designed by Mentor Graphics Corp. It is widely used by various manufacturers in microcontrollers and SoCs, including companies like TI, MediaTek, Puya, Allwinner, and others.

This crate contains register information because some manufacturers modify register offsets or mask certain registers, making it challenging for PACs to handle these uniformly.

How to Identify a MUSB IP?

  • Registers start with POWER, FADDR (though not always at the beginning)
  • Most registers are 8-bit (some manufacturers group them into 32-bit, but it's usually clear they're composed of 8-bit registers)
  • An INDEX register exists, requiring setting before endpoint operations. EP0 registers are separate, other endpoints use TXCSRH, TXCSRL, RXCSRH, RXCSRL (or IN_CSR1, IN_CSR2, OUT_CSR1, OUT_CSR2)
  • Compare with block-peri-std to confirm register similarity

Known chips using MUSB IP

Manufacturer Chips (not fully listed) IP
Texas Instruments am335x,am1802, F2837xD, LM3S6911 musb**
Allwinner(全志) F1C100S, F133 musb phy ip
SiFli (思澈) SF32LB52x musb std*
beken (北科微 or 小博通) beken725x musb std*
essemi (东软载波微) ES32F027x musb std*
jieli (杰理) musb**
SPRD sp7862 musb**
MediaTek MT6735 musb**
Puya (普冉) py32f071, py32f403 musb mini*
STC (姚永平) stc8, stc32, ai8051u musb mini*

*: Not sure about the IP name

**: Further identification is needed

Usage

  • If your chip uses standard MUSB IP (and hasn't disabled features like Dynamic FIFO size configuration):

    You can use the std profile by enabling the builtin-std feature. This profile doesn't include a base_address, so it won't generate a UsbInstance (explained below).

    You can then set the number of endpoints using the endpoints-num-x feature (e.g., endpoints-num-8). The total FIFO size can be configured using the total-fifo-size-dword-x feature (e.g., total-fifo-size-dword-256 where 256 double-words = 2048 bytes) (TODO). Currently, endpoints-num-x and total-fifo-size-dword-x are not effective when the prebuild feature is enabled.

  • If your chip's MUSB implementation differs significantly from the standard MUSB IP: You'll need to create a new profile. You can reference the PY32F07x profile example. Specific details will be covered below. If your register offsets or sizes differ from existing blocks and fieldsets, you'll need to add your specific blocks or fieldsets.

Features

embassy-usb-driver-impl: Enables embassy-usb-driver implementation.

usb-device-impl: Enables usb-device implementation.

Note: Only one of these two implementations can be enabled at a time.

prebuild(on by default): Uses pre-generated PAC (Peripheral Access Crate).

builtin-xxxx: Uses builtin profile.

endpoints-num-x: Specifies the number of endpoints. Only needs to be set when this information is not provided in the profile.

total-fifo-size-dword-x: Specifies the total FIFO size. Only needs to be set when using dynamic FIFO sizing and this information is not provided in the profile.

defmt, log: Enables debug logging.

Available Built-in Profiles

These built-in profiles are used via Cargo features (see below), with only one selectable:

  • builtin-py32f07x
  • builtin-py32f403
  • builtin-std (excludes base_address and endpoints_num)

These profiles include register descriptions, number of endpoints, etc.

Prebuild

Pre-generated Rust register code for each builtin is available in src/prebuild, eliminating the need to rerun build scripts generating these contents.

Note: endpoints-num-x and total-fifo-size-dword-x are not effective when the prebuild feature is enabled.

When you don't use the prebuild feature, you need to install:

cargo install --git https://github.com/embedded-drivers/yaml2pac --rev 0b96c69a30557214ceb16bd7429ab9ca1c52fc7e --locked
# On the Stable toolchain
rustup component add rustfmt
# On the Nightly toolchain
rustup component add rustfmt --toolchain nightly

Integrate this crate into a HAL crate

Examples

Example: py32-hal/src/usb.rs · py32-rs/py32-hal

embassy-usb: py32-hal/examples/py32f072

usb-device: py32-hal/examples/usbd-f072

Instance

Every struct in this crate has a generic parameter T: MusbInstance.

pub trait MusbInstance: 'static {
    fn regs() -> regs::Usb;
}

If the profile contains a base_address field, you can directly use:

let musb_driver = musb::Driver::<musb::UsbInstance>(new);

musb::UsbInstance is a struct that has already implemented the MusbInstance trait based on base_address.

If not, you need to create this type:

pub struct UsbInstance;
impl musb::MusbInstance for UsbInstance {
    fn regs() -> musb::regs::Usb {
        unsafe { musb::regs::Usb::from_ptr((0x40005c00) as _ ) }
    }
}

Driver

This crate includes a MusbDriver that has methods from embassy_usb_driver::Driver but doesn't implement it. The intention is for HAL libraries to create a Driver that wraps MusbDriver to handle platform-specific peripheral initialization. Please refer to the Examples section.

Profiles & Registers

Each manufacturer's SVD or manual exhibits significant register name variations, despite functional consistency. This crate uses standard MUSB register names.

The crate describes registers using YAML, with these register description files manually maintained. It then leverages chiptool and yaml2pac to generate register operation functions. These operations can be found in the build.rs file.

To write a profile, please refer to existing profiles and serialization-related data types

Available Replacements

These replacements are automatically generated from profile contents and can be used in register description YAML files.

  • ENDPOINTS_NUM

    profile.endpoints_num OR endpoints-num-x feature (e.g. endpoints-num-8)。

  • FIFO_REG_BIT_SIZE (does not change the offset)

    profile.reg_bit_size.fifo

    Note: This does not change the offset.

  • INTR_REG_BIT_SIZE (does not change the offset)

    profile.reg_bit_size.intr

Contribute

If you have any questions or uncertainties, feel free to create an Issue or start a Discussion.

TODOs:

  • Support Dynamic FIFO Size
  • Support dual packet buffer
  • Support SiFli SF32BL52
  • Other Chips
  • better support for standard musb
  • host mode