Livt.Usb

src/descriptors/DeviceDescriptorParser.lvt

namespace Livt.Usb.Descriptors

using Livt.Usb

/**
 * Bounded standard device descriptor validation. Feed an ordered prefix after Reset;
 * the first eight bytes establish EP0 geometry, all eighteen establish identity.
 */
component DeviceDescriptorParser
{
	// Initialized prefix and fixed standard descriptor bytes.
	data: byte[18]
	count: byte
	invalid: bool

	// Read-only observation; valid after IsValid succeeds.
	public identity: out logic[32]

	/**
	 * Exposes the retained descriptor identity without a scheduled return buffer.
	 */
	process Identity[]()
	{
		identity = ((data[8] as logic[32]) << 16) | ((data[9] as logic[32]) << 24)
			| (data[10] as logic[32]) | ((data[11] as logic[32]) << 8)
	}

	/**
	 * Discards old identity without exposing uninitialized array bytes.
	 */
	public fn Reset()
	{
		count = 0;
		invalid = false
	}

	/**
	 * Accepts up to eighteen ordered bytes; additional data invalidates the descriptor.
	 */
	public fn Feed(value: byte)
	{
		if (count == 18) { invalid = true } else {
			data[count as int] = value;
			count++
		}
	}

	/**
	 * Validates descriptor header and the packet sizes allowed for the observed speed.
	 */
	public fn HasPacketSize(speed: UsbSpeed) bool
	{
		if (invalid || count < 8 || data[0] != 18 || data[1] != 1) { return false }

		if (speed == UsbSpeed.Low) { return data[7] == 8 }

		return speed == UsbSpeed.Full && (data[7] == 8 || data[7] == 16 || data[7] == 32 || data[7] == 64)
	}

	/**
	 * Requires a full descriptor, a non-hub device and at least one configuration.
	 */
	public fn IsValid(speed: UsbSpeed) bool
	{
		return count == 18 && HasPacketSize(speed) && data[4] != 9 && data[17] != 0
	}

	/**
	 * Returns bMaxPacketSize0 after HasPacketSize succeeds.
	 */
	public fn GetPacketSize() int
	{
		return data[7] as int
	}

	/**
	 * Returns the vendor identifier after full validation.
	 */
	public fn GetVendor() int
	{
		return (data[8] as int) | ((data[9] as int) << 8)
	}

	/**
	 * Returns the product identifier after full validation.
	 */
	public fn GetProduct() int
	{
		return (data[10] as int) | ((data[11] as int) << 8)
	}
}