The following extracted from document Z-USB FX3 Boot Options.

USB Setup Packet

The FX3 bootloader decodes the SETUP packet that contains an 8-byte data structure defined in Table 4.

Table 4. Setup Packet

Byte Field Description
0 bmRequestType Request type: Bit7: Direction, Bit6–0: Recipient
1 bRequest This byte will be A0h for firmware download/upload vendor command.
2-3 wValue 16-bit value (little-endian format)
4-5 wIndex 16-bit value (little-endian format)
6-7 wLength Number of bytes
  • Note Refer to the USB 2.0 Specification for the bitwise explanation.

USB Chapter 9 and Vendor Command

The FX3 bootloader handles the commands in Table 5.

Table 5. USB Commands

bRequest Descriptions
00 GetStatus: Device, Endpoints, and Interface
01 ClearFeature: Device, Endpoints
02 Reserved: Returns STALL
03 SetFeature: Device, Endpoints
04 Reserved: Returns STALL
05 SetAddress: Handle in FX3 hardware
06 GetDescriptor: Devices’ descriptors in ROM
07 Reserved: Returns STALL
08h GetConfiguration: Returns internal value
09h SetConfiguration: Sets internal value
0Ah GetInterface:Rreturns internal value
0Bh SetInterface: Sets internal value
0Ch Reserved: Returns STALL
20h-9Fh Reserved: Returns STALL
A0h Vendor Commands: Firmware upload/download and so on
A1h-FFh Reserved: Returns STALL  

USB Vendor Command

The bootloader supports the A0h vendor command for firmware download and upload. The fields for the command are shown in Table 6 and Table 7

Table 6. Command Fields for Firmware Download

Byte Field Value Description
0 bmRequest Type 40h Request type: Bit7: Direction Bit6-0: Recipient.
1 bRequest A0h This byte will be A0 for firmware download/upload vendor command.
2-3 wValue AddrL(LSB) 16-bit value (little endian format)
4-5 wIndex AddrH(MSB) 16-bit value (little endian format)
6-7 wLength Count Number of bytes

Table 7. Command Fields for Firmware Upload | Byte | Field | Value | Description | |——|——-|——-|————-| | 0 | bmRequest Type | C0h | Request type: Bit7: Direction Bit6-0: Recipient. | 1 | bRequest | A0h | This byte will be A0 for firmware download/upload vendor command. | 2-3 | wValue | AddrL(LSB) | 16-bit value (little endian format) | 4-5 | wIndex | AddrH(MSB) | 16-bit value (little endian format) | 6-7 | wLength | Count | Number of bytes

Table 8. Command Fields for Transfer of Execution to Program Entry

Byte Field Value Description
0 bmRequest Type 40h Request type: Bit7: Direction Bit6-0: Recipient
1 bRequest A0h This byte will be A0 for firmware download/upload vendor command.
2-3 wValue AddrL(LSB) 32-bit Program Entry
4-5 wIndex AddrH(MSB) 32-bit Program Entry»16
6-7 wLength 0 This field must be zero.
  • In the transfer execution entry command, the bootloader will turn off all the interrupts and disconnect the USB.

Examples

Three examples of vendor command subroutines follow.

  1. Example 1. Vendor Command Write Data Protocol With 8-Byte Setup Packet 
    bmRequestType=0x40
bRequest = 0xA0;
wValue = (WORD)address;
wIndex = (WORD)(address>>16);
wLength = 1 to 4K-byte max

    This command will send DATA OUT packets with a length of transfer equal to wLength and a DATA IN Zero length packet.

  2. Example 2. Reading Bootloader Revision With Setup Packet 
    bmRequestType= 0xC0
bRequest = 0xA0;
wValue = (WORD)0x0020;
wIndex = (WORD)0xFFFF;
wLength = 4

    This command will issue DATA IN packets with a length of transfer equal to wLength and a DATA OUT Zero length packet.

  3. Example 3. Jump to Program Entry With 8-Byte Setup Packet (refer to Table 8.) 
    bmRequestType= 0x40
bRequest = 0xA0;
wValue = Program Entry (16-bit LSB)
wIndex = Program Entry >>16 (16-bit MSB)
wLength = 0

USB Device Descriptor for Vendor Command

Table 12. Interface Descriptor (Alt. Setting 0)

Offset Field Value Description
0 bLength 09h Length of this descriptor = 10 bytes(??)
1 bDescType 04h Descriptor type = Interface
2 bInterfaceNum 00h Zero-based index of this interface = 0
4 bAltSetting 00 Alternative Setting value = 0
5 bNumEndpoints 00 Only endpoint0
6 bInterfaceClass FFh Vendor Command Class
7 bInterfaceSubClass 00h  
8 bInterfaceProtocol 00h  
9 iInterface 00h None