The basic unit of data transfer over MII and powerline is the IEEE 802.3 Ethernet frame. On output, the host must encapsulate each Ethernet frame as shown below before serial transmission to the QCA7000. The QCA7000 strips off the serial header and footer and forwards the frame over powerline.
Table 8.1. SPI Transmit Frame
Allocate a 1528-byte buffer to accommodate the largest outgoing serial packet and pad with NUL bytes. Write SOF, compute and write FL, copy the outgoing frame then write EOF. Serially transmit FL + 12 buffer bytes to the QCA7000.
| Offset | Length | Symbol | Description |
|---|---|---|---|
| 0x0000 | 4 | SOF |
Start Of Frame. Must be 0xAAAAAAAA.
|
| 0x0004 | 2 | FL |
The Ethernet frame length in little endian format. The frame starts at offset 0x0008 here and includes all fields up to but excluding EOF. The minimum is 60. The maximum is 1518 if VLAN is omitted and 1522 if not.
|
| 0x0006 | 2 | RSVD |
Must be 0x0000. Reserved to ensure 4-byte frame alignment.
|
| 0x0008 | 6 | DA | Destination address. |
| 0x000E | 6 | SA | Source address. This must not be the MAC address of the powerline device. This must be the MAC address of the local host serial interface as assigned by the SP or UART driver. The PLC device and the associated host interface must have different MAC address. |
| 0x0014 | 4 | VLAN | Virtual LAN tag. This field may be omitted. |
| 0x0018 | 2 | ET |
Ethertype. This field starts at offset 0x0014 if VLAN is omitted.
|
| 0x001A | 42 to 1500 | BODY |
Frame body. This field starts at offset 0x0016 and ranges from 46 to 1500 bytes if VLAN is omitted.
|
| 0x004A to 0x05F8 | 4 | EOF |
End Of Frame. Must be 0x5555. This field starts at offset 0x0008 plus FL.
|
Table 8.2. SPI Receive Frame
The SPI read frame occurs in response to a read interrupt generated by the QCA7000. The host must acknowledge a read interrupt and service it by reading and acting on QCA7000 SPI register values. For incoming frames, the host reads the 32-bit overall packet length reported by the QCA7000 then read that many bytes, stripping off the serial header and footer and forwarding the Ethernet frame to the host.
Allocate a 1532-byte buffer to accomodate the largest incoming serial packet. Read LEN to determine the size of the incoming serial packet. Read LEN bytes into the buffer. Beware that LEN is a multiple of 4-bytes so there may be a few trailing NUL bytes in buffer.
| Offset | Length | Symbol | Description |
|---|---|---|---|
| 0x0000 | 4 | LEN | Hardware generated packet length. This field is only generated for SPI packets, not the UART packets. |
| 0x0004 | 4 | SOF |
Start Of Frame. Must be 0xAAAAAAAA.
|
| 0x0008 | 2 | FL |
Ethernet frame length in little endian format. The frame starts at offset 0x000C here and includes all fields up to but excluding EOF. The minimum length is 60. The maximum is 1518 if VLAN is omitted and 1522 if not.
|
| 0x000A | 2 | RSVD |
Must be 0x0000. Reserved to ensure 4-byte frame alignment.
|
| 0x000C | 6 | DA | Destination address. |
| 0x0012 | 6 | SA | Source address. This must not be the MAC address of the powerline device. This must be the MAC address of the local host serial interface as assigned by the SP or UART driver. The PLC device and the associated host interface must have different MAC address. |
| 0x0018 | 4 | VLAN | Virtual LAN tag. This field may be omitted. |
| 0x001C | 2 | ET |
Ethertype. This field starts offset 0x0018 if VLAN is omitted.
|
| 0x001E | 42 to 1500 | BODY |
Frame body. This field starts at offset 0x001A and ranges from 46 to 1500 bytes if VLAN is omitted.
|
| 0x004A to 0x05F8 | 4 | EOF |
End Of Frame. Must be 0x5555. This field starts at offset 0x000C plus FL.
|