WiFi - WiFiフローチャート

Wifi 送信

WiFiでのデータ送信
既にWiFiの初期化とチャンネル変更を済ませたものと仮定して書いています。

• (1) 送信の準備のために、TX ヘッダを MAC メモリ に合わせて 802.11 パケットにコピーします。(ハーフワード境界)
• (2) パケットの準備のために、MAC メモリ の開始位置のオフセットを取得します。2で割って、0x8000との論理和を取ります。- W_TXLOCレジスタのうち1つにこれを入れます。
• (3) ACKが受信されるまでのパケットの再送信のために、W_RETRLIMITのセットをします。 (7 もしくは、それに近い値をいれます)
• (4) パケットを送信します。W_TXLOC レジスタ に、W_TXCNTを使って値をセットします。
• (5) TX後に、W_TXSTAT から結果データを読み込むことができます。

     (ポーリングか割り込みを使って問い合わせることができます。)再送信を何回やったかを見つけるためと、パケットが ACK だった時。

上記は一番単純な方法でのやりかたです。

Wifi 受信

To receive data via wifi, you either need to handle the wifi received data interrupt, or you need to poll W_RXHWWRITECSR - whenever it is != W_RXREADCSR, there is a new packet. When there is a new packet, take the following approach:

(1) Calculate the length of the new packet (read "received frame length"
     which is +8 bytes from the start of the packet) - total frame length
     is (12 + received frame length) padded to a multiple of 4 bytes.
(2) Read the data out of the RX FIFO area (keep in mind it's a circular
     buffer and you may have to wrap around the end of the buffer)
(3) Set the value of W_RXREADCSR to the location of the next packet
     (add the length of the packet, and wrap around if necessary)

Keep in mind, W_RXREADCSR and W_RXHWWRITECSR must be multiplied by 2 to get a byte offset from the start of MAC memory.

Wifi チャンネル変更

You can set the channel to any channel number between 1 and 13 (inclusive) on the DS hardware. here's some pseudocode to do it:

read 3 bytes of flash starting at (0xF2+(channel-1)*6) to a temporary value
call RF_Write with the 3 bytes you just read (as a 0-padded long value)
read 3 bytes of flash starting at (0xF5+(channel-1)*6) to a temporary value
call RF_Write with the 3 bytes you just read (as a 0-padded long value)
delay a few milliseconds
call BB_Write with parameters 0x1E, and the byte in flash at 0x146+(channel-1)

Congrats, you are now ready to transmit/receive on whatever channel you picked.

ハードウェア TX ヘッダ

The TX header is a structure needed by the wifi hardware, it contains important information such as the length of the packet being sent and the rate at which to send (possibly other things too). The TX header is always 12 bytes, it immediately precedes the data to be sent, and should be put at the location that will be given to the register activating a transmission.
The TX header takes the following form: (entries are halfwords)
Offset Description

+0    Unknown (used by hardware)
+2    Unknown (used by hardware)
+4    Unknown (used by hardware)
+6    Unknown (used by hardware)
+8    Transmit rate (speed in megabits multiplied by 10)
       (1.0Mbit is 0x0A, 2.0Mbit is 0x14)
+10   Transmit length (bytes) transmits the data
       at +12 through +12+length-1 inclusive.

Important note! TX length includes the length of a 4-byte "FCS" (checksum) for the packet. The hardware generates the FCS for you, but you still must include it in the packet length. Also note that if the 802.11 WEP enabled bit is set in the header, the packet will be automatically encrypted via the wep algorithm - however, the software is responsible for providing the 4-byte IV block with the WEP key ID and the 24bit IV value. - ALSO, you must include the length of the *encrypted* FCS used in packets that have wep enabled (increase the tx length by another 4 bytes) - this value is calculated automaticly for you, but you are responsible for including it in the length of your packet (if you have data there, it'll be replaced by the FCS.)

ハードウェア RX ヘッダ

The RX header is an informational structure that provides needed information about a received packet. It is written right before the received packet data in the rx circular buffer. The RX header is always 12 bytes.
The RX header takes the following form: (entries are halfwords)
Offset Description

+0    Unknown (used by hardware)
+2    Unknown (used by hardware)
+4    Unknown (used by hardware)
+6    Unknown (used by hardware)
+8    Received frame length (bytes)
+10   RSSI Range (Bottom 8 bits are MAX RSSI, top 8 bits are MIN RSSI,
       during the receipt of the packet)

Important Note: Received frame lengths are always multiples of 4 bytes. While the actual header length + received frame length may be less, when incrementing the read cursor you must pad the length to a multiple of 4 bytes

XXX..............known (W) mirrors

 Read from (W)           Mirrors to
 070h W_BUF_WR_DATA      060h W_BUF_RD_DATA (passive mirror)
 158h W_BBSIOCNT         15Ch W_BBSIOREAD
 178h                    17Ch W_RFSIODATA2

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