Changes between Version 7 and Version 8 of 802.11/wlan_exp/app_notes/tutorial_token_mac/CPU_LOW

Timestamp:

Jul 9, 2015, 5:02:36 PM (9 years ago)

Author:

chunter

Comment:

--

802.11/wlan_exp/app_notes/tutorial_token_mac/CPU_LOW

@@ -202 +202 @@
                 pkt_buf_pending_tx = msg->arg0;
         }                       
-        break;
+break;
 }}}
 
@@ -285 +285 @@
 
 We will use {{{TX_PKT_BUF_TOKEN}}} as a hardcoded packet buffer index that is dedicated to transmitting our new token frames. {{{mac_frame_custom_token}}} is a struct that is our new custom token frame. It's format is inspired by 802.11 frames in order to allow nearby commercial Wi-Fi devices to decode and ignore these frames. We'll set the {{{frame_control_1}}} field to an invalid value to make ensure this.
+
+----
+
+Next, we will add two small functions to NoMAC that will act as packet constructors. They will create {{{mac_frame_custom_token}}} packets and fill the relevant values into the elements of that struct.
+
+{{{
+#!c
+
+#define MAC_FRAME_CTRL1_SUBTYPE_TOKEN_OFFER     (MAC_FRAME_CTRL1_TYPE_CTRL | 0x10)
+#define MAC_FRAME_CTRL1_SUBTYPE_TOKEN_RESPONSE  (MAC_FRAME_CTRL1_TYPE_CTRL | 0x20)
+
+int wlan_create_token_offer_frame(void* pkt_buf_addr, u8* address_ra, u8* address_ta, u16 duration, u32 res_duration) {
+        mac_frame_custom_token* token;
+        token = (mac_frame_custom_token*)(pkt_buf_addr);
+
+        token->frame_control_1 = MAC_FRAME_CTRL1_SUBTYPE_TOKEN_OFFER;
+        token->frame_control_2 = 0;
+        token->duration_id = duration;
+        memcpy(token->address_ra, address_ra, 6);
+        memcpy(token->address_ta, address_ta, 6);
+        token->res_duration_usec = res_duration;
+
+        //Include FCS in packet size (MAC accounts for FCS, even though the PHY calculates it)
+        return (sizeof(mac_frame_custom_token)+WLAN_PHY_FCS_NBYTES);
+}
+
+int wlan_create_token_response_frame(void* pkt_buf_addr, u8* address_ra, u8* address_ta, u16 duration, u32 res_duration) {
+        mac_frame_custom_token* token;
+        token = (mac_frame_custom_token*)(pkt_buf_addr);
+
+        token->frame_control_1 = MAC_FRAME_CTRL1_SUBTYPE_TOKEN_RESPONSE;
+        token->frame_control_2 = 0;
+        token->duration_id = duration;
+        memcpy(token->address_ra, address_ra, 6);
+        memcpy(token->address_ta, address_ta, 6);
+        token->res_duration_usec = res_duration;
+
+        //Include FCS in packet size (MAC accounts for FCS, even though the PHY calculates it)
+        return (sizeof(mac_frame_custom_token)+WLAN_PHY_FCS_NBYTES);
+}
+}}}
+
+Here we introduce the terminology of a "token offer" and a "token response." An offer is what an AP makes to a STA when it informs the STA it now can have the token and have access to the wireless medium. A response is what the STA responds to the offer with. This acts as a positive confirmation that the STA understands it has the token. Note that in both of these cases, the same {{{mac_frame_custom_token}}} struct is used. The distinction between these two types of frames is in the value of {{{frame_control_1}}}. The values of {{{MAC_FRAME_CTRL1_SUBTYPE_TOKEN_OFFER}}} and {{{MAC_FRAME_CTRL1_SUBTYPE_TOKEN_RESPONSE}}} are somewhat arbitrary. The definitions above are particularly useful because they are invalid in the 802.11 standard, so commercial Wi-Fi devices will likely just ignore them rather than falsely interpret them as some sort of standard 802.11 packet.
 
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