Module ip_mac_tx_bkoff_g
Block Diagram of ip_mac_tx_bkoff_g
Overview
Name |
Direction |
Type |
Description |
|---|---|---|---|
pi_reset |
input |
wire logic |
Global Hardware/Software reset (active low) |
pi_g_clock |
input |
wire logic |
Transmit GMII/MII 125/25/2.5 MHz clock (from Clock Manager, gated clock) |
pi_f_clock |
input |
wire logic |
Transmit GMII/MII 125/25/2.5 MHz clock (from Clock Manager, free clock) |
po_en_clock |
output |
var reg |
Transmit GMII/MII 125/25/2.5 MHz clock gated clock enable |
pi_bk_reset |
input |
wire logic |
Backoff interface Backoff counter reset command |
pi_bk_start |
input |
wire logic |
Backoff algorithm start command |
pi_half_duplex |
input |
wire logic |
Operating Half Duplex mode |
pi_hd_fc_enable |
input |
wire logic |
Half-Duplex Flow Control enable |
po_bk_done |
output |
var reg |
Backoff done indication |
Always Blocks
- always @ ( posedge pi_f_clock or negedge pi_reset )
Clock Gating Module
# |
Current State |
Next State |
Condition |
|---|---|---|---|
1 |
`BK_IDLE |
`BK_DONE |
[(!(~ pi_reset) && (pi_bk_start == 1’b1))] |
2 |
`BK_DONE |
`BK_IDLE |
[(!(~ pi_reset) && (bk_ended == slot_cnt && pi_hd_fc_enable == 1’b0)), (!(~ pi_reset) && !(bk_ended == slot_cnt && pi_hd_fc_enable == 1’b0) && (pi_hd_fc_enable == 1’b1))] |
Instances
- ip_emac_topip_emac_top
- mac_topip_mac_top_g
- mac_tx_topip_mac_tx_top_g
tx_bkoff
When a transmission attempt has terminated due to a collision, it is retried by the transmitting CSMA/CD sublayer until either it is successful or a maximum number of attempts have been made and all have terminated due to collisions. Note that all attempts to transmit a given frame are completed before any subsequent outgoing frames are transmitted. The scheduling of the retransmissions is determined by a controlled randomization process called truncated binary exponential backoff.
At the end of enforcing
a collision (jamming), the CSMA/CD sublayer delays before attempting to retransmit the frame. The delay is an integer multiple of 512 bit time slot. The number of slot times to delay before the nth retransmission attempt is chosen as a uniformly distributed random integer r in the range:
-1 < r < 2 power k, where k = min (n, 10)
If all n attempts limit fails, this event is reported as an error. Algorithms used to generate the integer r should be designed to minimize the correlation between the numbers generated by any two stations at any given time.
Note: The values given above define the most aggressive behavior that a station may exhibit in attempting to retransmit after a collision. In the course of implementing the retransmission scheduling procedure, a station may introduce extra delays that will degrade its own throughput, but in no case may a station retransmission scheduling result in a lower average delay between retransmission attempts than the procedure defined above.