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Our PHY uses an explicitly declared repeating sequence of scrambling bytes (see ofdm_tx_supermimo_init.m).

Just to clarify- the question above (from 2011) is about the older OFDM Reference Design.

In the 802.11 Reference Design the Tx PHY scrambler has two modes.

In the first mode the scrambler state is not reset after a packet is transmitted. The end state from the previous Tx becomes the initial state for the next Tx. In a sense, the previous packet's length is the seed for the next packet's scrambler state. This is the default mode in the ref design.

The second mode resets the scrambler state on every Tx. This is useful for debugging if you need to generate identical waveforms for multiple transmissions of a given payload.

Hi,

Currently, I need the 802.11 Reference Design to operate in the second mode for my experiment.
How could I switch to the second mode?
(Just change the second bit of the REG_TX_Config to 1?
Can I set this bit in the C files by adding this line:
REG_SET_BITS(WLAN_TX_REG_CFG, WLAN_TX_REG_CFG_RESET_SCRAMBLING_PER_PKT);
in the function wlan_phy_init() in wlan_mac_low.c ?)

Also, just to make sure that I understand it correctly: If the 802.11 Reference Design is operating in the second mode, it will reset the scrambler state to the same seed (is it the "all ones" seed?) before each transmission and thus generates identical waveforms for the same payload. Is it correct? Will the waveform of ACKs also be identical?

Thanks,

Thank you very much for the clarify and the suggested consideration.

We have not implemented a wlan_exp command to control the scrambling mode. However there is a simple way to add this to the C code.

The wlan_exp node class defines a method node._set_low_param(param, values). This method acts as a "pipe" from wlan_exp to the code in CPU Low, bypassing any interpretation by CPU High. It should be used with care - it is dangerous to change state in CPU Low while the PHYs and DCF state machine are running. This pipe should only be used to change parameters that will not disrupt MAC/PHY state. Changing the Tx PHY scrambling mode is a good use of this method.

To enable scrambling mode control via the _set_low_param() method:
-Select a new param ID that does not overlap the existing IDs in wlan_mac_low.h

-Add your new param control code to the IPC message handler in wlan_mac_low.c using the new param ID.

-In Python call node._set_low_param(<new param ID>, <scrambling mode 0 or 1>)

For example:

//in wlan_mac_low.h
#define LOW_PARAM_TX_SCRAMBLER_MODE 0x1000

//in wlan_mac_low.c / case IPC_MBOX_LOW_PARAM: / case IPC_REG_WRITE_MODE:
case LOW_PARAM_TX_SCRAMBLER_MODE:
	if( ipc_msg_from_high_payload[1] == 1 ) {
		REG_SET_BITS(WLAN_TX_REG_CFG, WLAN_TX_REG_CFG_RESET_SCRAMBLING_PER_PKT); 
	} else {
		REG_CLEAR_BITS(WLAN_TX_REG_CFG, WLAN_TX_REG_CFG_RESET_SCRAMBLING_PER_PKT); 
	}
break;

The benefit of this approach is you can implement the wlan_exp -> CPU Low path without modifying any code in CPU High. You will still need to maintain your CPU Low code modifications across future updates of the Reference Design. But this is much easier than maintaining High and Low changes.