Frame Buffer Protection (Static/Dynamic)

There are different ways to safely keep the PSDU in the frame buffer without the risk of being overwritten by consecutively received frames.

Static Frame Buffer Protection

• PREAMBLE_DETECTOR_DISABLE
• SWITCHING_TO_PLL_ON

Dynamic Frame Buffer Protection

• SET_PROTECT_DYNAMIC
• GET_PROTECT_DYNAMIC

Parameters:

safe_mode

enable {1}/disable {0} dynamic frame buffer protection.

PREAMBLE_DETECTOR_DISABLE

One way to protect the frame buffer against overwriting is to disable the preamble detector. This can be achieved by writing value 1 to sub register SR_RX_PDT_DIS, e.g. right after the occurrence of one of the interrupts TRX_IRQ_RX_START (shown in the use case below) or TRX_IRQ_AMI. When the MCU is ready to process more frames, the preamble detector gets enabled by writing the value 0 to the sub register SR_RX_PDT_DIS.

Note:

Disabling the preamble detector can also be applied for monitoring the RF channel parameters (ED, RSSI, CCA) in order to avoid the reception of frames during the measurement.

Code example

    /* AT86RF212::[RX_ACTIVE] */
    /* TRX_IRQ_RX_START occurs here */
    trx_bit_write(SR_RX_PDT_DIS, 1);
    delay(tPSDU);
    frame = trx_frame_read();
    trx_bit_write(SR_RX_PDT_DIS, 0);
    /* AT86RF212::[RX_ACTIVE] */

SWITCHING_TO_PLL_ON

The frame buffer can also be protected against overwriting by setting the radio transceiver into state PLL_ON. This can be achieved by writing value CMD_PLL_ON to sub register SR_TRX_CMD, e.g. right after the occurrence of one of the interrupts TRX_IRQ_RX_START (shown in the use case below) or TRX_IRQ_AMI. When the MCU is ready to process more frames, the radio transceiver can be set back to one of the receive states RX_ON or RX_AACK_ON.

Code example

    /* AT86RF212::[RX_BUSY] */
    /* TRX_IRQ_RX_START occurs here */
    trx_bit_write(SR_TRX_CMD, CMD_PLL_ON);
    delay(tPSDU);
    /* AT86RF212::PLL_ON */
    frame = trx_frame_read();
    trx_bit_write(SR_TRX_CMD, CMD_RX_ON);
    trxstat = trx_bit_read(SR_TRX_STATUS);
    ASSERT(trxstat==RX_ON);
    /* AT86RF212::RX_ON */

SET_PROTECT_DYNAMIC

The dynamic frame buffer protection prevents the overwriting of valid frames until the frame read functions trx_frame_read() or by trx_frame_read_blm() have comleted.

A frame is classified as valid in the Basic Operating Mode (RX_ON) if it has a valid FCS. In the Extended Operating Mode (RX_AACK_ON) a frame is valid if it matches the address filter and has a valid FCS.

The protection is enabled by writing safe_mode=1 to SR_RX_SAFE_MODE and it holds until the end of a frame buffer read access, indicated by /SEL=HIGH.

Code example

    /* AT86RF212::[CONFIG] */
    trx_bit_write(SR_RX_SAFE_MODE, safe_mode);

GET_PROTECT_DYNAMIC

Reading the value safe_mode of SR_RX_SAFE_MODE indicates whether the dynamic frame protection is enabled or not.

Code example

    /* AT86RF212::[ACTIVE] */
    safe_mode = trx_bit_read(SR_RX_SAFE_MODE);