3.1.11. Low Power Mode (LPM)
Enabling and Disabling Low Power Mode
Use registers 0x200-0x203 to enable LPM. LPM is enabled one channel at a time. Use the base address for the desired channel when doing the register writes to enable LPM for that calling channel. For example, to load to channel 0:
- Write 0x01 to 0x200 to enable LPM, or write 0x00 to 0x200 to disable LPM.
- Write 0x00 to 0x201 as this should be all 0’s.
- Write 0x00 to 0x202 to target the calling channel (channel 0 in this case).
- Write 0x98 to 0x203 to use the OPCODE for LOW_POWER_MODE. See the "Loading PMA Configuration Register LOW_POWER_MODE" figure for details.
While in Low Power Mode
- LPM determines the mode of the implementation and turns off unused IP and DFT.
- Initial adaptation and continuous adaptation function normally.
- Adaptive settings perform normally.
- Mission mode performance is unaffected.
- There are no timing constraints or requirements.
- There are no issues with changing PMA static settings.
When to Enable or Disable Low Power Mode
- Disable LPM before changing the functional mode (from NRZ to PAM4 or from PAM4 to NRZ). Re-enable LPM after the change.
- Enabling and disabling LPM does not impact performance.
- Disable LPM before disabling the transceiver. If you do not, you must perform a PMA analog reset to recover the transceiver.
- A PMA analog reset exits LPM, so re-enable LPM after performing adaptation that requires a PMA analog reset.
- Intel recommends disabling LPM for DFT functions such as internal serial loopback, reverse parallel loopback, and eye measurements.
- However, when DFT is utilized in LPM, the associated IP is turned on. To regain the best power performance, re-enable LPM.
How to Use Internal Serial Loopback
Internal serial loopback mode does not work in conjunction with LPM because the phase interpolator is disabled and there is no activity in the receiver. To use internal serial loopback mode:
- Disable LPM.
- Enable internal serial loopback mode.
- Perform testing.
- Disable internal serial loopback mode to enter mission mode.
- Re-enable LPM.
Unused Transceiver Channel Implementation with Low Power Mode
- Configure unused transceiver channels in internal serial or reverse parallel loopback mode. See Unused Transceiver Channels for details.
- Enter LPM. See "Enabling and Disabling Low Power Mode" above and the "Loading PMA Configuration Register LOW_POWER_MODE" figure for details.
- Enable PLL (this can be part of the LPM register writes). See the "Loading PMA Configuration Register LOW_POWER_MODE" figure for details. Or use PMA attribute 0x8092 0x188C.
RX and TX toggle as normal, but the data may have errors.
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