UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
721 of 1269
NXP Semiconductors
UM10503
Chapter 26: LPC43xx Ethernet
26.7.1.4 System considerations during power-down
MAC neither gates nor stops clocks when Power-down mode is enabled. Power saving by
clock gating must be done outside the core by the application. The receive data path must
be clocked with ENET_RX_CLK during Power-down mode because it is involved in magic
packet/wake-on-LAN frame detection. However, the transmit path and the application path
clocks can be gated off during Power-down mode.
The PMT interrupt is asserted when a valid wake-up frame is received. This signal is
generated in the receive clock domain
The recommended power-down and wake-up sequence is as follows.
1. Disable the Transmit DMA and wait for any previous frame transmissions to complete.
These transmissions can be detected when Transmit Interrupt (see DMA_STAT
register bit NIS;
) is received.
2. Disable the MAC transmitter and MAC receiver by clearing the appropriate bits in the
MAC Configuration register.
3. Wait until the Receive DMA empties all the frames from the Rx FIFO (a software timer
may be required).
4. Enable Power-Down mode by appropriately configuring the PMT registers.
5. Enable the MAC Receiver and enter Power-Down mode.
6. Gate the application and transmit clock inputs to the core (and other relevant clocks in
the system) to reduce power and enter Sleep mode.
7. On receiving a valid wake-up frame, the MAC PMT interrupt signal and exits
Power-Down mode.
8. On receiving the interrupt, the system must enable the application and transmit clock
inputs to the core.
9. Read the PMT Status register to clear the interrupt, then enable the other modules in
the system and resume normal operation.
Remark:
26.7.2 DMA arbiter functions
If you have enabled the transmit (Tx) DMA and receive (Rx) DMA of a channel, you can
specify which DMA gets the bus when the channel gets the control of the bus. You can set
the priority between the corresponding Tx DMA and Rx DMA by using the bit 27 (TXPR:
Transmit Priority) of the DMA Bus Mode Register). For round-robin arbitration, you can
use the bits [15:14] (PR: Priority Ratio) of the Bus Mode Register to specify the weighted
priority between the Tx DMA and Rx DMA.
provides information about the
priority scheme between Tx DMA and Rx DMA.
Table 575. Priority scheme for transmit and receive DMA
Bit 27
Bit 15
Bit 14
Bit 1
Priority scheme
0
x
x
x
Rx always has priority over Tx
0
0
0
0
Tx and Rx have equal priority. Rx gets the access first on
simultaneous requests.
0
0
1
0
Rx has priority over Tx in the ratio 2:1.
0
1
0
0
Rx has priority over Tx in the ratio 3:1.