Chapter 41 gmac ethernet Interface

Power Management Block

Power management(PMT) supports the reception of network (remote) wake-up frames and Magic Packet frames. PMT does not perform the clock gate function, but generates interrupts for wake-up frames and Magic Packets received by the GMAC. The PMT block sits on the receiver path of the GMAC and is enabled with remote wake-up frame enable and Magic Packet enable. These enables are in the PMT control and status register and are programmed by the application.

When the power down mode is enabled in the PMT, then all received frames are dropped by the core and they are not forwarded to the application. The core comes out of the power down mode only when either a Magic Packet or a Remote Wake-up frame is received and the corresponding detection is enabled.

Remote Wake-Up Frame Detection

When the GMAC is in sleep mode and the remote wake-up bit is enabled in register GMAC_PMT_CTRL_STA (0x002C), normal operation is resumed after receiving a remote wake-up frame. The application writes all eight wake-up filter registers, by performing a sequential write to address (0028). The application enables remote wake-up by writing a 1 to bit 2 of the register GMAC_PMT_CTRL_STA.

Only
PMT supports four programmable filters that allow support of different receive frame patterns. If the incoming frame passes the address filtering of Filter Command, and if Filter CRC-16 matches the incoming examined pattern, then the wake-up frame is received.
Filter_offset (minimum value 12, which refers to the 13th byte of the frame) determines the offset from which the frame is to be examined. Filter Byte Mask determines which bytes of the frame must be examined. The thirty-first bit of Byte Mask must be set to zero.

T-chip
The remote wake-up CRC block determines the CRC value that is compared with Filter CRC-16. The wake-up frame is checked only for length error, FCS error, dribble bit error, GMII error, collision, and to ensure that it is not a runt frame. Even if the wake-up frame is more than 512 bytes long, if the frame has a valid CRC value, it is considered valid. Wake-up frame detection is updated in the register GMAC_PMT_CTRL_STA for every remote Wake-up frame received. A PMT interrupt to the application triggers a read to the GMAC_PMT_CTRL_STA register to determine reception of a wake-up frame.