CoreU1PHY – UTOPIA Level 1 PHY Interface

v4.0

3

Alternatively, the link-layer device may choose to stall in-

between cells without deselecting the physical interface,

as illustrated in Figure 4.

If the link-layer has another cell to send to the physical

interface and if polling during the current cell indicates

that the CoreU1PHY is able to accept another cell, the

link-layer may send cells back-to-back, as illustrated in

Figure 5.

RX Interface (Egress)

The RX interface operates in a similar manner. The

process begins with u1_rx_clav. If the user interface

indicates there is at least one complete cell available for

transfer by asserting r_avail high, the core responds with

u1_rx_clav high; otherwise, u1_rx_clav is asserted low

and the link-layer device must wait until the user logic

indicates that a cell is available for transfer.

To begin receiving cells on the RX interface, the link-

layer must select the CoreU1PHY by asserting u1_rx_en

low (Figure 6).

The

CoreU1PHY

will

then

assert

u1_rx_soc

high,

indicating that the first word of the cell transfer is active

on the bus. Once a transfer has begun, all 53 or 54 bytes

of the cell are transferred without interruption.

If polling during the current transfer indicates that there

are no more cells available, or if the link-layer is unable

to receive another cell from the CoreU1PHY, the link-

layer may deselect the physical interface by de-asserting

u1_rx_en after receiving the last byte of the current cell,

as illustrated in Figure 7.

If the link-layer continues to enable the CoreU1PHY

during the last two bytes of the current cell transfer, and

one or more complete ATM cells are ready to be

transferred (u1_rx_avail is high), the CoreU1PHY will

send back-to-back cells, as shown in Figure 8. If the user

interface indicates r_avail low (no data to send), but the

link-layer

continues

to

assert

U1_rx_en

low,

the

CoreU1PHY interface will remain idle until r_avail is

asserted high on the user interface and another cell

transfer begins.

Figure 4 • TX Stalled by u1_tx_clav

Figure 5 • TX Back-to-Back Transfer

Figure 6 • RX Start of Cell Transfer

P51 P52 P53 P54

XX

H1

H2

u1_tx_clk

u1_tx_clav

u1_tx_en

u1_tx_soc

u1_tx_data

u1_tx_clk

u1_tx_clav

u1_tx_en

u1_tx_soc

u1_tx_data

P51 P52 P53 P54 H1 H2

H3 H4 H5 H6

H1 H2

u1_rx_clk

u1_rx_clav

u1_rx_en

u1_rx_soc

u1_rx_data

Figure 7 • RX End of Transfer

Figure 8 • RX Back-to-Back Transfer

P51

P52

P53

P54

XX

u1_rx_clk

u1_rx_clav

u1_rx_en

u1_rx_soc

u1_rx_data

P51 P52 P53 P54 H1 H2 H3 H4 H5

u1_rx_clk

u1_rx_clav

u1_rx_en

u1_rx_soc

u1_rx_data