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| <title>Project IceStorm – LOGIC Tile Documentation</title> |
| </head><body> |
| <h1>Project IceStorm – LOGIC Tile Documentation</h1> |
| |
| <p> |
| <i><a href=".">Project IceStorm</a> aims at documenting the bitstream format of Lattice iCE40 |
| FPGAs and providing simple tools for analyzing and creating bitstream files. |
| This is work in progress.</i> |
| </p> |
| |
| <h2>Span-4 and Span-12 Wires</h2> |
| |
| <p> |
| The <i>span-4</i> and <i>span-12</i> wires are the main interconnect resource in iCE40 FPGAs. They "span" (have a length of) |
| 4 or 12 cells in horizontal or vertical direction. |
| </p> |
| |
| <p> |
| All routing resources in iCE40 are directional tristate buffers. The bits marked <span style="font-family:monospace">routing</span> |
| use the all-zeros config pattern for tristate, while the bits marked <span style="font-family:monospace">buffer</span> have |
| a dedicated buffer-enable bit, which is 1 in all non-tristate configurations. |
| </p> |
| |
| <h3 style="clear:both">Span-4 Horizontal</h3> |
| |
| <p><a href="sp4h.svg"><img alt="Span-4 Horizontal" style="float:right; padding:1em; padding-top:0; border:0" height="200" src="sp4h.svg"></a></p> |
| |
| <p> |
| The image on the right shows the <i>horizontal span-4</i> wires of a logic or ram cell (click to enlarge). |
| </p> |
| |
| <p> |
| On the left side of the cell there are 48 connections named <span style="font-family:monospace">sp4_h_l_0</span> to <span style="font-family:monospace">sp4_h_l_47</span>. The lower 36 of those |
| wires are connected to <span style="font-family:monospace">sp4_h_r_12</span> to <span style="font-family:monospace">sp4_h_r_47</span> on the right side of the cell. (IceStorm normalizes this |
| wire names to <span style="font-family:monospace">sp4_h_r_0</span> to <span style="font-family:monospace">sp4_h_r_35</span>. Note: the Lattice tools use a different normalization scheme |
| for this wire names.) The wires connecting the left and right horizontal span-4 ports are pairwise crossed-out. |
| </p> |
| |
| <p> |
| The wires <span style="font-family:monospace">sp4_h_l_36</span> to <span style="font-family:monospace">sp4_h_l_47</span> terminate in the cell as do the wires <span style="font-family:monospace">sp4_h_r_0</span> to <span style="font-family:monospace">sp4_h_r_11</span>. |
| </p> |
| |
| <p> |
| This wires "span" 4 cells, i.e. they connect 5 cells if you count the cells on |
| both ends of the wire. |
| </p> |
| |
| <p> |
| For example, the wire <span style="font-family:monospace">sp4_h_r_0</span> in cell (x, y) has the following names: |
| </p> |
| |
| <table class="ctab"> |
| <tr><th>Cell Coordinates</th><th>sp4_h_l_* wire name</th><th>sp4_h_r_* wire name</th></tr> |
| <tr><td>x, y</td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">sp4_h_r_0</span></td></tr> |
| <tr><td>x+1, y</td><td><span style="font-family:monospace">sp4_h_l_0</span></td><td><span style="font-family:monospace">sp4_h_r_13</span></td></tr> |
| <tr><td>x+2, y</td><td><span style="font-family:monospace">sp4_h_l_13</span></td><td><span style="font-family:monospace">sp4_h_r_24</span></td></tr> |
| <tr><td>x+3, y</td><td><span style="font-family:monospace">sp4_h_l_24</span></td><td><span style="font-family:monospace">sp4_h_r_37</span></td></tr> |
| <tr><td>x+4, y</td><td><span style="font-family:monospace">sp4_h_l_37</span></td><td><span style="font-family:monospace">-</span></td></tr> |
| </table> |
| |
| <h3 style="clear:both">Span-4 Vertical</h3> |
| |
| <p><a href="sp4v.svg"><img alt="Span-4 Vertical" style="float:right; padding:1em; padding-top:0; border:0" height="200" src="sp4v.svg"></a></p> |
| |
| <p> |
| The image on the right shows the <i>vertical span-4</i> wires of a logic or ram cell (click to enlarge). |
| </p> |
| |
| <p> |
| Similar to the horizontal span-4 wires there are 48 connections on the top (<span style="font-family:monospace">sp4_v_t_0</span> to <span style="font-family:monospace">sp4_v_t_47</span>) and |
| 48 connections on the bottom (<span style="font-family:monospace">sp4_v_b_0</span> to <span style="font-family:monospace">sp4_v_b_47</span>). The wires <span style="font-family:monospace">sp4_v_t_0</span> to <span style="font-family:monospace">sp4_v_t_35</span> |
| are connected to <span style="font-family:monospace">sp4_v_b_12</span> to <span style="font-family:monospace">sp4_v_b_47</span> (with pairwise crossing out). Wire names are normalized |
| to <span style="font-family:monospace">sp4_v_b_12</span> to <span style="font-family:monospace">sp4_v_b_47</span>. |
| </p> |
| |
| <p> |
| But in addition to that, each cell also has access to <span style="font-family:monospace">sp4_v_b_0</span> to <span style="font-family:monospace">sp4_v_b_47</span> of its right neighbour. |
| This are the wires <span style="font-family:monospace">sp4_r_v_b_0</span> to <span style="font-family:monospace">sp4_r_v_b_47</span>. So over all a single vertical span-4 wire |
| connects 9 cells. For example, the wire <span style="font-family:monospace">sp4_v_b_0</span> in cell (x, y) has the following names: |
| </p> |
| |
| <table class="ctab"> |
| <tr><th>Cell Coordinates</th><th>sp4_v_t_* wire name</th><th>sp4_v_b_* wire name</th><th>sp4_r_v_b_* wire name</th></tr> |
| <tr><td>x, y</td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">sp4_v_b_0</span></td><td><span style="font-family:monospace">-</span></td></tr> |
| <tr><td>x, y-1</td><td><span style="font-family:monospace">sp4_v_t_0</span></td><td><span style="font-family:monospace">sp4_v_b_13</span></td><td><span style="font-family:monospace">-</span></td></tr> |
| <tr><td>x, y-2</td><td><span style="font-family:monospace">sp4_v_t_13</span></td><td><span style="font-family:monospace">sp4_v_b_24</span></td><td><span style="font-family:monospace">-</span></td></tr> |
| <tr><td>x, y-3</td><td><span style="font-family:monospace">sp4_v_t_24</span></td><td><span style="font-family:monospace">sp4_v_b_37</span></td><td><span style="font-family:monospace">-</span></td></tr> |
| <tr><td>x, y-4</td><td><span style="font-family:monospace">sp4_v_t_37</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">-</span></td></tr> |
| <tr><td>x-1, y</td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">sp4_r_v_b_0</span></td></tr> |
| <tr><td>x-1, y-1</td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">sp4_r_v_b_13</span></td></tr> |
| <tr><td>x-1, y-2</td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">sp4_r_v_b_24</span></td></tr> |
| <tr><td>x-1, y-3</td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">sp4_r_v_b_37</span></td></tr> |
| </table> |
| |
| <h3 style="clear:both">Span-12 Horizontal and Vertical</h3> |
| |
| <p> |
| Similar to the span-4 wires there are also longer horizontal and vertical span-12 wires. |
| </p> |
| |
| <p> |
| There are 24 connections <span style="font-family:monospace">sp12_v_t_0</span> to <span style="font-family:monospace">sp12_v_t_23</span> on the top of the |
| cell and 24 connections <span style="font-family:monospace">sp12_v_b_0</span> to <span style="font-family:monospace">sp12_v_b_23</span> on the bottom of the |
| cell. The wires <span style="font-family:monospace">sp12_v_t_0</span> to <span style="font-family:monospace">sp12_v_t_21</span> are connected to |
| <span style="font-family:monospace">sp12_v_b_2</span> to <span style="font-family:monospace">sp12_v_b_23</span> (with pairwise crossing out). The connections |
| <span style="font-family:monospace">sp12_v_b_0</span>, <span style="font-family:monospace">sp12_v_b_1</span>, <span style="font-family:monospace">sp12_v_t_22</span>, and <span style="font-family:monospace">sp12_v_t_23</span> |
| terminate in the cell. Wire names are normalized to <span style="font-family:monospace">sp12_v_b_2</span> to <span style="font-family:monospace">sp12_v_b_23</span>. |
| </p> |
| |
| <p> |
| There are also 24 connections <span style="font-family:monospace">sp12_h_l_0</span> to <span style="font-family:monospace">sp12_h_l_23</span> on the left of the |
| cell and 24 connections <span style="font-family:monospace">sp12_h_r_0</span> to <span style="font-family:monospace">sp12_h_r_23</span> on the right of the |
| cell. The wires <span style="font-family:monospace">sp12_h_l_0</span> to <span style="font-family:monospace">sp12_h_l_21</span> are connected to |
| <span style="font-family:monospace">sp12_h_r_2</span> to <span style="font-family:monospace">sp12_h_r_23</span> (with pairwise crossing out). The connections |
| <span style="font-family:monospace">sp12_h_r_0</span>, <span style="font-family:monospace">sp12_h_r_1</span>, <span style="font-family:monospace">sp12_h_l_22</span>, and <span style="font-family:monospace">sp12_h_l_23</span> |
| terminate in the cell. Wire names are normalized to <span style="font-family:monospace">sp12_v_r_2</span> to <span style="font-family:monospace">sp12_h_r_23</span>. |
| </p> |
| |
| <h2>Local Tracks</h2> |
| |
| <p> |
| The <i>local tracks</i> are the gateway to the logic cell inputs. Signals from the span-wires |
| and the logic cell outputs of the eight neighbour cells can be routed to the local tracks and |
| signals from the local tracks can be routed to the logic cell inputs. |
| </p> |
| |
| <p> |
| Each logic tile has 32 local tracks. They are organized in 4 groups of 8 wires each: |
| <span style="font-family:monospace">local_g0_0</span> to <span style="font-family:monospace">local_g3_7</span>. |
| </p> |
| |
| <p> |
| The span wires, global signals, and neighbour outputs can be routed to the local tracks. But not |
| all of those signals can be routed to all of the local tracks. Instead there is a different |
| mix of 16 signals for each local track. |
| </p> |
| |
| <p> |
| The buffer driving the local track has 5 configuration bits. One enable bit and 4 bits that select |
| the input wire. For example for <span style="font-family:monospace">local_g0_0</span> (copy&paste from the bitstream doku): |
| </p> |
| |
| <table class="ctab"> |
| <tr><th style="width:5em">B0[14]</th><th style="width:5em">B1[14]</th><th style="width:5em">B1[15]</th><th style="width:5em">B1[16]</th> <th style="width:5em">B1[17]</th> |
| <th style="width:5em">Function</th><th style="width:15em">Source-Net</th><th style="width:15em">Destination-Net</th></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_r_v_b_24</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp12_h_r_8</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">neigh_op_bot_0</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_v_b_16</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_r_v_b_35</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp12_h_r_16</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">neigh_op_top_0</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_h_r_0</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">lutff_0/out</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_v_b_0</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">neigh_op_lft_0</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_h_r_8</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">neigh_op_bnr_0</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_v_b_8</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp12_h_r_0</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">sp4_h_r_16</span></td><td><span style="font-family:monospace">local_g0_0</span></td></tr> |
| </table> |
| |
| <p> |
| Then the signals on the local tracks can be routed to the input pins of the logic cells. Like before, |
| not every local track can be routed to every logic cell input pin. Instead there is a different mix |
| of 16 local track for each logic cell input. For example for <span style="font-family:monospace">lutff_0/in_0</span>: |
| </p> |
| |
| <table class="ctab"> |
| <tr><th style="width:5em">B0[26]</th><th style="width:5em">B1[26]</th><th style="width:5em">B1[27]</th><th style="width:5em">B1[28]</th><th style="width:5em">B1[29]</th> |
| <th style="width:5em">Function</th><th style="width:15em">Source-Net</th><th style="width:15em">Destination-Net</th></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g0_0</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g2_0</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g1_1</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g3_1</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g0_2</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g2_2</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g1_3</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g3_3</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g0_4</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g2_4</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g1_5</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g3_5</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g0_6</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g2_6</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g1_7</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">buffer</td><td><span style="font-family:monospace">local_g3_7</span></td><td><span style="font-family:monospace">lutff_0/in_0</span></td></tr> |
| </table> |
| |
| <p> |
| The 8 global nets on the iCE40 can be routed to the local track via the <span style="font-family:monospace">glb2local_0</span> to <span style="font-family:monospace">glb2local_3</span> |
| nets using a similar two-stage process. The logic block clock-enable and set-reset inputs can be driven |
| directly from one of 4 global nets or from one of 4 local tracks. The logic block clock input can be driven |
| from any of the global nets and from a few local tracks. See the bitstream documentation for details. |
| </p> |
| |
| <h2>Logic Block</h2> |
| |
| <p> |
| Each logic tile has a logic block containing 8 logic cells. Each logic cell contains a 4-input LUT, a carry |
| unit and a flip-flop. Clock, clock enable, and set/reset inputs are shared along the 8 logic cells. So is the |
| bit that configures positive/negative edge for the flip flops. But the three configuration bits that specify if |
| the flip flop should be used, if it is set or reset by the set/reset input, and if the set/reset is synchronous |
| or asynchronous exist for each logic cell individually. |
| </p> |
| |
| <p> |
| Each LUT <i>i</i> has four input wires <span style="font-family:monospace">lutff_<i>i</i>/in_0</span> to <span style="font-family:monospace">lutff_<i>i</i>/in_3</span>. Input |
| <span style="font-family:monospace">lutff_<i>i</i>/in_3</span> can be configured to be driven by the carry output of the previous logic cell, |
| or by <span style="font-family:monospace">carry_in_mux</span> in case of <i>i</i>=0. Input <span style="font-family:monospace">lutff_<i>i</i>/in_2</span> can be configured to |
| be driven by the output of the previous LUT for <i>i</i>>0 (LUT cascade). The LUT uses its 4 input signals to |
| calculate <span style="font-family:monospace">lutff_<i>i</i>/lout</span>. The signal is then passed through the built-in FF |
| and becomes <span style="font-family:monospace">lutff_<i>i</i>/out</span>. With the exception of LUT cascades, only the signal |
| after the FF is visible from outside the logic block. |
| </p> |
| |
| <p> |
| The carry unit calculates <span style="font-family:monospace">lutff_<i>i</i>/cout</span> = <span style="font-family:monospace">lutff_<i>i</i>/in_1</span> + <span style="font-family:monospace">lutff_<i>i</i>/in_2</span> + <span style="font-family:monospace">lutff_<i>(i-1)</i>/cout</span> > 1. In case of <i>i</i>=0, <span style="font-family:monospace">carry_in_mux</span> is used as third input. <span style="font-family:monospace">carry_in_mux</span> can be configured to be constant 0, 1 or the <span style="font-family:monospace">lutff_7/cout</span> signal from the logic tile below. |
| </p> |
| |
| <p> |
| Part of the functionality described above is documented as part of the routing |
| bitstream documentation (see the buffers for <span style="font-family:monospace">lutff_</span> inputs). The <span style="font-family:monospace">NegClk</span> |
| bit switches all 8 FFs in the tile to negative edge mode. The <span style="font-family:monospace">CarryInSet</span> |
| bit drives the <span style="font-family:monospace">carry_in_mux</span> high (it defaults to low when not driven via the buffer from |
| <span style="font-family:monospace">carry_in</span>). |
| </p> |
| |
| <p> |
| The remaining functions of the logic cell are configured via the <span style="font-family:monospace">LC_<i>i</i></span> bits. This |
| are 20 bit per logic cell. We have arbitrarily labeled those bits as follows: |
| </p> |
| |
| <table class="ctab"> |
| <tr><th>Label</th><th>LC_0</th><th>LC_1</th><th>LC_2</th><th>LC_3</th><th>LC_4</th><th>LC_5</th><th>LC_6</th><th>LC_7</th></tr> |
| <tr><td>LC_<i>i</i>[0]</td><td>B0[36]</td><td>B2[36]</td><td>B4[36]</td><td>B6[36]</td><td>B8[36]</td><td>B10[36]</td><td>B12[36]</td><td>B14[36]</td></tr> |
| <tr><td>LC_<i>i</i>[1]</td><td>B0[37]</td><td>B2[37]</td><td>B4[37]</td><td>B6[37]</td><td>B8[37]</td><td>B10[37]</td><td>B12[37]</td><td>B14[37]</td></tr> |
| <tr><td>LC_<i>i</i>[2]</td><td>B0[38]</td><td>B2[38]</td><td>B4[38]</td><td>B6[38]</td><td>B8[38]</td><td>B10[38]</td><td>B12[38]</td><td>B14[38]</td></tr> |
| <tr><td>LC_<i>i</i>[3]</td><td>B0[39]</td><td>B2[39]</td><td>B4[39]</td><td>B6[39]</td><td>B8[39]</td><td>B10[39]</td><td>B12[39]</td><td>B14[39]</td></tr> |
| <tr><td>LC_<i>i</i>[4]</td><td>B0[40]</td><td>B2[40]</td><td>B4[40]</td><td>B6[40]</td><td>B8[40]</td><td>B10[40]</td><td>B12[40]</td><td>B14[40]</td></tr> |
| <tr><td>LC_<i>i</i>[5]</td><td>B0[41]</td><td>B2[41]</td><td>B4[41]</td><td>B6[41]</td><td>B8[41]</td><td>B10[41]</td><td>B12[41]</td><td>B14[41]</td></tr> |
| <tr><td>LC_<i>i</i>[6]</td><td>B0[42]</td><td>B2[42]</td><td>B4[42]</td><td>B6[42]</td><td>B8[42]</td><td>B10[42]</td><td>B12[42]</td><td>B14[42]</td></tr> |
| <tr><td>LC_<i>i</i>[7]</td><td>B0[43]</td><td>B2[43]</td><td>B4[43]</td><td>B6[43]</td><td>B8[43]</td><td>B10[43]</td><td>B12[43]</td><td>B14[43]</td></tr> |
| <tr><td>LC_<i>i</i>[8]</td><td>B0[44]</td><td>B2[44]</td><td>B4[44]</td><td>B6[44]</td><td>B8[44]</td><td>B10[44]</td><td>B12[44]</td><td>B14[44]</td></tr> |
| <tr><td>LC_<i>i</i>[9]</td><td>B0[45]</td><td>B2[45]</td><td>B4[45]</td><td>B6[45]</td><td>B8[45]</td><td>B10[45]</td><td>B12[45]</td><td>B14[45]</td></tr> |
| <tr><td>LC_<i>i</i>[10]</td><td>B1[36]</td><td>B3[36]</td><td>B5[36]</td><td>B7[36]</td><td>B9[36]</td><td>B11[36]</td><td>B13[36]</td><td>B15[36]</td></tr> |
| <tr><td>LC_<i>i</i>[11]</td><td>B1[37]</td><td>B3[37]</td><td>B5[37]</td><td>B7[37]</td><td>B9[37]</td><td>B11[37]</td><td>B13[37]</td><td>B15[37]</td></tr> |
| <tr><td>LC_<i>i</i>[12]</td><td>B1[38]</td><td>B3[38]</td><td>B5[38]</td><td>B7[38]</td><td>B9[38]</td><td>B11[38]</td><td>B13[38]</td><td>B15[38]</td></tr> |
| <tr><td>LC_<i>i</i>[13]</td><td>B1[39]</td><td>B3[39]</td><td>B5[39]</td><td>B7[39]</td><td>B9[39]</td><td>B11[39]</td><td>B13[39]</td><td>B15[39]</td></tr> |
| <tr><td>LC_<i>i</i>[14]</td><td>B1[40]</td><td>B3[40]</td><td>B5[40]</td><td>B7[40]</td><td>B9[40]</td><td>B11[40]</td><td>B13[40]</td><td>B15[40]</td></tr> |
| <tr><td>LC_<i>i</i>[15]</td><td>B1[41]</td><td>B3[41]</td><td>B5[41]</td><td>B7[41]</td><td>B9[41]</td><td>B11[41]</td><td>B13[41]</td><td>B15[41]</td></tr> |
| <tr><td>LC_<i>i</i>[16]</td><td>B1[42]</td><td>B3[42]</td><td>B5[42]</td><td>B7[42]</td><td>B9[42]</td><td>B11[42]</td><td>B13[42]</td><td>B15[42]</td></tr> |
| <tr><td>LC_<i>i</i>[17]</td><td>B1[43]</td><td>B3[43]</td><td>B5[43]</td><td>B7[43]</td><td>B9[43]</td><td>B11[43]</td><td>B13[43]</td><td>B15[43]</td></tr> |
| <tr><td>LC_<i>i</i>[18]</td><td>B1[44]</td><td>B3[44]</td><td>B5[44]</td><td>B7[44]</td><td>B9[44]</td><td>B11[44]</td><td>B13[44]</td><td>B15[44]</td></tr> |
| <tr><td>LC_<i>i</i>[19]</td><td>B1[45]</td><td>B3[45]</td><td>B5[45]</td><td>B7[45]</td><td>B9[45]</td><td>B11[45]</td><td>B13[45]</td><td>B15[45]</td></tr> |
| </table> |
| |
| <p> |
| <span style="font-family:monospace">LC_<i>i</i>[8]</span> is the <span style="font-family:monospace">CarryEnable</span> bit. This bit must be set if the carry logic is used. |
| </p> |
| |
| <p> |
| <span style="font-family:monospace">LC_<i>i</i>[9]</span> is the <span style="font-family:monospace">DffEnable</span> bit. It enables the output flip-flop for the LUT. |
| </p> |
| |
| <p> |
| <span style="font-family:monospace">LC_<i>i</i>[18]</span> is the <span style="font-family:monospace">Set_NoReset</span> bit. When this bit is set then the set/reset signal will set, not reset the flip-flop. |
| </p> |
| |
| <p> |
| <span style="font-family:monospace">LC_<i>i</i>[19]</span> is the <span style="font-family:monospace">AsyncSetReset</span> bit. When this bit is set then the set/reset signal is asynchronous to the clock. |
| </p> |
| |
| <p> |
| The LUT implements the following truth table: |
| </p> |
| |
| <table class="ctab"> |
| <tr><th>in_3</th><th>in_2</th><th>in_1</th><th>in_0</th><th>lout</th></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[4]</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[14]</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[15]</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[5]</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[6]</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[16]</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[17]</span></td></tr> |
| <tr><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[7]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[3]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[13]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[12]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[2]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[1]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[11]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">0</td><td><span style="font-family:monospace">LC_<i>i</i>[10]</span></td></tr> |
| <tr><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td style="text-align:center">1</td><td><span style="font-family:monospace">LC_<i>i</i>[0]</span></td></tr> |
| </table> |
| |
| <p> |
| LUT inputs that are not connected to anything are driven low. The set/reset |
| signal is also driven low if not connected to any other driver, and the clock |
| enable signal is driven high when left unconnected. |
| </p> |
| |
| </body></html> |
