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authorMiodrag Milanovic <mmicko@gmail.com>2024-11-29 09:04:06 +0100
committerMiodrag Milanovic <mmicko@gmail.com>2024-11-29 09:04:06 +0100
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-<!DOCTYPE html>
-<html><head><meta charset="UTF-8">
-<style>
-.ctab {
- margin-left: auto;
- margin-right: auto;
- border: 1px solid gray;
-}
-.ctab td, .ctab th {
- padding: 3px;
- border: 1px solid gray;
-}
-</style>
-<title>Project IceStorm &ndash; RAM Tile Documentation</title>
-</head><body>
-<h1>Project IceStorm &ndash; RAM 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>
-Regarding the Span-4 and Span-12 Wires a RAM tile behaves exactly like a LOGIC tile. So for simple
-applications that do not need the block ram resources, the RAM tiles can be handled like a LOGIC
-tiles without logic cells in them.
-</p>
-
-<h2>Block RAM Resources</h2>
-
-<p>
-A pair or RAM tiles (odd and even y-coordinates) provides an interface to a block ram cell. Like with
-LOGIC tiles, signals entering the RAM tile have to be routed over local tracks to the block ram
-inputs. Tiles with odd y-coordinates are "bottom" RAM Tiles (RAMB Tiles), and tiles with even y-coordinates
-are "top" RAM Tiles (RAMT Tiles). Each pair of RAMB/RAMT tiles implements a <span style="font-family:monospace">SB_RAM40_4K</span> cell. The
-cell ports are spread out over the two tiles as follows:
-</p>
-
-<table class="ctab">
-<tr><th>SB_RAM40_4K</th><th>RAMB Tile</th><th>RAMT Tile</th></tr>
-<tr><td><span style="font-family:monospace">RDATA[15:0]</span></td><td><span style="font-family:monospace">RDATA[7:0]</span></td><td><span style="font-family:monospace">RDATA[15:8]</span></td></tr>
-<tr><td><span style="font-family:monospace">RADDR[10:0]</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">RADDR[10:0]</span></td></tr>
-<tr><td><span style="font-family:monospace">WADDR[10:0]</span></td><td><span style="font-family:monospace">WADDR[10:0]</span></td><td><span style="font-family:monospace">-</span></td></tr>
-<tr><td><span style="font-family:monospace">MASK[15:0]</span></td><td><span style="font-family:monospace">MASK[7:0]</span></td><td><span style="font-family:monospace">MASK[15:8]</span></td></tr>
-<tr><td><span style="font-family:monospace">WDATA[15:0]</span></td><td><span style="font-family:monospace">WDATA[7:0]</span></td><td><span style="font-family:monospace">WDATA[15:8]</span></td></tr>
-<tr><td><span style="font-family:monospace">RCLKE</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">RCLKE</span></td></tr>
-<tr><td><span style="font-family:monospace">RCLK</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">RCLK</span></td></tr>
-<tr><td><span style="font-family:monospace">RE</span></td><td><span style="font-family:monospace">-</span></td><td><span style="font-family:monospace">RE</span></td></tr>
-<tr><td><span style="font-family:monospace">WCLKE</span></td><td><span style="font-family:monospace">WCLKE</span></td><td><span style="font-family:monospace">-</span></td></tr>
-<tr><td><span style="font-family:monospace">WCLK</span></td><td><span style="font-family:monospace">WCLK</span></td><td><span style="font-family:monospace">-</span></td></tr>
-<tr><td><span style="font-family:monospace">WE</span></td><td><span style="font-family:monospace">WE</span></td><td><span style="font-family:monospace">-</span></td></tr>
-</table>
-
-<p>
-The configuration bit <span style="font-family:monospace">RamConfig PowerUp</span> in the RAMB tile enables the memory. This bit
-is active-low in 1k chips, i.e. an unused RAM block has only this bit set. Note that <span style="font-family:monospace">icebox_explain.py</span>
-will ignore all RAMB tiles that only have the <span style="font-family:monospace">RamConfig PowerUp</span> bit set.
-</p>
-
-<p>
-In 8k chips the <span style="font-family:monospace">RamConfig PowerUp</span> bit is active-high. So an unused RAM block has all bits cleared
-in the 8k config bitstream.
-</p>
-
-<p>
-The <span style="font-family:monospace">RamConfig CBIT_*</span> bits in the RAMT tile configure the read/write width of the
-memory. Those bits map to the <span style="font-family:monospace">SB_RAM40_4K</span> cell parameters as follows:
-</p>
-
-<table class="ctab">
-<tr><th>SB_RAM40_4K</th><th>RAMT Config Bit</th></tr>
-<tr><td><span style="font-family:monospace">WRITE_MODE[0]</span></td><td><span style="font-family:monospace">RamConfig CBIT_0</span></td></tr>
-<tr><td><span style="font-family:monospace">WRITE_MODE[1]</span></td><td><span style="font-family:monospace">RamConfig CBIT_1</span></td></tr>
-<tr><td><span style="font-family:monospace">READ_MODE[0]</span></td><td><span style="font-family:monospace">RamConfig CBIT_2</span></td></tr>
-<tr><td><span style="font-family:monospace">READ_MODE[1]</span></td><td><span style="font-family:monospace">RamConfig CBIT_3</span></td></tr>
-</table>
-
-<p>
-The read/write mode selects the width of the read/write port:
-</p>
-
-<table class="ctab">
-<tr><th>MODE</th><th>DATA Width</th><th>Used WDATA/RDATA Bits</th></tr>
-<tr><td>0</td><td>16</td><td>15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0</td></tr>
-<tr><td>1</td><td>8</td><td>14, 12, 10, 8, 6, 4, 2, 0</td></tr>
-<tr><td>2</td><td>4</td><td>13, 9, 5, 1</td></tr>
-<tr><td>3</td><td>2</td><td>11, 3</td></tr>
-</table>
-
-<p>
-The <span style="font-family:monospace">NegClk</span> bit in the RAMB tile (1k die) or RAMT tile (other devices) negates the polarity of the <span style="font-family:monospace">WCLK</span> port,
-and the <span style="font-family:monospace">NegClk</span> bit in the RAMT (1k die) or RAMB tile (other devices) tile negates the polarity of the <span style="font-family:monospace">RCLK</span> port.
-</p>
-
-<p>
-A logic tile sends the output of its eight logic cells to its neighbour tiles. A RAM tile does the same thing
-with the <span style="font-family:monospace">RDATA</span> outputs. Each RAMB tile exports its <span style="font-family:monospace">RDATA[7:0]</span> outputs and each RAMT tile
-exports its <span style="font-family:monospace">RDATA[15:8]</span> outputs via this mechanism.
-</p>
-
-</body></html>
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