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| author | Miodrag Milanovic <mmicko@gmail.com> | 2024-11-29 09:04:06 +0100 |
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| committer | Miodrag Milanovic <mmicko@gmail.com> | 2024-11-29 09:04:06 +0100 |
| commit | 42be8d5bf0c2c6f3422b14cc4d264da7781da43b (patch) | |
| tree | a9692b6c12f964859df2143704750c9877bd33b6 /docs/format.html | |
| parent | 738af822905fdcf0466e9dd784b9ae4b0b34987f (diff) | |
Start converting documentation to Sphinx
Diffstat (limited to 'docs/format.html')
| -rw-r--r-- | docs/format.html | 170 |
1 files changed, 0 insertions, 170 deletions
diff --git a/docs/format.html b/docs/format.html deleted file mode 100644 index ee7a655..0000000 --- a/docs/format.html +++ /dev/null @@ -1,170 +0,0 @@ -<!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 – Bitstream File Format Documentation</title> -</head><body> -<h1>Project IceStorm – Bitstream File Format 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>General Description of the File Format</h2> - -<p> -The bitstream file starts with the bytes 0xFF 0x00, followed by a sequence of -zero-terminated comment strings, followed by 0x00 0xFF. However, there seems to be -a bug in the Lattice "bitstream" tool that moves the terminating 0x00 0xFF a few -bytes into the comment string in some cases. -</p> - -<p> -After the comment sections the token 0x7EAA997E (MSB first) starts the actual -bit stream. The bitstream consists of one-byte commands, followed by a payload -word, followed by an optional block of data. The MSB nibble of the command byte -is the command opcode, the LSB nibble is the length of the command payload in -bytes. The commands that do not require a payload are using the opcode 0, with -the command encoded in the payload field. Note that this "payload" in this -context refers to a single integer argument, not the blocks of data that -follows the command in case of the CRAM and BRAM commands. -</p> - -<p> -The following commands are known: -</p> - -<table class="ctab"> -<tr><th>Opcode</th><th>Description</th></tr> -<tr><td>0</td><td>payload=1: Write CRAM Data<br/> - payload=2: Read BRAM Data<br/> - payload=3: Write BRAM Data<br/> - payload=4: Read BRAM Data<br/> - payload=5: Reset CRC<br/> - payload=6: Wakeup<br/> - payload=8: Reboot</td></tr> -<tr><td>1</td><td>Set bank number</td></tr> -<tr><td>2</td><td>CRC check</td></tr> -<tr><td>4</td><td>Set boot address</td></tr> -<tr><td>5</td><td>Set internal oscillator frequency range<br/> - payload=0: low<br/> - payload=1: medium<br/> - payload=2: high</td></tr> -<tr><td>6</td><td>Set bank width (16-bits, MSB first)</td></tr> -<tr><td>7</td><td>Set bank height (16-bits, MSB first)</td></tr> -<tr><td>8</td><td>Set bank offset (16-bits, MSB first)</td></tr> -<tr><td>9</td><td>payload=0: Disable warm boot<br/> - payload=16: Enable cold boot<br/> - payload=32: Enable warm boot</td></tr> -</table> - -<p> -Use <span style="font-family:monospace">iceunpack -vv</span> to display the commands as they are interpreted by the tool. -</p> - -<p> -Note: The format itself seems to be very flexible. At the moment it is unclear what the FPGA -devices will do when presented with a bitstream that use the commands in a different way -than the bitstreams generated by the lattice tools. -</p> - -<h2>Writing SRAM content</h2> - -<p> -Most bytes in the bitstream are SRAM data bytes that should be written to the various SRAM banks -in the FPGA. The following sequence is used to program an SRAM cell: -</p> - -<ul> -<li>Set bank width (opcode 6)</li> -<li>Set bank height (opcode 7)</li> -<li>Set bank offset (opcode 8)</li> -<li>Set bank number (opcode 1)</li> -<li>CRAM or BRAM Data Command</li> -<li>(width * height / 8) data bytes</li> -<li>two zero bytes</li> -</ul> - -<p> -The bank width and height parameters reflect the width and height of the SRAM bank. A large SRAM can -be written in smaller chunks. In this case height parameter may be smaller and the offset parameter -reflects the vertical start position. -</p> - -<p> -There are four CRAM and four BRAM banks in an iCE40 FPGA. The different devices from the family -use different widths and heights, but the same number of banks. -</p> - -<p> -The CRAM banks hold the configuration bits for the FPGA fabric and hard IP blocks, the BRAM -corresponds to the contents of the block ram resources. -</p> - -<p> -The ordering of the data bits is in MSB first row-major order. -</p> - -<h2>Organization of the CRAM</h2> - -<p><a href="checkerboard.png"><img alt="Mapping of tile config bits to 2D CRAM" -style="float:right; padding:1em; padding-top:0; border:0" height="200" src="checkerboard.png"></a></p> - -<p> -The chip is organized into four quadrants. Each CRAM memory bank contains the configuration bits for one quadrant. -The address 0 is always the corner of the quadrant, i.e. in one quadrant the bit addresses increase with the tile x/y -coordinates, in another they increase with the tile x coordinate but decrease with the tile y coordinate, and so on. -</p> - -<p> -For an iCE40 1k device, that has 12 x 16 tiles (not counting the io tiles), the CRAM bank 0 is the one containing the corner tile (1 1), -the CRAM bank 1 contains the corner tile (1 16), the CRAM bank 2 contains the corner tile (12 1) and the CRAM bank 3 contains the -corner tile (12 16). The entire CRAM of such a device is depicted on the right (bank 0 is in the lower left corner in blue/green). -</p> - -<p> -The checkerboard pattern in the picture visualizes which bits are associated -with which tile. The height of the configuration block is 16 for all tile -types, but the width is different for each tile type. IO tiles have -configurations that are 18 bits wide, LOGIC tiles are 54 bits wide, and -RAM tiles are 42 bits wide. (Notice the two slightly smaller columns for the RAM tiles.) -</p> - -<p> -The IO tiles on the top and bottom of the chip use a strange permutation pattern for their bits. It can be seen in the picture that -their columns are spread out horizontally. What cannot be seen in the picture is the columns also are not in order and the bit -positions are vertically permuted as well. The <span style="font-family:monospace">CramIndexConverter</span> class in <span style="font-family:monospace">icepack.cc</span> encapsulates the calculations -that are necessary to convert between tile-relative bit addresses and CRAM bank-relative bit addresses. -</p> - -<p> -The black pixels in the image correspond to CRAM bits that are not associated with any IO, LOGIC or RAM tile. -Some of them are unused, others are used by hard IPs or other global resources. The <span style="font-family:monospace">iceunpack</span> tool reports -such bits, when set, with the "<span style="font-family:monospace">.extra_bit <i>bank x y</i></span>" statement in the ASCII output format. -</p> - -<h2>Organization of the BRAM</h2> - -<p> -This part of the documentation has not been written yet. -</p> - -<h2>CRC Check</h2> - -<p> -The CRC is a 16 bit CRC. The (truncated) polynomial is 0x1021 (CRC-16-CCITT). The "Reset CRC" command sets -the CRC to 0xFFFF. No zero padding is performed. -</p> - -</body></html> |