arm-netbook

arm-netbook@lists.phcomp.co.uk

1082 discussions

HDMI High-Frequency Layout: Libre Field Solvers
by Richard Wilbur 04 Aug '17

04 Aug '17

HDMI Layout Notes for EOMA68 Cards by Richard Wilbur Libre Field Solvers[24] (Free Computational Electromagnetic Modeling Codes list at the Clemson University Vehicular Electronics Laboratory) Name License URL Angora GPL http://www.angorafdtd.org/ atlc - Arbitrary Transmission Line Calculator (for transmission lines and directional couplers) GPL http://atlc.sourceforge.net/ Elmer GPL/LGPL https://www.csc.fi/web/elmer EMAP BSD-esque? http://www.cvel.clemson.edu/modeling/EMAG/EMAP/emap5/ FastImp MIT http://www.rle.mit.edu/cpg/fastimp.htm GSVIT GPL http://gsvit.net/ MEEP GPL http://ab-initio.mit.edu/wiki/index.php/Meep MMTL - Multilayer Multiconductor Transmission Line GPL http://mmtl.sourceforge.net/ openEMS GPLv3+ http://openems.de/start/index.php OpenMaXwell GPLv3+ http://openmax.ethz.ch/ (runs on Linux under wine) pdnMesh GPLv2 http://pdnmesh.sourceforge.net/ Puma-EM GPLv2 https://sourceforge.net/projects/puma-em/ WOLFSIM GPLv2 https://sourceforge.net/projects/wolfsim/ xfemm - Cross-platform Finite Element Method Magnetics Aladdin Free Public License, Apache Licence v2.0 https://sourceforge.net/projects/xfemm/ These are the field solvers that had what I understood to be a libre license from Clemson's list. There are fourteen packages here that made the cut and align with the goals of this project. I have no familiarity nor expertise with any of them or I would be in a better position to make a recommendation. It would be useful to be able to model not only the differential microstrip structure with ground shield traces and vias, but also signal vias for tuning them to transparency. References: [24] http://www.cvel.clemson.edu/modeling/EMAG/free-codes.html

1 0

HDMI High-Frequency Layout: Goals
by Richard Wilbur 03 Aug '17

03 Aug '17

HDMI Layout Notes for EOMA68 Cards by Richard Wilbur Goals The portion of the HDMI transmission path contained on the PCB has several goals: 1. Support all operating modes of the HDMI v1.4 interface of which the A20 chip is capable (clock up to 340MHz, data up to 3.4GHz). 2. Match the characteristic impedance of the rest of the HDMI transmission path (connectors, cable, and receiver) to minimize reflections and deliver a recoverable/decodeable signal to the receiver. [low distortion, sufficient amplitude] 3. Minimize radiated Electro-Magnetic Interference which could adversely effect other circuits on the EOMA68-A20 or in its surroundings, or exceed regulatory limits of concerned agencies: FCC, CSA, etc. 4. Minimize sensitivity to EMI from other circuits on the EOMA68-A20 and its surroundings. Of these goals careful layout realizing a microstrip geometry helps with minimizing EMI radiation and sensitivity, while impedance matching both minimizes signal reflections which distort the transmitted signal and delivers the signal energy to the intended receiver.

1 0

Re: [Arm-netbook] HDMI High-Frequency Layout: Introduction
by Andrew Bolin 02 Aug '17

02 Aug '17

> > Date: Tue, 1 Aug 2017 03:45:19 -0600 > From: Richard Wilbur <richard.wilbur(a)gmail.com> > To: Eco-Conscious <arm-netbook(a)lists.phcomp.co.uk> > Subject: [Arm-netbook] HDMI High-Frequency Layout: Introduction > Message-ID: > <CAC4=CAENg63=p1CfYFE6QPVp+g1-SRnznHbXTsVcNkLXh=EY9A@mail. > gmail.com> > Content-Type: text/plain; charset="UTF-8" > > This is a discussion of the considerations when designing and > executing a PCB layout containing high-frequency signal > traces--specifically in this case HDMI. It is being published to the > [arm-netbook] mailing list in several sections dealing with related > topics. The original was created in Open Document Text and I have > dumped it into Unicode Text in order to accommodate the mailing list. > Great collection of info Richard. I'd appreciate a copy of the original file to keep for my reference, if/when you have a chance to upload it somewhere (I'm guessing I'm not the only one?), or email it direct and I can find a place to share it.

3 2

HDMI High-Frequency Layout: Timing
by Richard Wilbur 01 Aug '17

01 Aug '17

HDMI Layout Notes for EOMA68 Cards by Richard Wilbur Timing Now that we have a speed of propagation, let's figure out the timing constraints imposed by the HDMI standard to the level we plan to support--v1.4. The standard doesn't seem to be freely available so, thankfully, several manufacturers mention various timing constraints in their documentation. The maximum pixel clock frequency is revealed in Toradex' design guide. Max Frequency: (HDMI v1.0-1.2a) 825 MHz (165 MHz pixel clock) (HDMI v1.3-1.4) 1.65 GHz (340 MHz pixel clock)[3] For a transmitter, many impedance improprieties (mismatches) can be forgiven in the first quarter-wavelength of propagation. T(Pixel) = 1/(pixel clock) = 1/(340MHz) = 2.94ns wavelength = velocity * period = 150um/ps * 2940ps = 441mm = 17400mil quarter wavelength = wavelength / 4 = 4350mil So, while we will try to match the impedance of our traces (transmission lines) as carefully as possible to the characteristic impedance specified for the cable, until we get to 4.3 inches from the signal source the line driver should be able to squash most reflections on the leading edges (first quarter wavelength). Impedance still matters for proper signal levels, but more in the bulk sense. The problem we will first turn our attention to, then, is that of skew (differences in signal arrival time) usually most noticeably caused by differences in trace length. Several goals are outlined in the literature I reviewed: skew between the clock pair and any data pair, skew between any two pairs (both of these fall under what I would call "Inter-pair Skew"), and skew between the traces of a particular pair ("Intra-pair Skew"). Inter-pair skew: (Requirements for HDMI v1.4) clock-data skew: Δt <150ps[3] => Δl < v * Δt = 22mm ~= 870mil T(Pixel) = 1/(pixel clock) = 2.94ns Skew(Inter-Pair) < 0.20 * T(Pixel)[4][5] = 588ps => Δl < v * Δt = 88.2mm ~= 3470mil Chrontel suggests matching between any two pairs be within 100mil.[5] => Δl < 100mil => Δt < Δl / v = 2540um / (150um/ps) = 17ps Of these design parameters Chrontel's 100mil recommendation seems to be the most restrictive, but still not out of the realm of possibility and probably a good precautionary limit. With only 17ps of inter-pair skew we meet even much tighter skew timings. Having non-vanishing inter-pair skew seems to actually be beneficial for reducing Electro-Magnetic Interference (EMI) by avoiding simultaneous transitions on multiple lines. Indeed the standard seems to be designed to recover up to 5 bits of worst-case inter-pair skew.[6] (Half of the 10-bit pixel time.) A Texas Instruments (TI) employee specifically suggested to keep the clock pair longer than the data pairs.[7] Intra-pair skew: (Requirements for HDMI v1.4) Toradex: Δt < 5ps[3] => Δl < v * Δt = 0.75mm ~= 30 mil Chrontel, Texas Instruments: T(bit) = 0.1 * T(Pixel) = 294ps Skew(Intra-Pair) = 0.15 * T(bit)[4][5] = 44.1ps => Δl = v * Δt = 6.62mm ~= 261 mil (Chrontel suggests, without saying why, that matching between signals should be within 5mil.[5] Given the context and calculations above suggesting 261 mil for total, this should probably be 5mil skew per segment.) Intra-pair skew causes EMI.[8] One way to see this is to consider what we're trying to do by routing the differential signal on a differential pair of traces. The goal is to make the distance between the traces as small as possible and still maintain the differential impedance needed to match the rest of the transmission line. This reduces the size of the effective antenna. When the signals are propagating in parallel down this pair of traces the length of the effective dipole antenna is the distance between the two wavefronts. If the traces are parallel and equidistant from the source, the combined wavefront will be perpendicular to the traces and of minimal effective size. If a difference in distance from the source occurs between the traces, the combined wavefront will no longer be perpendicular to the traces and the effective size will be larger. Toradex' "Layout Design Guide" has a great treatment of problems and suggested solutions throughout section 6 "High-Speed Layout Considerations". Of particular interest here is section 6.7 "Length Matching", pp. 21-25. Section 6.8 "Signal Return Path", pp. 25-29, is of considerable related interest. Chamferred Corners (or Trace Bend Geometry) I'm glad to see you are already using 45 degree bends instead of 90 degree corners. This helps the corners maintain the proper impedance. When serpentine traces (meanders) are needed to attain certain lengths of a single-ended trace, make sure individual segment lengths are at least 1.5x the width of the trace. Also, the spacing between parallel segments of the same trace should be at least 4x the width of the trace.[9] Length Matching Differential pair signals should not propagate asynchronously over a distance greater than 15mm[10] = 590mil. Thus the compensation for length mis-matches should be placed as close to the mismatch as possible. Differential traces can be segmented by a connector, pad (component or IC), or via.[10][5] "Each segment of a differential pair connection needs to be matched individually."[10] Ideal serpentine trace geometry for equalizing differential traces consists of the following proportions: the spacing between traces in the meanders should not exceed twice the normal spacing, and the length of more widely spaced traces should not exceed three times the normal trace width.[10, see Figure 23] References: [3] Toradex, page 38 [4] TI, page 4 [5] Chrontel, page 5 [6] https://forum.allaboutcircuits.com/threads/hdmi-inter-intra-pair-skew-inter… [7] https://e2e.ti.com/support/interface/high_speed_interface/f/138/t/267205 [8] https://www.researchgate.net/publication/224650488_Effects_of_skew_on_EMI_f… [9] Toradex, page 17, Figures 12 & 13 [10] Toradex, pages 22-23 Bibliography: http://www.chrontel.com/media/Application%20Notes/AN-B026%20Rev0.2.pdf http://e2e.ti.com/cfs-file/__key/telligent-evolution-components-attachments… http://docs.toradex.com/102492-layout-design-guide.pdf

3 8

HDMI High-Frequency Layout: Speed of Propagation
by Richard Wilbur 01 Aug '17

01 Aug '17

HDMI Layout Notes for EOMA68 Cards by Richard Wilbur Speed of Propagation First let's calculate the speed of electromagnetic wave propagation in a microstrip differential pair on our circuit board. Then we can use that speed to convert the timing tolerances of the HDMI standard into distance tolerances which will guide our priorities in routing the differential pairs. Electromagnetic waves travel at the speed of light. But since the electromagnetic fields of these signals extend between the conductors into both air and the FR-4 substrate of our printed circuit board (PCB), they will not travel at the same speed as if they were travelling through a vacuum. Speed of light in a vacuum: c = 3.00e8 m/s Speed of light in some other substance: v(wave travelling in substance) = c / sqrt(relative permittivity of substance) Since the electromagnetic waves in question propagate partly in air and partly in the PCB substrate (FR-4), we estimate their governing permittivity to be between that of air and FR-4. Speed of propagation for signals conducted in differential microstrip on the PCB: relative permittivity of FR-4 = 4.4 [1] relative permittivity of air = 1 v(in FR-4) = 3.00e8 / sqrt(4.4) = 1.43e8 m/s v(partly in FR-4, partly in air) ~= 3.00e8 / sqrt(4) = 1.5e8 m/s = 150um/ps[2] References: [1] https://en.wikipedia.org/wiki/FR-4 [2] Toradex, page 21 Bibliography: http://docs.toradex.com/102492-layout-design-guide.pdf

1 0

HDMI High-Frequency Layout: Introduction
by Richard Wilbur 01 Aug '17

01 Aug '17

This is a discussion of the considerations when designing and executing a PCB layout containing high-frequency signal traces--specifically in this case HDMI. It is being published to the [arm-netbook] mailing list in several sections dealing with related topics. The original was created in Open Document Text and I have dumped it into Unicode Text in order to accommodate the mailing list. Please let me know if you have any trouble reading the format and I will attempt to remedy the problem. I am releasing the first two sections before I sleep--the remainder after I sleep.

2 2

Re: [Arm-netbook] HDMI v1.4 Audio Return and Ethernet channels
by Andrew Bolin 01 Aug '17

01 Aug '17

> > so *i'm* not quotes considering it quotes - if it's there and there's > a linux kernel module it's there, people can compile it and use it. > > l. > Can't use it if the pin has no connection to the CPU! In the last screenshots I saw ( http://hands.com/~lkcl/eoma/a20_hdmi_review/scrn2.png ), pin 2 HEAC+ (ethernet/ARC) is not connected to anything. Pin 1 (HEAC- & HPD) does go somewhere, but it's of no use for these functions by itself. CEC does seem to be routed and is mentioned on the A20 info page. No SBC that I've seen actually uses these functions (unfortunately). - Andrew.

3 2

HDMI v1.4 Audio Return and Ethernet channels
by Richard Wilbur 01 Aug '17

01 Aug '17

Luke, Have you considered using the Audio Return channel in HDMI v1.4 to send digital multi-channel sound back to the EOMA68-A20? How about the Ethernet channel (also in HDMI v1.4)? Does the processor support these? They are optional capabilities of HDMI v1.4 and I only ask because it would change the routing. Sincerely, Richard

2 5

Rv: Update: 2.7.4 EOMA68-A20 Cards Arrived
by el_gallo_azul 31 Jul '17

31 Jul '17

I'd be happy enough to supply my own MicroSD card (in place of the TSSOP-48 NAND IC). Greg Flint #yiv0042324540 body, #yiv0042324540 #yiv0042324540bodyTable, #yiv0042324540 #yiv0042324540bodyCell{min-height:100% !important;margin:0;padding:0;width:100% !important;}#yiv0042324540 table{border-collapse:collapse;}#yiv0042324540 img, #yiv0042324540 a img{border:0;outline:none;text-decoration:none;}#yiv0042324540 h1, #yiv0042324540 h2, #yiv0042324540 h3, #yiv0042324540 h4, #yiv0042324540 h5, #yiv0042324540 h6{margin:0;padding:0;}#yiv0042324540 p{margin:1em 0;padding:0;}#yiv0042324540 a{word-wrap:break-word;}#yiv0042324540 .yiv0042324540ReadMsgBody{width:100%;}#yiv0042324540 .yiv0042324540ExternalClass{width:100%;}#yiv0042324540 .yiv0042324540ExternalClass, #yiv0042324540 .yiv0042324540ExternalClass p, #yiv0042324540 .yiv0042324540ExternalClass span, #yiv0042324540 .yiv0042324540ExternalClass font, #yiv0042324540 .yiv0042324540ExternalClass td, #yiv0042324540 .yiv0042324540ExternalClass div{line-height:100%;}#yiv0042324540 table, #yiv0042324540 td{}#yiv0042324540 #yiv0042324540outlook a{padding:0;}#yiv0042324540 img{}#yiv0042324540 body, #yiv0042324540 table, #yiv0042324540 td, #yiv0042324540 p, #yiv0042324540 a, #yiv0042324540 li, #yiv0042324540 blockquote{}#yiv0042324540 #yiv0042324540templatePreheader, #yiv0042324540 #yiv0042324540templateHeader, #yiv0042324540 #yiv0042324540templateBody, #yiv0042324540 #yiv0042324540templateFooter{min-width:100%;}#yiv0042324540 #yiv0042324540bodyCell{padding:20px;}#yiv0042324540 .yiv0042324540mcnImage{vertical-align:bottom;}#yiv0042324540 .yiv0042324540mcnTextContent img{min-height:!important;}#yiv0042324540 body, #yiv0042324540 #yiv0042324540bodyTable{background-color:#F2F2F2;}#yiv0042324540 #yiv0042324540bodyCell{border-top:0;}#yiv0042324540 #yiv0042324540templateContainer{border:0;}#yiv0042324540 h1{color:#606060;display:block;font-family:Helvetica;font-size:40px;font-style:normal;font-weight:bold;line-height:125%;letter-spacing:-1px;margin:0;text-align:left;}#yiv0042324540 h2{color:#404040;display:block;font-family:Helvetica;font-size:26px;font-style:normal;font-weight:bold;line-height:125%;letter-spacing:-.75px;margin:0;text-align:left;}#yiv0042324540 h3{color:#606060;display:block;font-family:Helvetica;font-size:18px;font-style:normal;font-weight:bold;line-height:125%;letter-spacing:-.5px;margin:0;text-align:left;}#yiv0042324540 h4{color:#808080;display:block;font-family:Helvetica;font-size:16px;font-style:normal;font-weight:bold;line-height:125%;letter-spacing:normal;margin:0;text-align:left;}#yiv0042324540 #yiv0042324540templatePreheader{background-color:#FFFFFF;border-top:0;border-bottom:2px solid #f2f2f2;}#yiv0042324540 .yiv0042324540preheaderContainer .yiv0042324540mcnTextContent, #yiv0042324540 .yiv0042324540preheaderContainer .yiv0042324540mcnTextContent p{color:#606060;font-family:Helvetica;font-size:11px;line-height:125%;text-align:left;}#yiv0042324540 .yiv0042324540preheaderContainer .yiv0042324540mcnTextContent a{color:#00b2ad;font-weight:normal;text-decoration:none;}#yiv0042324540 #yiv0042324540templateHeader{background-color:#FFFFFF;border-top:0;border-bottom:2px solid #f2f2f2;}#yiv0042324540 .yiv0042324540headerContainer .yiv0042324540mcnTextContent, #yiv0042324540 .yiv0042324540headerContainer .yiv0042324540mcnTextContent p{color:#606060;font-family:Helvetica;font-size:15px;line-height:150%;text-align:left;}#yiv0042324540 .yiv0042324540headerContainer .yiv0042324540mcnTextContent a{color:#00b2ad;font-weight:normal;text-decoration:underline;}#yiv0042324540 #yiv0042324540templateBody{background-color:#FFFFFF;border-top:0;border-bottom:0;}#yiv0042324540 .yiv0042324540bodyContainer .yiv0042324540mcnTextContent, #yiv0042324540 .yiv0042324540bodyContainer .yiv0042324540mcnTextContent p{color:#606060;font-size:12px;line-height:150%;text-align:left;}#yiv0042324540 .yiv0042324540bodyContainer .yiv0042324540mcnTextContent a{color:#00b2ad;font-weight:normal;text-decoration:none;}#yiv0042324540 #yiv0042324540templateFooter{background-color:#FFFFFF;border-top:2px solid #f2f2f2;border-bottom:0;}#yiv0042324540 .yiv0042324540footerContainer .yiv0042324540mcnTextContent, #yiv0042324540 .yiv0042324540footerContainer .yiv0042324540mcnTextContent p{color:#606060;font-family:Helvetica;font-size:11px;line-height:125%;text-align:left;}#yiv0042324540 .yiv0042324540footerContainer .yiv0042324540mcnTextContent a{color:#00b2ad;font-weight:normal;text-decoration:none;}@media screen and (max-width:480px){#yiv0042324540 body, #yiv0042324540 table, #yiv0042324540 td, #yiv0042324540 p, #yiv0042324540 a, #yiv0042324540 li, #yiv0042324540 blockquote{}}@media screen and (max-width:480px){#yiv0042324540 body{width:100% !important;min-width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 td[id=yiv0042324540yiv7036040991yiv7457952086bodyCell]{padding:10px !important;}}@media screen and (max-width:480px){#yiv0042324540 table[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContentContainer]{width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 .yiv0042324540mcnBoxedTextContentContainer{max-width:100% !important;min-width:100% !important;width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 table[class=yiv0042324540yiv7036040991yiv7457952086mcpreview-image-uploader]{width:100% !important;display:none;}}@media screen and (max-width:480px){#yiv0042324540 img[class=yiv0042324540yiv7036040991yiv7457952086mcnImage]{width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 table[class=yiv0042324540yiv7036040991yiv7457952086mcnImageGroupContentContainer]{width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageGroupContent]{padding:9px !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageGroupBlockInner]{padding-bottom:0 !important;padding-top:0 !important;}}@media screen and (max-width:480px){#yiv0042324540 tbody[class=yiv0042324540yiv7036040991yiv7457952086mcnImageGroupBlockOuter]{padding-bottom:9px !important;padding-top:9px !important;}}@media screen and (max-width:480px){#yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table[class=yiv0042324540yiv7036040991yiv7457952086mcnCaptionBottomContent]{width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table[class=yiv0042324540yiv7036040991yiv7457952086mcnImageCardRightTextContentContainer]{width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 td .yiv0042324540filtered99999 , #yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageCardRightImageContent]{padding-right:18px !important;padding-left:18px !important;padding-bottom:0 !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageCardBottomImageContent]{padding-bottom:9px !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageCardTopImageContent]{padding-top:18px !important;}}@media screen and (max-width:480px){#yiv0042324540 td .yiv0042324540filtered99999 , #yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageCardRightImageContent]{padding-right:18px !important;padding-left:18px !important;padding-bottom:0 !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageCardBottomImageContent]{padding-bottom:9px !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnImageCardTopImageContent]{padding-top:18px !important;}}@media screen and (max-width:480px){#yiv0042324540 table .yiv0042324540filtered99999 td .yiv0042324540filtered99999 , #yiv0042324540 table[class=yiv0042324540yiv7036040991yiv7457952086mcnCaptionRightContentOuter] td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent]{padding-top:9px !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnCaptionBlockInner] table[class=yiv0042324540yiv7036040991yiv7457952086mcnCaptionTopContent]:last-child td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent]{padding-top:18px !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnBoxedTextContentColumn]{padding-left:18px !important;padding-right:18px !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent]{padding-right:18px !important;padding-left:18px !important;}}@media screen and (max-width:480px){#yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table .yiv0042324540filtered99999 , #yiv0042324540 table[id=yiv0042324540yiv7036040991yiv7457952086templateFooter]{max-width:600px !important;width:100% !important;}}@media screen and (max-width:480px){#yiv0042324540 h1{font-size:24px !important;line-height:125% !important;}}@media screen and (max-width:480px){#yiv0042324540 h2{font-size:20px !important;line-height:125% !important;}}@media screen and (max-width:480px){#yiv0042324540 h3{font-size:18px !important;line-height:125% !important;}}@media screen and (max-width:480px){#yiv0042324540 h4{font-size:16px !important;line-height:125% !important;}}@media screen and (max-width:480px){#yiv0042324540 table .yiv0042324540filtered99999 td .yiv0042324540filtered99999 , #yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086mcnBoxedTextContentContainer] td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent] p{font-size:18px !important;line-height:125% !important;}}@media screen and (max-width:480px){#yiv0042324540 table[id=yiv0042324540yiv7036040991yiv7457952086templatePreheader]{display:block;}}@media screen and (max-width:480px){#yiv0042324540 td .yiv0042324540filtered99999 td .yiv0042324540filtered99999 , #yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086preheaderContainer] td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent] p{font-size:14px !important;line-height:115% !important;}}@media screen and (max-width:480px){#yiv0042324540 td .yiv0042324540filtered99999 td .yiv0042324540filtered99999 , #yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086headerContainer] td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent] p{font-size:18px !important;line-height:125% !important;}}@media screen and (max-width:480px){#yiv0042324540 td .yiv0042324540filtered99999 td .yiv0042324540filtered99999 , #yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086bodyContainer] td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent] p{font-size:18px !important;line-height:125% !important;}}@media screen and (max-width:480px){#yiv0042324540 td .yiv0042324540filtered99999 td .yiv0042324540filtered99999 , #yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086footerContainer] td[class=yiv0042324540yiv7036040991yiv7457952086mcnTextContent] p{font-size:14px !important;line-height:115% !important;}}@media screen and (max-width:480px){#yiv0042324540 td[class=yiv0042324540yiv7036040991yiv7457952086footerContainer] a[class=yiv0042324540yiv7036040991yiv7457952086utilityLink]{display:block;}}

9 50

Broadcom BCM2837 100% libre now ?
by Bill Kontos 31 Jul '17

31 Jul '17

Open firmware seems to be available here for a minimal boot. I have no idea if this is reverse engineered or provided by Broadcom, it seems like broadcom has at least released all the headers under some bsd-like license. The firmware here is gplv2+. https://github.com/christinaa/rpi-open-firmware Here is a report of someone booting using only the free firmware dated Jan 2017 while the most recent commits are from April. http://crna.cc/b/11 If I recall correctly the kernel driver was already open-sourced in 2014. The VC4 mesa driver made and upstreamed by a broadcom emploee here. I'm kind of confused since the vpu has to be used for the rpi to boot even if you don't want video acceleration, but this is an foss drm driver for the vc4 silicon only... what's going on with the part of the blob that used to do the initialization? https://github.com/anholt/mesa/wiki/VC4 And some documentation https://www.kernel.org/doc/html/latest/gpu/vc4.html Is this enough ? Or close to enough for a fully libre BCM2837 system to make it worth taking a look ? It seems like with the community around the rpi any bugs etc would be very easy to spot and squash in the future. I still don't know what's going on with the wifi in that SoC and I won't pretend that I understand everything I just wrote, but it certainly seems like there has been some movement from the "the 2mb userland blob does everything" stage. I found somewhere that board schematics still require an nda though.

2 1

Jump to page:

2025

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

arm-netbook