{"id":483,"date":"2011-06-24T14:07:22","date_gmt":"2011-06-24T21:07:22","guid":{"rendered":"http:\/\/blog.mezeske.com\/?p=483"},"modified":"2011-06-24T16:04:16","modified_gmt":"2011-06-24T23:04:16","slug":"boot-a-kernel-over-serial-with-u-boot-and-kermit","status":"publish","type":"post","link":"http:\/\/blog.mezeske.com\/?p=483","title":{"rendered":"Boot a Kernel over Serial with U\u2011Boot and Kermit"},"content":{"rendered":"

I\u2019m doing a lit\u00adtle bit of work that involves fre\u00adquent\u00adly rebuild\u00ading the Linux ker\u00adnel and installing it on a head\u00adless ARM<\/span> board. The par\u00adtic\u00adu\u00adlar ARM<\/span> board I\u2019m work\u00ading with has some ven\u00addor sup\u00adport for flash\u00ading ker\u00adnels, but it\u2019s slow and clunky, and I have to run it inside a Windows XP<\/span> VM<\/span>. The ARM<\/span> board uses the U\u2011Boot boot\u00adloader, though, so it\u2019s pos\u00adsi\u00adble to boot the ker\u00adnel in a cou\u00adple of dif\u00adfer\u00adent ways. One way would be to load the ker\u00adnel via TFTP<\/span>, but I haven\u2019t got\u00adten that work\u00ading yet on my board. The oth\u00ader option is to load it via ser\u00adi\u00adal, which isn\u2019t very fast but requires very lit\u00adtle setup.<\/p>\n

U\u2011Boot\u2019s loadm<\/em> com\u00admand allows a ker\u00adnel to be loaded, via ser\u00adi\u00adal, into a mem\u00ado\u00adry loca\u00adtion. The bootm<\/em> com\u00admand may then be used to boot the ker\u00adnel direct\u00adly, which saves time com\u00adpared to writ\u00ading the ker\u00adnel to the flash mem\u00ado\u00adry and load\u00ading it from there. The trou\u00adble is that loadm<\/em> expects the ker\u00adnel to be sent via the Kermit pro\u00adto\u00adcol. I found a few exam\u00adples of how to deal with Kermit, but none of them direct\u00adly applied to load\u00ading a ker\u00adnel with U\u2011Boot.<\/p>\n

I came up with the fol\u00adlow\u00ading Kermit script to solve my prob\u00adlem. This script auto\u00admat\u00adi\u00adcal\u00adly waits for the board to reset, sends the loadm<\/em> com\u00admand, push\u00ades down the ker\u00adnel, and runs it via the bootm<\/em> com\u00admand. After it boots the ker\u00adnel, it turns into an inter\u00adac\u00adtive con\u00adsole. This script relies on C\u2011Kermit, which I installed under Ubuntu as follows:<\/p>\n

bash$ <\/span>sudo<\/span> aptitude install<\/span> ckermit<\/div><\/div>\n

The script I\u2019m using is as fol\u00adlows. There are a lot of set\u00adtings hard-cod\u00aded into the script, so read the com\u00adments care\u00adful\u00adly to deter\u00admine what parts you might need to change to suit your set\u00adup. To use this script, sim\u00adply copy it into a file named, for exam\u00adple, boot-ker\u00adnel<\/em>, give it exe\u00adcutable per\u00admis\u00adsions, and run it.<\/p>\n

#!\/usr\/bin\/kermit<\/span>
\n
\n# Serial port setup.  These settings will likely need to be<\/span>
\n# changed to match the configuration of your workstation<\/span>
\n# and the ARM board you're working with.<\/span>
\nset<\/span> line \/<\/span>dev\/<\/span>ttyUSB0
\nset<\/span> speed 115200<\/span>
\nset<\/span> serial 8n1
\n
\n# General C-Kermit settings.  These probably don't need to change.<\/span>
\nset<\/span> flow-control none
\nset<\/span> file<\/span> type<\/span> bin
\nset<\/span> carrier-watch off
\nset<\/span> prefixing all
\nset<\/span> modem none
\n
\necho<\/span> \"Prepared to boot new kernel.  Reset the board now.\"<\/span>
\n
\n# This is the string that my board outputs to allow the user to<\/span>
\n# gain access to the U-Boot console.  Change this to suit your<\/span>
\n# setup.<\/span>
\ninput 60<\/span> \"Hit SPACE to stop autoboot\"<\/span>
\n# If your board wants you to press a different key to get to<\/span>
\n# U-Boot, edit this line.<\/span>
\noutput \" \"<\/span>
\ninput 5<\/span> \"u-boot>\"<\/span>
\n# Here, 0x800000 is the memory address into which the kernel<\/span>
\n# should be loaded.<\/span>
\nlineout \"loadb 0x800000\"<\/span>
\n# This should be the absolute path to your kernel uImage file.<\/span>
\nsend \/<\/span>path\/<\/span>to\/<\/span>uImage
\ninput 5<\/span> \"u-boot>\"<\/span>
\nlineout \"bootm 0x800000\"<\/span>
\n
\n# This command drops you into a console where you can interact<\/span>
\n# with the kernel.<\/span>
\nconnect<\/div><\/div>\n

Once the script has giv\u00aden you con\u00adsole con\u00adtrol, you need to use the Kermit escape key to exit. By default, this is set to Ctrl+\\<\/em> (that\u2019s a back\u00adslash). To see a list of com\u00admands, type Ctrl+\\<\/em> and then ?<\/em>. The com\u00admand to imme\u00addi\u00adate\u00adly exit the con\u00adsole is q<\/em>.<\/p>\n

One last thing to note: this script does\u00adn\u2019t do any error check\u00ading. Each of the input<\/em> com\u00admands can fail, if it does not see the text it\u2019s look\u00ading for in the spec\u00adi\u00adfied time. The script could be extend\u00aded to check for errors using Kermit\u2019s IF<\/span><\/em> command.<\/p>\n","protected":false},"excerpt":{"rendered":"

I\u2019m doing a lit\u00adtle bit of work that involves fre\u00adquent\u00adly rebuild\u00ading the Linux ker\u00adnel and installing it on a head\u00adless ARM<\/span> board. The par\u00adtic\u00adu\u00adlar ARM<\/span> board I\u2019m work\u00ading with has some ven\u00addor sup\u00adport for flash\u00ading ker\u00adnels, but it\u2019s slow and clunky, and I have to run it inside a Windows XP<\/span> VM<\/span>. The ARM<\/span> board [\u2026]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"wp_typography_post_enhancements_disabled":false},"categories":[3],"tags":[5,33,32],"_links":{"self":[{"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=\/wp\/v2\/posts\/483"}],"collection":[{"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=483"}],"version-history":[{"count":21,"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=\/wp\/v2\/posts\/483\/revisions"}],"predecessor-version":[{"id":504,"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=\/wp\/v2\/posts\/483\/revisions\/504"}],"wp:attachment":[{"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=483"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=483"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/blog.mezeske.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=483"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}