{"id":300,"date":"2016-07-04T16:07:51","date_gmt":"2016-07-04T21:07:51","guid":{"rendered":"http:\/\/charles-oneill.com\/blog\/?p=300"},"modified":"2020-08-29T11:31:13","modified_gmt":"2020-08-29T16:31:13","slug":"gps-waas-update-magellan-sportrak","status":"publish","type":"post","link":"https:\/\/charles-oneill.com\/blog\/gps-waas-update-magellan-sportrak\/","title":{"rendered":"GPS WAAS Update (Magellan Sportrak)"},"content":{"rendered":"

Today, we manipulate bits to resurrect a hobbled 15 year old GPS receiver. In the process, I learned about WAAS and s-records to successfully update a client’s  Magellan Sportrak GPS unit.<\/p>\n

\"calc\"<\/a><\/p>\n

\"waas_sats\"<\/a><\/p>\n

<\/p>\n

GPS and WAAS<\/strong><\/p>\n

The first part of this project requires an understanding of the global positioning system (GPS) and the Earth’s atmosphere.<\/p>\n

http:\/\/www.nstb.tc.faa.gov\/RTData_WaasSatelliteData.htm<\/a><\/p>\n

https:\/\/en.wikipedia.org\/wiki\/Wide_Area_Augmentation_System<\/a><\/p>\n

Magellan GPS
\n<\/strong><\/p>\n

The Magellan GPS receiver used older WAAS data. Specifically, INMARSAT 3-F2 (aka. PRN 120) and INMARSAT 3-F4 (aka. PRN 122 AOR-W) were hard coded into the GPS unit. These ceased WAAS service and were not replicated.<\/p>\n

You can verify which WAAS satellites are being used by entering the secret [menu][left][right][left][right] 03 menu.<\/p>\n

S-Records<\/strong><\/p>\n

Directly updating the GPS firmware is required.<\/p>\n

https:\/\/en.wikipedia.org\/wiki\/SREC_(file_format)<\/a><\/p>\n

I created an Excel document to assist the firmware modification process: STPS-v1<\/a><\/p>\n

A 7z compressed update file for only<\/strong> the Magellan SportTrak is available at: spor534-WAASco<\/a><\/p>\n

 <\/p>\n

Client’s Response<\/strong><\/p>\n

The client responded with the following<\/p>\n

You did it!!  Your update works just fine.  SporTrak now shows WAAS when moving and WAAS AVERAGING when stopped.  I misquoted the # of satellites it is capable of receiving:  the screen shows space for 12 and I got 11 at one time this AM!!   Apparently this version does not show EPE except when it cannot view a WAAS satellite.  But I can tell from the displayed elevation that the precision is greatly improved.<\/p><\/blockquote>\n

 <\/p>\n\n\n

Update: 29 August 2020. In response to an emailed question about line checksums, I revisited this project. Enclosed is a portion of my response. <\/p>\n\n\n\n


I only modified the 6 GPS numbers. The GPS locations were kept the same, as an updated ephemeris should be (and was)\u00a0received on startup.

Original:\u00a0 7A<\/strong>00FFF1 \u00a078<\/strong>000040\u00a0 83<\/strong>0000B2\u00a0 86<\/strong>00008C\u00a0\u00a081<\/strong>00008C\u00a0 89<\/strong>000000
Updated: 87<\/strong>00FFF1\u00a0 8A<\/strong>000040\u00a0 85<\/strong>0000B2\u00a0 0A<\/strong>00008C\u00a0 0D<\/strong>00008C\u00a0 1E<\/strong>000000

Once you find the right spot in the hex file, this is an almost embarrassingly trivial change. But it’s worth the cost and use of the GPS unit.

It turns out that the Magellan does not use the checksums. Surprising but true.

<\/td><\/tr><\/tbody><\/table><\/figure>\n","protected":false},"excerpt":{"rendered":"

Today, we manipulate bits to resurrect a hobbled 15 year old GPS receiver. In the process, I learned about WAAS and s-records to successfully update a client’s  Magellan Sportrak GPS unit.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/posts\/300"}],"collection":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/comments?post=300"}],"version-history":[{"count":10,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/posts\/300\/revisions"}],"predecessor-version":[{"id":1540,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/posts\/300\/revisions\/1540"}],"wp:attachment":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/media?parent=300"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/categories?post=300"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/tags?post=300"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}