infokindle
Changing a Kindle into a Kindle information display (that refreshes the screen on a defined scheduled).
CHANGES
added USE_SMTP: toggle on/off sending log via SMTP
added USE_WAN: toggle on/off using a WAN connection
added USE_NTP: toggle on/off updating time with NTP
renamed download_lib to download_new_img: renamed with a more appropriate name
This project is extended from the avakindle project. GREAT KUDOS GOES OUT TO THE ORIGINAL AUTHOR. I've generalized his code for a slightly different purpose. I'm attaching the original readme below:
avakindle
Remote public warning display based on amazon kindle DX with OS version 2.5.8
For more information, visit: snowtechblog.wordpress.com
TODO'S
TODO: Add serverside script
TODO: list and explain futur improvements
TODO: Links, code formatting
TODO: Add start script, find it (on the kindle?)
TODO: add more comments to source code
Source description:
The code is devided into three sections. The first block are function definitions. The second block are variables, initialize the WAN module and logfile, as well as defines that Kindle downloads the image on startup. The third block is the infinite while loop. OK, lets go through the third block to understand the logic ,-)
Note: You must set your username $MAIL_USER, passwort $MAIL_PW, email address $MAIL_ADD and recipient mail address $MAIL_RECIPIENT to get the send_log working.
Startup:
Open a terminal on Kindle (you should know how to do this, otherwise (LINK MOBILEREAD) is your friend...). Start the code with redirecting all possible output, cause this will write over the fullscreen image:
(FIND THE FILE ON KINDLE: START_LLB.SH or similar...)
Before entering the loop, function WAIT_FOR_SS will cause a wait until state screensave is reached (remove USB cable! slide power button once to go to screensave manually). At the startup the variable $DOWNLOAD_IMG will be set to YES, but lets neglect that for the moment, so its value is NO. So the code jumps into the function WAIT_FOR_READY.
WAIT_FOR_READY:
This is acually the heart of the loop, its doing much more than just wait. It waits until the state "Ready to suspend" and then calls the function to calculate the next wakeup (calc_wakeup) and to write the wakeup value to the RTC (write_wakeup).
The trick with the $AWAKE_AGAIN variable is to ensure that the function to calculate and to write the wakeup time is only called once and not multiple times (remember the state "ready to suspend" is 5 seconds long and I experienced that writing the wakeup time to often to the RTC can cause a failure and Kindle is in gone to never ending sleep). So always when Kindle is in a state where grep does not find anything with "Ready" (all other states), the $AWAKE_AGAIN is set to YES and as soon as entering "Ready" there are 5 seconds to perform calc_wakeup and write_wakeup.
CALC_WAKEUP:
This checks the actions and calculates the next wakeup. There are three possibilities. 1st: The last download try failed (file not found on server, not connection etc.) and $DL_FAILED is YES, so Kindle will try in $WAKEUP_CHECK_DEFAULT_FAIL (def=600) seconds again. If $DL_FAILED is NO, we calculate the $DIFF_TIME which is the time between next action and the current time. If the $DIFF_TIME is larger than the $WAKEUP_CHECK_DEFAULT (def=3600) seconds, Kindle will wake up again in this time. If $DIFF_TIME is smaller, Kindle needs to consider to sleep again or to start the download. Note 1: the Kindle never wakes up excatly on time, so there is a time window ($STAY_AWAKE def=240sec) when to consider an action to be ready to download. Note 2: Better never try to sleep for less than 60 seconds (or 120 seconds?), remember that the wakeup process takes at least a minute in screensaver state.
In any case, the output of $CALC_WAKEUP will be a new value for the variable to trigger the download $DOWNLOAD_IMG and the next wakeup time $WAKE_TIME. The $WAKE_TIME will be used in write_wakeup:
WRITE_WAKEUP:
Write the wakeup time to the RTC. First checks that $WAKE_TIME contains a reasonable value, that is $WAKE_TIME larger than $WAKEUP_MINIMAL (def=60sec) and that we have enough time to set the wakeup, that is $TIME_LEFT in "Ready for Suspend" is larger than $LATEST_WAKEUP_SET (def=0sec, we have to risk everything to try to write the wakeup ...). If Kindle should download the image (this is done in Active state), we dont want to write a wakeup (could be in conflict with switching the state) but bring the kindle into active (NOTE: this should not be done by powerd_test -p without any state checking, cause this can make a lot of trouble... definitely a point to improve!).
OK, now Kindle wakes up $WAKEUP_CHECK_DEFAULT (every hour) and on specific times defined in $ACTION (space separated string of time, in my case two actions per day always at 08:15 and 17:15). Now, when an Action is active, variable $DOWNLOAD_IMG is set to YES and the conditional in the infinite loop is entered. Remember that we enter in Screensave mode (hopefully), so wait_for_ss will not delay. Then, we switch into active to have 10minute to perform all the stuff we want Kindle to do in the action. In my case its defined in DOWNLOAD_LLB.
DOWNLOAD_LLB:
Turns WAN on, checks for connection, download image, sync the time and sends the logfile via email. If its not possible to get connection, set_retries is called to count the number of retries. To prevent from checking infinitely long every ten minutes for a download, the retries are limited to the number $DL_RETRIES (def=3). This results in $DL_FAILED=YES for the next run of calc_wakeup. If Kindle is able to connect, the task mentioned are performed. For the download server set the variable $IMG_URL to your needs. Note that Kindles version of wget does not support to check for a never file. This would be a nice-to-have. So a second improvement goes into that direction ...
SEND_LOG:
send_log need some special notes. Kindle does not give a mail agent, so I use sendmail from a recent busybox compilation. I found that a precompiled ARM7L version works on kindle (LINK???). You need to specify the path to it in the function. And you need to setup the sendmail command to work with your provide, e.g. set the variables $MAIL_USER, $MAIL_PW, $MAIL_ADD and $MAIL_RECIPIENT to your values.
DISPLAY_IMAGE:
Last and least, we need to display the downloaded image with display_image. This is done with Kindles internal command eips. Since my project should work in the cold, Kindle runs eips several times in hope that the eInk display gets better contrast by writing the pixels several times.