I'm trying to upload the Blink sketch on my ATTiny24A.
I downloaded the tiny library, but there isn't the Attiny24.
In the Arduino forum there's an sketch for the ATTiny24 written by Bare Metal.
After loading the ArduinoISP sketch with the settings AVRISP mkll on my Arduino UNO I connected the ATTiny24.
Then I setted Arduino as ISP.
After that the board was setted on ATTiny24 (1MHz internal osc).
I tried to upload the blink sketch with Shift + Left click on the Upload button and the IDE returned this error:
You have to set an Arduino board
You'll need to modify the boards.txt, or use a version of the core with support for the 24. I don't know of one with sensible 24 options in boards.txt by default (the TCWORLD core than my tiny core is forked from had entries for the 24, but with weird settings) - on pre-1.6.x, people generally didn't include the 24 and 25, because it clogged up the board menu with chips that almost nobody uses (since the savings over 84 is so small, and because 2k goes really fast with arduino sketches).
If you were on 1.6.x, I'd recommend my core (second one in sig), which supports all the x4/x5/etc chips, but that core is 1.6.x only - it uses the new submenu system to support every common clock speed, and any BoD setting on any chip in the series, without a multi-page long board select menu
It's a github repo, not a board manager url (that's not supported yet #3)
See readme at that link+ for install instructions - basically you just download zip and extract into (user)/documents/Arduino/hardware or just sync the repo to there if you prefer that (makes it easier to update - I've been updating it several times a week, as people find bugs with the more exotic chips and I fix them) .