So the idea of developing on the ATtiny MCU's is very atractive to me as many projects are not that needy of speed or I/O's. I've read the high low tech tutorial but it is not clear about the distiction in burning bootloader and sketch (program). Is it the case that the upload sketch via an ISP programmer burns both at the same time and there is no serial comms as there is no serial port and there is no bootloading ability in the chip ?
Presumably the arduino environment know what to do when you select the board and programmer ?
The "Burn Bootloader" process also sets the configuration fuses. If you want your ATtiny to run at 8 MHz instead of the factory default 1 MHz you need to do the "Burn Bootloader" on it at least once.
You are right that no bootloader is actually written and you need an ISP to load sketches.
Ah I get it so the Bootloading process just set's the chip up the sketch burning process also puts in the support stuff that usually runs in the bootloader
There is no "support stuff that usually runs in the bootloader". The bootloader only copies data from the UART to FLASH and since the ATtiny doesn't have a UART there is nothing for a bootloader to do. The ISP writes the sketch directly to FLASH.
The same thing happens if you use an ISP to write a sketch into an Arduino UNO. The bootloader becomes unreachable and does't do anything. If you want to go back to uploading via USB (and the UART) you have to re-burn the bootloader.
Ah, what dose selecting the AVRISP upload the sketch too ? I always thought that setting only affected the burn boot loader command, does the bootloader still need burning to the UNO MCU to set up the fuses ?
sparkylabs:
Ah, what dose selecting the AVRISP upload the sketch too ? I always thought that setting only affected the burn boot loader command, does the bootloader still need burning to the UNO MCU to set up the fuses ?
The programmer choice in Tools->Programmers is used for both Tools->Burn Bootloader and File->Upload Using programmer