Re: [avrdude-dev] USBasp improvements

[Joerg Wunsch]

As Thomas Fischl wrote:

> In USBasp firmware the slow SCK option is currently implemented in
> software to get very low frequency (8kHz). Is such a low frequency
> actually needed? If 187.5kHz is slow enough for all targets we can
> drop this software implementation and use only the hardware ISP.

You can never get too slow. :-) You could have a device being clocked
from a 32 kHz crystal oscillator, and with a CKDIV8 fuse programmed,
so the resulting CPU clock frequency were 4096 Hz.  In that case, the
ISP clock must be below 1024 Hz... (and be it only in order to
unprogram the mistakenly programmed CKDIV8 fuse again :).

But for the more realistic case that someone is using the internal
(nominally 128 kHz) RC oscillator as the CPU clock, the ISP clock
frequency would be limited to < 32 kHz.

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)