Fail to install stretch to iMac G5

[Matti Palmström <mattip.debian@gmail.com>]

I have an iMac G5 iSight with a 64-bit PowerPC 970fx that I try to install Stretch to. I have downloaded debian-stretch-DI-rc5-ppc64el-netinst.iso and burned it to a cd and dd'ed it to a usb stick.

Neither is detected by the mac boot thingie when boot with with option key pressed.

I've tried booting through open firmware. By the look of the install media I assume it uses grub these days so I've tried with just

0 > boot usb0,\install

a screen saying "loading XCOFF" flickers by and then I get the circle with the slash. I've also tried \install\vmlinux and many other variants. Anyone know what I've missed?

Regards

/M