On Sun, 29 Aug 2021 at 11:05, Mark Cave-Ayland
<mark.cave-ayland@ilande.co.uk> wrote:
Here is another small set of ESCC fixes from my attempts to boot MacOS on the
q800
machine.
When MacOS loads the OpenTransport extension on boot it attempts to enable
SDLC mode on the ESCC. QEMU's emulation doesn't support SDLC mode, but without
these fixes the active low STATUS_SYNC bit in R_STATUS is continually
asserted causing the extension to hang on startup as it believe it is constantly
receiving LocalTalk responses during its initial negotiation phase.
The ESCC data sheet is the first one I've ever encountered that includes
a multiple-choice test on features of the device ("ESCC Questions and Answers"
on pages 385/386: http://www.zilog.com/docs/serial/scc_escc_um.pdf ) :-)