Pressing Z returned "net-update failed (-2)" -- ring_next() rejecting an RRP
outside the ring (pages 1-15) before a single frame was read.
The pointer was never ours to assume. Swiss initialises the BBA before
launching us and writes RRP itself, and an NCRA reset does NOT restore the
register file's copy of either pointer: their init values only apply at FPGA
configuration. So RRP can legitimately be anything on entry, including 0,
and the previous code treated that as a fatal error instead of a state to
establish.
netboot_receive() now reads RWP and writes RRP = RWP after the reset, which
declares the ring empty and consistent whatever it was, so the first frame
read is genuinely the host's first block. RWP itself is still checked,
because that one IS the gateware's own pointer and an out-of-range value there
would be a real fault rather than inherited state.
The ring-error message now reports RRP and RWP and spells out which of the
three failures it was (EXI access, RRP out of range, implausible descriptor).
Each test costs an SD card copy by hand, so a bare error code is not worth the
round trip.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Roflin
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