CIOUT kept the byte to send next in BSOUR ($95), but iec_tx_byte, which
CIOUT and iec_tx_flush (called by UNLSN, UNTLK, LISTEN, TALK) use to
send it, transmits TBTCNT ($A4). So every byte CHROUT sent to a serial
device was whatever TBTCNT held, and a file written with CHKOUT and
CHROUT held the wrong bytes.
The contract (C64 Programmer's Reference Guide, CIOUT): CIOUT sends a
byte to the listening device, always holding one back so that the last
byte goes with EOI when UNLSN ends the transfer. CIOUT now buffers the
byte in TBTCNT, the one-line fix of upstream PR #113; changing the send
path to read BSOUR would also move LOAD's and SAVE's bytes.
Upstream: https://github.com/MEGA65/open-roms/pull/113
chris
264e9792a5