/* SPDX-License-Identifier: GPL-2.0 */
/*
 * iec_timing.h - starting timing constants for the listener handshake.
 *
 * Cross-referenced from the IEC spec, sd2iec empirical values, and ninepin /
 * raspbiec observed values. See the "Starting Constants Table" and §1.7 of
 * _research/pi-kernel-module-rt-gpio-2026-06-18.md. Tune in Phase 2 against a
 * real C64 / logic analyser.
 */
#ifndef _IEC_TIMING_H
#define _IEC_TIMING_H

/* Per-CLK-transition busy-poll timeout. Generous; abort the byte and report a
 * frame error if a CLK edge does not arrive within this window. Bounds the
 * IRQ-off interval at ~8 ms worst case (8 bits), ~200 us in the normal case. */
#define IEC_CLK_TIMEOUT_US   1000

/* EOI detection: after releasing DATA (ready-for-data), if CLK does not assert
 * within this window the talker is signalling EOI. Spec >= 200 us; sd2iec uses
 * 256 us. We use 250 us (+25% margin over spec). */
#define IEC_EOI_DETECT_US    250

/* EOI acknowledge hold: pull DATA low for this long to ack EOI. Spec (Tei)
 * >= 60 us; sd2iec uses 73 us (AVR instruction-calibrated). Pi A53 is faster;
 * 80 us gives margin. */
#define IEC_EOI_ACK_HOLD_US  80

/* Glitch filter window for sense-line reads. A level change is only believed
 * once it has held this long; a shorter pulse is treated as noise. Matches a
 * confirmed-working reference listener (5 us). sd2iec / the 1571 ROM
 * use a comparable few-microsecond debounce. Far shorter than a real IEC bit
 * (tens of us), so it never smears valid data. */
#define IEC_DEBOUNCE_US      5

/* Between-bytes minimum hold before the talker releases CLK for the next byte
 * (Tbb). We simply wait for the next CLK transition; this is documentary. */
#define IEC_BETWEEN_BYTES_US 100

/*
 * ATN response (Tat <= 1000 us) is NOT a udelay: it is performed by the ATN
 * falling-edge ISR pulling DATA low immediately (hardirq latency ~5-20 us on
 * the A53). Byte acknowledge (Tf <= 1000 us) is likewise immediate -- a single
 * GPIO write at the end of the IRQ-off bit loop.
 */

#endif /* _IEC_TIMING_H */