mirror of
https://github.com/RetroPortingToolKit/psxrecomp
synced 2026-10-28 19:07:47 -04:00
Alex Vanderveen
83 lines
3.6 KiB
C
83 lines
3.6 KiB
C
/*
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* psx_link.h -- abstract serial-link endpoint for the SIO1 device.
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*
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* An endpoint is "the far side of the cable" as seen by one SIO1 block:
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* push a finished character onto the wire, poll characters whose delivery
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* cycle has arrived, and exchange the DTR/DSR + RTS/CTS handshake lines.
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*
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* ===== DETERMINISM CONTRACT (load-bearing, do not relax) =====
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* Every op is a pure function of endpoint state and the guest-cycle argument:
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* - no wall-clock, no threads, no socket I/O inside any op;
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* - rx/rx_peek/get_lines are idempotent for a fixed (state, cycle);
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* - characters carry a due_cycle stamped on the GUEST timeline at tx();
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* rx() releases an entry only once now >= due_cycle;
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* - snapshots serialize due_cycle as a DELTA from the passed guest cycle
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* (absolute cycles fork after a clock restore).
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* A future socket backend must ingest bytes on the netplay path at an agreed
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* guest-cycle boundary and stamp due_cycle from the agreed schedule, leaving
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* rx() a pure ring drain. This is what keeps SIO1 rollback/savestate safe.
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*/
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#ifndef PSX_LINK_H
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#define PSX_LINK_H
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#include <stdint.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* Local outputs (set_lines). */
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#define PSX_LINK_DTR (1u << 0) /* local DTR -> peer DSR */
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#define PSX_LINK_RTS (1u << 1) /* local RTS -> peer CTS */
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/* Remote inputs (get_lines). */
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#define PSX_LINK_DSR (1u << 0) /* peer DTR */
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#define PSX_LINK_CTS (1u << 1) /* peer RTS */
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typedef struct PsxLinkOps {
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/* Shift one finished character onto the wire. `cycle` is the guest cycle
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* at which the transmit shift completed. Returns 1 if the wire took it,
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* 0 if it was discarded (no cable). */
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int (*tx)(void *self, uint8_t byte, uint64_t cycle);
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/* Pop the next character with due_cycle <= `cycle`. Returns 1/0. */
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int (*rx)(void *self, uint8_t *out, uint64_t cycle);
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/* Non-consuming: due_cycle of the oldest queued inbound character.
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* Returns 1 and writes *due, or 0 if the inbound queue is empty. */
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int (*rx_peek)(void *self, uint64_t *due);
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void (*set_lines)(void *self, uint32_t out_lines); /* PSX_LINK_DTR/RTS */
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uint32_t (*get_lines)(void *self); /* PSX_LINK_DSR/CTS */
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int (*connected)(void *self);
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void (*reset)(void *self);
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/* Snapshot: inbound ring + own output lines, due_cycle as delta vs `now`. */
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uint32_t (*snap_bytes)(void *self);
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void (*snap_write)(void *self, uint8_t *p, uint64_t now);
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int (*snap_read)(void *self, const uint8_t *p, uint32_t len,
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uint64_t now);
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} PsxLinkOps;
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typedef struct PsxLinkEndpoint {
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const PsxLinkOps *ops;
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void *self;
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} PsxLinkEndpoint;
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/* Ring depth per direction (fixed; overrun at the DEVICE FIFO, not here —
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* at real link rates the wire never holds more than one char in flight). */
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#define PSX_LINK_RING_DEPTH 64u
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/* No cable: DSR/CTS low, tx discarded, rx never yields. */
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PsxLinkEndpoint *psx_link_null(void);
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/* Self-wired test cable: TX -> own RX, DTR -> own DSR, RTS -> own CTS. */
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PsxLinkEndpoint *psx_link_loopback_create(void);
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void psx_link_loopback_destroy(PsxLinkEndpoint *ep);
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/* Crossover cable between two SIO1 devices:
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* A.TX -> B.RX, A.DTR -> B.DSR, A.RTS -> B.CTS (and mirrored). */
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void psx_link_crossover_create(PsxLinkEndpoint **a, PsxLinkEndpoint **b);
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void psx_link_crossover_destroy(PsxLinkEndpoint *a, PsxLinkEndpoint *b);
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/* Deterministic extra wire delay added to each character at tx(). */
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void psx_link_set_latency_cycles(PsxLinkEndpoint *ep, uint32_t cycles);
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#ifdef __cplusplus
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}
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#endif
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#endif /* PSX_LINK_H */
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