heartbeat.c File Reference

SPDX-License-Identifier: MIT. More...

#include "heartbeat.h"
#include <string.h>

Functions
static bool	elapsed_at_least (uint32_t now, uint32_t then, uint32_t ms)
	Every comparison is an unsigned difference against a timeout, never a comparison of two timestamps.
void	heartbeat_gen_init (heartbeat_gen_t *g)
	Start held low: nothing downstream may run until this loop asks for it.
bool	heartbeat_gen_step (heartbeat_gen_t *g, uint32_t now_ms, bool alive)
	Advance the generator; returns the level the pin should be driven to.
void	heartbeat_mon_init (heartbeat_mon_t *m)
	Start not alive, with no edge seen.
void	heartbeat_mon_edge (heartbeat_mon_t *m, uint32_t now_ms)
	Record an edge on the safety line.
bool	heartbeat_mon_alive (heartbeat_mon_t *m, uint32_t now_ms)
	Whether the line may be believed now.

Detailed Description

SPDX-License-Identifier: MIT.

Function Documentation

elapsed_at_least()

bool elapsed_at_least ( uint32_t now, uint32_t then, uint32_t ms )

inlinestatic

Every comparison is an unsigned difference against a timeout, never a comparison of two timestamps.

A 32-bit millisecond counter wraps after 49.7 days, and now < then is wrong for about 1ms either side of the wrap; the subtraction wraps with the counter and stays correct.

heartbeat_gen_init()

void heartbeat_gen_init

(

heartbeat_gen_t *

g

)

Start held low: nothing downstream may run until this loop asks for it.

Parameters

g	Generator state to initialise.

heartbeat_gen_step()

bool heartbeat_gen_step	(	heartbeat_gen_t *	g,
		uint32_t	now_ms,
		bool	alive )

Advance the generator; returns the level the pin should be driven to.

alive is the caller's own judgement of whether it is fit to keep the bench running – touch answering, link up, no latched stop. When it is false the line goes low immediately rather than merely stopping: waiting for the monostable to time out would spend its whole period still enabled, and the fastest correct thing to do with a stop is all of it at once.

Call it as often as you like; it edges no faster than HEARTBEAT_PERIOD_MS.

Parameters

g	Generator state.
now_ms	Current time, in milliseconds.
alive	true when the caller judges the bench fit to run.

Returns

The level the pin is driven to.

heartbeat_mon_alive()

bool heartbeat_mon_alive	(	heartbeat_mon_t *	m,
		uint32_t	now_ms )

Whether the line may be believed now.

Must be called even when no edges are arriving: silence is the failure this exists to catch, and silence generates no events. Calling it is what notices that nothing has happened.

Parameters

m	Monitor state.
now_ms	Current time, in milliseconds.

Returns

true when the line may be believed now.

heartbeat_mon_edge()

void heartbeat_mon_edge	(	heartbeat_mon_t *	m,
		uint32_t	now_ms )

Record an edge on the safety line.

Called from wherever edges are noticed – an interrupt, or a poll that samples faster than HEARTBEAT_MIN_GAP_MS. It only ever costs a subtraction and a compare, so an ISR is a fine place for it.

Parameters

m	Monitor state.
now_ms	Time of the edge, in milliseconds.

heartbeat_mon_init()

void heartbeat_mon_init

(

heartbeat_mon_t *

m

)

Start not alive, with no edge seen.

Parameters

m	Monitor state to initialise.