Cross-core handoff block backed by a fixed shared-SRAM address. More...

#include <lowpower_holdpage.h>

Data Fields
volatile uint32_t	magic
	M85 stamps k_lowpower_magic when ready.
volatile uint32_t	page_num
	Held page; M85 sets 0, M33 bumps on turn.
volatile uint32_t	active_core
	Which core owns the page (lowpower_const_t).
volatile uint32_t	m33_heartbeat
	M33 increments each hold-loop iteration.
volatile uint32_t	sw1_events
	M33 counts SW1 (page-turn) press edges.

Detailed Description

Cross-core handoff block backed by a fixed shared-SRAM address.

All fields are volatile so each core re-reads memory rather than caching a value in a register. The M85 owns magic and the initial page_num / active_core (writer); the M33 owns m33_heartbeat, sw1_events, and the post-handoff page_num (writer). The opposite core only reads what it does not own.

Invariant: magic is 0 until the M85 stamps k_lowpower_magic, then holds.; active_core is k_lowpower_core_m33 once the M85 has parked.; m33_heartbeat increases monotonically while the M33 holds.

Example:: volatile lowpower_mailbox_t* mb = lowpower_mailbox();

mb->page_num = 0U;

mb->active_core = (uint32_t)k_lowpower_core_m33;

mb->magic = (uint32_t)k_lowpower_magic;

__asm volatile("dsb" ::: "memory"); // publish before releasing the M33

lowpower_mailbox
static volatile lowpower_mailbox_t * lowpower_mailbox(void)
Typed pointer to the fixed-address shared mailbox.
Definition lowpower_holdpage.h:142

k_lowpower_magic
@ k_lowpower_magic
"HOLD" – M85 stamps it when ready.
Definition lowpower_holdpage.h:85

k_lowpower_core_m33
@ k_lowpower_core_m33
active_core: the M33 holds the page.
Definition lowpower_holdpage.h:87

lowpower_mailbox_t
Cross-core handoff block backed by a fixed shared-SRAM address.
Definition lowpower_holdpage.h:116

lowpower_mailbox_t::page_num
volatile uint32_t page_num
Held page; M85 sets 0, M33 bumps on turn.
Definition lowpower_holdpage.h:118

lowpower_mailbox_t::active_core
volatile uint32_t active_core
Which core owns the page (lowpower_const_t).
Definition lowpower_holdpage.h:119

lowpower_mailbox_t::magic
volatile uint32_t magic
M85 stamps k_lowpower_magic when ready.
Definition lowpower_holdpage.h:117

See also: lowpower_mailbox()

Since: 0.1.0

Definition at line 116 of file lowpower_holdpage.h.

Field Documentation

◆ active_core

volatile uint32_t lowpower_mailbox_t::active_core

Which core owns the page (lowpower_const_t).

Definition at line 119 of file lowpower_holdpage.h.

Referenced by render_page0().

◆ m33_heartbeat

volatile uint32_t lowpower_mailbox_t::m33_heartbeat

M33 increments each hold-loop iteration.

Definition at line 120 of file lowpower_holdpage.h.

Referenced by cpu1_hold_page(), park_low_power(), and render_page0().

◆ magic

volatile uint32_t lowpower_mailbox_t::magic

M85 stamps k_lowpower_magic when ready.

Definition at line 117 of file lowpower_holdpage.h.

Referenced by render_page0().

◆ page_num

volatile uint32_t lowpower_mailbox_t::page_num

Held page; M85 sets 0, M33 bumps on turn.

Definition at line 118 of file lowpower_holdpage.h.

Referenced by cpu1_hold_page(), and render_page0().

◆ sw1_events

volatile uint32_t lowpower_mailbox_t::sw1_events

M33 counts SW1 (page-turn) press edges.

Definition at line 121 of file lowpower_holdpage.h.