[fiber] Add cooperative, stackful fibers

repo.lb

@@ -274,6 +274,10 @@ def init(repo):
                      description=descr_target,
                      enumeration=devices))
 
+    # Invisible option guarding the Fiber API until it is ready
+    repo.add_option(BooleanOption(name="__fibers", default=False,
+                                  description="Enable unstable fiber API."))
+
 def prepare(repo, options):
     repo.add_modules_recursive("ext", modulefile="*.lb")
     repo.add_modules_recursive("src", modulefile="*.lb")

src/modm/architecture/utils.hpp

@@ -72,6 +72,9 @@
 	/// Marks a declaration as deprecated and displays a message.
 	#define modm_deprecated(msg)
 
+	/// Tells the compiler to not generate prologue/epilogue code for this function.
+	#define modm_naked
+
 	/// Places a function in the fastest executable memory:
 	/// instruction cache, core coupled memory or SRAM as fallback.
 	#define modm_fastcode
@@ -134,6 +137,7 @@
 	#define modm_fallthrough		__attribute__((fallthrough))
 	#define modm_noreturn			__attribute__((noreturn))
 	#define modm_warn_unused_result	__attribute__((warn_unused_result))
+	#define modm_naked				__attribute__((naked))
 
 	#ifdef MODM_COMPILER_MINGW
 	 	// FIXME: Windows Object Format PE does not support weak symbols

src/modm/processing/fiber.hpp

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2020, Erik Henriksson
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#include "fiber/fiber.hpp"
+#include "fiber/scheduler.hpp"

src/modm/processing/fiber/context.h

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2020, Erik Henriksson
+ * Copyright (c) 2021, Niklas Hauser
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#pragma once
+
+#include <stdint.h>
+#include <stddef.h>
+#include <modm/architecture/utils.hpp>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+struct modm_context_t
+{
+	uintptr_t sp;
+	size_t stack_size;
+};
+
+/// Prepares the stack to jump into function with arg and call end on return
+modm_context_t
+modm_context_init(uintptr_t stack, uintptr_t arg, uintptr_t fn, uintptr_t end);
+
+/// Switches control from the main context to the user context.
+void
+modm_context_start(uintptr_t sp);
+
+/// Jumps from the "from" user context to the "to" user context.
+void
+modm_context_jump(uintptr_t* from_sp, uintptr_t to_sp);
+
+/// Switches control back to the main context from the user context.
+void __attribute__((noreturn))
+modm_context_end();
+
+#ifdef __cplusplus
+}
+#endif

src/modm/processing/fiber/context_arm_m.cpp.in

@@ -0,0 +1,171 @@
+/*
+ * Copyright (c) 2020, Erik Henriksson
+ * Copyright (c) 2021, Niklas Hauser
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#include "context.h"
+
+/* Stack layout (growing downwards):
+ * Registers r4-r11 must be preserved across subroutine calls.
+ *
+ * LR
+%% if not cm0
+ * r11
+ * r10
+ * r9
+ * r8
+%% endif
+ * r7
+ * r6
+ * r5
+ * r4
+%% if cm0
+ * r11
+ * r10
+ * r9
+ * r8
+%% endif
+%% if with_fpu
+ * s31
+ * s30
+ * s29
+ * s28
+ * s27
+ * s26
+ * s25
+ * s24
+ * s23
+ * s22
+ * s21
+ * s20
+ * s19
+ * s18
+ * s17
+ * s16
+ *
+ * From the PCSAA:
+ * Registers s16-s31 (d8-d15, q4-q7) must be preserved across subroutine calls;
+ * registers s0-s15 (d0-d7, q0- q3) do not need to be preserved (and can be used
+ * for passing arguments or returning results in standard procedure-call
+ * variants). Registers d16-d31 (q8-q15), if present, do not need to be
+ * preserved.
+%% endif
+ */
+
+static void modm_naked
+modm_context_entry()
+{
+	asm volatile
+	(
+		"pop {r0}		\n\t"	// Loads return address
+		"mov lr, r0		\n\t"	// Set LR
+		"pop {r0, pc}	\n\t"	// Load argument and jump
+	);
+}
+
+modm_context_t
+modm_context_init(uintptr_t stack, uintptr_t arg, uintptr_t fn, uintptr_t end)
+{
+	uintptr_t* sp = (uintptr_t*)arg;
+	*--sp = fn;		// actual fiber function
+	*--sp = arg;	// r0 argument
+	*--sp = end;	// called after fn returns
+
+	*--sp = (uintptr_t) modm_context_entry;
+	sp -= 8{% if with_fpu %}+16{% endif %};		// r4-r11{% if with_fpu %}, s16-s31{% endif %}
+	return {(uintptr_t) sp, arg - stack};
+}
+
+#define MODM_PUSH_CONTEXT() \
+%% if cm0
+		"push {r4-r7, lr}		\n\t" \
+		"mov r4, r8				\n\t" \
+		"mov r5, r9				\n\t" \
+		"mov r6, r10			\n\t" \
+		"mov r7, r11			\n\t" \
+		"push {r4-r7}			\n\t"
+%% else
+		"push {r4-r11, lr}		\n\t"{% if with_fpu %} \
+		"vpush {d8-d15}			\n\t"{% endif %}
+%% endif
+%#
+#define MODM_POP_CONTEXT() \
+%% if cm0
+		"pop {r4-r7}			\n\t" \
+		"mov r8, r4				\n\t" \
+		"mov r9, r5				\n\t" \
+		"mov r10, r6			\n\t" \
+		"mov r11, r7			\n\t" \
+		"pop {r4-r7, pc}		\n\t"
+%% else
+%% if with_fpu
+		"vpop {d8-d15}			\n\t" \
+%% endif
+		"pop {r4-r11, pc}		\n\t"
+%% endif
+%#
+void modm_naked
+modm_context_start(uintptr_t)
+{
+	asm volatile
+	(
+		MODM_PUSH_CONTEXT()
+
+		"mrs r2, control		\n\t"
+%% if cm0
+		"mov r1, #2				\n\t"
+		"orr r2, r2, r1			\n\t"	// Set SPSEL
+%% else
+		"orr r2, r2, #2			\n\t"	// Set SPSEL
+%% endif
+		"msr control, r2		\n\t"
+
+		"mov sp, r0				\n\t"	// Set PSP to fiber stack (to.sp)
+
+		MODM_POP_CONTEXT()
+	);
+}
+
+void modm_naked
+modm_context_jump(uintptr_t*, uintptr_t)
+{
+	asm volatile
+	(
+		MODM_PUSH_CONTEXT()
+%#
+%% if cm0
+		"mov r2, sp				\n\t"
+		"str r2, [r0]			\n\t"	// Store the SP in "from"
+%% else
+		"str sp, [r0]			\n\t"	// Store the SP in "from"
+%% endif
+		"mov sp,  r1			\n\t"	// Restore SP from "to"
+
+		MODM_POP_CONTEXT()
+	);
+}
+
+void modm_naked
+modm_context_end()
+{
+	asm volatile
+	(
+		"mrs r0, control		\n\t"
+%% if cm0
+		"mov r1, #2				\n\t"
+		"bic r0, r0, r1			\n\t"	// Unset SPSEL
+%% else
+		"bic r0, r0, #2			\n\t"	// Unset SPSEL
+%% endif
+		"msr control, r0		\n\t"
+
+		MODM_POP_CONTEXT()
+	);
+}