Calling C Functions from Forth and Vice Versa

Register Usage

Procedure Call Standard for the ARM Architecture AAPCS

https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/on-the-aapcs-with-an-application-to-efficient-parameter-passing

Register	AAPCS Purpose	MECRISP Forth Purpose	ISR Stacking
xPSR	Processor Status Register, Flags	Flags	1
r0	Argument, result, scratch register 1	Scratch	2
r1	Argument, result, scratch register 2	Scratch	3
r2	Argument, scratch register 3	Scratch	4
r3	Argument, scratch register 4	Scratch	5
r4	Variable register 1	DO Index
r5	Variable register 2	DO Limit
r6	Variable register 3	Top Of Stack TOS
r7	Variable register 4	Data stack pointer
r8	Variable register 5	unused
r9	Platform register (usage defined by platform in use)	unused
r10	Variable register 7	unused
r11	Variable register 8	unused
r12	Intra-procedure-call scratch register	unused	6
r13	Stack pointer (SP)	Stack pointer (SP)
r14	Link register (LR)	Link register (LR)	7
r15	Program counter (PC)	Program counter (PC)	0

VFP Register Usage

The VFP-v2 co-processor has 32 single-precision registers, s0-s31, which may also be accessed as 16 double-precision registers, d0-d15 (with d0 overlapping s0, s1; d1 overlapping s2, s3; etc).

Calling C Functions from Forth

Calling Forth Words from C Functions

Stack Pointer and Top Of Stack

-- Peter Schmid - 2020-07-13

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