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
r0	Argument, result, scratch register 1	Scratch
r1	Argument, result, scratch register 2	Scratch
r2	Argument, scratch register 3	Scratch
r3	Argument, scratch register 4	Scratch
r12	Intra-procedure-call scratch register	unused
r14	Link register (LR)	Link register (LR)
r9	Platform register (usage defined by platform in use)	unused
r15	Program counter (PC)	Program counter (PC)
r13	Stack pointer (SP)	Stack pointer (SP)
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
r10	Variable register 7	unused
r11	Variable register 8	unused

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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