+++ /dev/null
--*- Text -*-
-
-This document describes the proposed ABI for the D30V processor. This is
-revision 2 of the document.
-
-Revision history:
-
-Revision 1:
- Original revision of this document.
-
-Revision 2:
- Done after consultation with Mitsubshi about the calling sequence.
- This revision now reduces the number of registers the compiler will not
- touch from 18 registers down to 8.
-
- Register 1 is now a normal temporary register, since mvfacc rx,ay,32 is
- legal.
-
- Arguments greater than 4 bytes must be passed in an even register or at
- a double word alignment.
-
- The va_list type is a structure, not a char *.
-
- The stack must be aligned to 8 byte boundary. Doubles and long longs
- must also be aligned to 8 byte boundaries.
-
- System calls are specified via trap 31.
-
-Revision 3:
- I added discussion about compiler switches.
-
-Register usage:
-===============
-
- Registers Call Status Usage
- --------- ----------- -----
- R0 hardware Hardwired to 0
- R1 volatile temp
- R2 volatile Arg 1 and main return value.
- R3 volatile Arg 2 and low bits of 64 bit returns
- R4 - R17 volatile Args 3-16
- R18 volatile Static chain if used
- R19 - R25 volatile temps
- R26 - R33 saved Reserved for user use
- R34 - R60 saved Registers preserved across calls
- R61 saved Frame pointer if needed.
- R62 saved Return address pointer (hardware)
- R63 saved Stack pointer
- CR0 - CR3 hardware {normal,backup} {psw,pc}
- CR4 - CR6 hardware Reserved for future use
- CR7 - CR9 volatile Repeat count, addresses
- CR10 - CR11 saved Modulo start/end
- CR12 - CR14 hardware Reserved for future use
- CR15 - CR17 hardware Interrupt support
- F0 - F1 volatile Execution flags
- F2 - F3 volatile General flags
- F4 - F7 volatile Special purpose flags
- A0 volatile Accumulator
- A1 saved Accumulator
-
-Notes on the register usage:
-============================
-
- 1) R61 will hold the frame pointer if it is needed. Normally the frame
- pointer will not be needed, in which case this will become another
- saved register.
-
- 2) Repeat instructions and delayed branches cannot cross call boundaries.
- Similarly, all flags are assumed to not be preserved across calls.
-
- 3) Since so many registers are available, I reserved 8 registers (r26-r33)
- for the user to use for any purpose (global variables, interrupt
- routines, thread pointer, etc.). These registers will not be used by
- the compiler for any purpose.
-
- 4) One of the two accumulators is saved across calls.
-
- 5) Doubles and long longs will only be allocated to even/odd register
- pairs to allow use of the ld2w/st2w instructions.
-
-Miscellaneous call information:
-===============================
-
- 1) Structures are passed in registers, rounding them up to word
- boundaries.
-
- 2) Any argument that is greater than word size (4 bytes) must be aligned
- to a double word boundary and/or start in an even register. The
- intention here is to be able to use the ld2w/st2w instructions for
- moving doubles and long longs.
-
- 3) Variable argument functions are called with the same calling sequence
- as non-variable argument functions. When called, a variable argument
- function first saves the 16 registers (R2 - R17) used for passing
- arguments. The va_list type is a structure. The first element of the
- structure is a pointer to the first word saved on the stack, and the
- second element is a number that gives which argument number is being
- processed.
-
- 4) Word and double word sized structures/unions are returned in registers,
- other functions returning structures expect a temporary area address to
- be passed as the first argument.
-
-
-The stack frame when a function is called looks like:
-
-high | .... |
- +-------------------------------+
- | Argument word #20 |
- +-------------------------------+
- | Argument word #19 |
- +-------------------------------+
- | Argument word #18 |
- +-------------------------------+
- | Argument word #17 |
-low SP----> +-------------------------------+
-
-After the prologue is executed, the stack frame will look like:
-
-high | .... |
- +-------------------------------+
- | Argument word #20 |
- +-------------------------------+
- | Argument word #19 |
- +-------------------------------+
- | Argument word #18 |
- +-------------------------------+
- | Argument word #17 |
- Prev sp +-------------------------------+
- | |
- | Save for arguments 1..16 if |
- | the func. uses stdarg/varargs |
- | |
- +-------------------------------+
- | |
- | Save area for preserved regs |
- | |
- +-------------------------------+
- | |
- | Local variables |
- | |
- +-------------------------------+
- | |
- | alloca space if used |
- | |
- +-------------------------------+
- | |
- | Space for outgoing arguments |
- | |
-low SP----> +-------------------------------+
-
-System Calls
-============
-
-System calls will be done using "TRAP 31". Input arguments will be in R2 - R5,
-and the system call number will be in R6. Return values from the system call
-will be in R2. Negative values of the return indicate the system call failed,
-and the value is the negative of the error code. Here are the assigned system
-call numbers (value in R6):
-
- exit 1
- open 2
- close 3
- read 4
- write 5
- lseek 6
- unlink 7
- getpid 8
- kill 9
- fstat 10
- (11 is reserved for sbrk)
- argvlen 12
- argv 13
- chdir 14
- stat 15
- chmod 16
- utime 17
- time 18
-
-Compiler Switches
-=================
-
-The following d30v specific compiler switches are currently supported:
-
- -mextmem Link .text/.data/.bss/etc in external memory.
-
- -mextmemory Same as -mextmem.
-
- -monchip Link .text/.data/.bss/etc in the onchip data/text
- memory.
-
- -mno-asm-optimize Do not pass -O to the assembler when optimizing (the -O
- switch will mark two short instructions that don't
- interfere with each other as being done parallel
- instead of sequentially).
-
- -masm-optimize [default] If optimizing, pass -O to the assembler.
-
- -mbranch-cost=n Increase the internal costs of branches to n. Higher
- costs means that the compiler will issue more
- instructions to avoid doing a branch. The default is
- 2.
-
- -mcond-exec=n Replace branches around n insns with conditional
- execution if we can. Default is 4.
-
-
-Sections
-========
-
-You can override the effect of the -mextmem/-monchip options by putting
-functions into either the ".stext" or ".etext" sections. If you put them into
-the ".stext" section, the linker will always link the function into the onchip
-memory area. Similarly, if you put the function in the ".etext" section, the
-linker will always link the function into the external memory area.
-
-Data can be controlled as well. If you put the data in the ".sdata" section,
-the linker will put the data into the onchip data area. Similarly, if you put
-the data in the ".edata" section, the linker will put the data into the
-external memory.
-
-
-Stack pointer
-=============
-
-The crt0.o that we ship loads up the stack pointer with the value of the label
-__stack. If you do not define a value for __stack, the linker will choose the
-top of the onchip data area (0x20008000) for the stack pointer. You can set a
-new value via the options:
-
- -Wl,-defsym,__stack=0x20008000
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