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SEGGER_RTT_ASM_ARMv7M.S
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SEGGER_RTT_ASM_ARMv7M.S
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/*********************************************************************
* (c) SEGGER Microcontroller GmbH *
* The Embedded Experts *
* www.segger.com *
**********************************************************************
-------------------------- END-OF-HEADER -----------------------------
File : SEGGER_RTT_ASM_ARMv7M.S
Purpose : Assembler implementation of RTT functions for ARMv7M
Additional information:
This module is written to be assembler-independent and works with
GCC and clang (Embedded Studio) and IAR.
*/
#define SEGGER_RTT_ASM // Used to control processed input from header file
#include "SEGGER_RTT.h"
#if defined (RTT_USE_ASM) && (RTT_USE_ASM == 1)
/*********************************************************************
*
* Defines, fixed
*
**********************************************************************
*/
#define _CCIAR 0
#define _CCCLANG 1
#if (defined __SES_ARM) || (defined __GNUC__) || (defined __clang__)
#define _CC_TYPE _CCCLANG
#define _PUB_SYM .global
#define _EXT_SYM .extern
#define _END .end
#define _WEAK .weak
#define _THUMB_FUNC .thumb_func
#define _THUMB_CODE .code 16
#define _WORD .word
#define _SECTION(Sect, Type, AlignExp) .section Sect ##, "ax"
#define _ALIGN(Exp) .align Exp
#define _PLACE_LITS .ltorg
#define _DATA_SECT_START
#define _C_STARTUP _start
#define _STACK_END __stack_end__
#define _RAMFUNC
//
// .text => Link to flash
// .fast => Link to RAM
// OtherSect => Usually link to RAM
// Alignment is 2^x
//
#elif defined (__IASMARM__)
#define _CC_TYPE _CCIAR
#define _PUB_SYM PUBLIC
#define _EXT_SYM EXTERN
#define _END END
#define _WEAK _WEAK
#define _THUMB_FUNC
#define _THUMB_CODE THUMB
#define _WORD DCD
#define _SECTION(Sect, Type, AlignExp) SECTION Sect ## : ## Type ## :REORDER:NOROOT ## (AlignExp)
#define _ALIGN(Exp) alignrom Exp
#define _PLACE_LITS
#define _DATA_SECT_START DATA
#define _C_STARTUP __iar_program_start
#define _STACK_END sfe(CSTACK)
#define _RAMFUNC SECTION_TYPE SHT_PROGBITS, SHF_WRITE | SHF_EXECINSTR
//
// .text => Link to flash
// .textrw => Link to RAM
// OtherSect => Usually link to RAM
// NOROOT => Allows linker to throw away the function, if not referenced
// Alignment is 2^x
//
#endif
#if (_CC_TYPE == _CCIAR)
NAME SEGGER_RTT_ASM_ARMv7M
#else
.syntax unified
#endif
#define SHT_PROGBITS 0x1
/*********************************************************************
*
* Public / external symbols
*
**********************************************************************
*/
_EXT_SYM __aeabi_memcpy
_EXT_SYM __aeabi_memcpy4
_EXT_SYM _SEGGER_RTT
_PUB_SYM SEGGER_RTT_ASM_WriteSkipNoLock
/*********************************************************************
*
* SEGGER_RTT_WriteSkipNoLock
*
* Function description
* Stores a specified number of characters in SEGGER RTT
* control block which is then read by the host.
* SEGGER_RTT_WriteSkipNoLock does not lock the application and
* skips all data, if the data does not fit into the buffer.
*
* Parameters
* BufferIndex Index of "Up"-buffer to be used (e.g. 0 for "Terminal").
* pBuffer Pointer to character array. Does not need to point to a \0 terminated string.
* NumBytes Number of bytes to be stored in the SEGGER RTT control block.
* MUST be > 0!!!
* This is done for performance reasons, so no initial check has do be done.
*
* Return value
* 1: Data has been copied
* 0: No space, data has not been copied
*
* Notes
* (1) If there is not enough space in the "Up"-buffer, all data is dropped.
* (2) For performance reasons this function does not call Init()
* and may only be called after RTT has been initialized.
* Either by calling SEGGER_RTT_Init() or calling another RTT API function first.
*/
_SECTION(.text, CODE, 2)
_ALIGN(2)
_THUMB_FUNC
SEGGER_RTT_ASM_WriteSkipNoLock: // unsigned SEGGER_RTT_WriteSkipNoLock(unsigned BufferIndex, const void* pData, unsigned NumBytes) {
//
// Cases:
// 1) RdOff <= WrOff => Space until wrap-around is sufficient
// 2) RdOff <= WrOff => Space after wrap-around needed (copy in 2 chunks)
// 3) RdOff < WrOff => No space in buf
// 4) RdOff > WrOff => Space is sufficient
// 5) RdOff > WrOff => No space in buf
//
// 1) is the most common case for large buffers and assuming that J-Link reads the data fast enough
//
// Register usage:
// R0 Temporary needed as RdOff, <Tmp> register later on
// R1 pData
// R2 <NumBytes>
// R3 <Tmp> register. Hold free for subroutine calls
// R4 <Rem>
// R5 pRing->pBuffer
// R6 pRing (Points to active struct SEGGER_RTT_BUFFER_DOWN)
// R7 WrOff
//
PUSH {R4-R7}
ADD R3,R0,R0, LSL #+1
LDR.W R0,=_SEGGER_RTT // pRing = &_SEGGER_RTT.aUp[BufferIndex];
ADD R0,R0,R3, LSL #+3
ADD R6,R0,#+24
LDR R0,[R6, #+16] // RdOff = pRing->RdOff;
LDR R7,[R6, #+12] // WrOff = pRing->WrOff;
LDR R5,[R6, #+4] // pRing->pBuffer
CMP R7,R0
BCC.N _CheckCase4 // if (RdOff <= WrOff) { => Case 1), 2) or 3)
//
// Handling for case 1, later on identical to case 4
//
LDR R3,[R6, #+8] // Avail = pRing->SizeOfBuffer - WrOff - 1u; => Space until wrap-around (assume 1 byte not usable for case that RdOff == 0)
SUBS R4,R3,R7 // <Rem> (Used in case we jump into case 2 afterwards)
SUBS R3,R4,#+1 // <Avail>
CMP R3,R2
BCC.N _CheckCase2 // if (Avail >= NumBytes) { => Case 1)?
_Case4:
ADDS R5,R7,R5 // pBuffer += WrOff
ADDS R0,R2,R7 // v = WrOff + NumBytes
//
// 2x unrolling for the copy loop that is used most of the time
// This is a special optimization for small SystemView packets and makes them even faster
//
_ALIGN(2)
_LoopCopyStraight: // memcpy(pRing->pBuffer + WrOff, pData, NumBytes);
LDRB R3,[R1], #+1
STRB R3,[R5], #+1 // *pDest++ = *pSrc++
SUBS R2,R2,#+1
BEQ _CSDone
LDRB R3,[R1], #+1
STRB R3,[R5], #+1 // *pDest++ = *pSrc++
SUBS R2,R2,#+1
BNE _LoopCopyStraight
_CSDone:
STR R0,[R6, #+12] // pRing->WrOff = WrOff + NumBytes;
MOVS R0,#+1
POP {R4-R7}
BX LR // Return 1
_CheckCase2:
ADDS R0,R0,R3 // Avail += RdOff; => Space incl. wrap-around
CMP R0,R2
BCC.N _Case3 // if (Avail >= NumBytes) { => Case 2? => If not, we have case 3) (does not fit)
//
// Handling for case 2
//
ADDS R0,R7,R5 // v = pRing->pBuffer + WrOff => Do not change pRing->pBuffer here because 2nd chunk needs org. value
SUBS R2,R2,R4 // NumBytes -= Rem; (Rem = pRing->SizeOfBuffer - WrOff; => Space until end of buffer)
_LoopCopyBeforeWrapAround: // memcpy(pRing->pBuffer + WrOff, pData, Rem); => Copy 1st chunk
LDRB R3,[R1], #+1
STRB R3,[R0], #+1 // *pDest++ = *pSrc++
SUBS R4,R4,#+1
BNE _LoopCopyBeforeWrapAround
//
// Special case: First check that assumed RdOff == 0 calculated that last element before wrap-around could not be used
// But 2nd check (considering space until wrap-around and until RdOff) revealed that RdOff is not 0, so we can use the last element
// In this case, we may use a copy straight until buffer end anyway without needing to copy 2 chunks
// Therefore, check if 2nd memcpy is necessary at all
//
ADDS R4,R2,#+0 // Save <NumBytes> (needed as counter in loop but must be written to <WrOff> after the loop). Also use this inst to update the flags to skip 2nd loop if possible
BEQ.N _No2ChunkNeeded // if (NumBytes) {
_LoopCopyAfterWrapAround: // memcpy(pRing->pBuffer, pData + Rem, NumBytes);
LDRB R3,[R1], #+1 // pData already points to the next src byte due to copy loop increment before this loop
STRB R3,[R5], #+1 // *pDest++ = *pSrc++
SUBS R2,R2,#+1
BNE _LoopCopyAfterWrapAround
_No2ChunkNeeded:
STR R4,[R6, #+12] // pRing->WrOff = NumBytes; => Must be written after copying data because J-Link may read control block asynchronously while writing into buffer
MOVS R0,#+1
POP {R4-R7}
BX LR // Return 1
_CheckCase4:
SUBS R0,R0,R7
SUBS R0,R0,#+1 // Avail = RdOff - WrOff - 1u;
CMP R0,R2
BCS.N _Case4 // if (Avail >= NumBytes) { => Case 4) == 1) ? => If not, we have case 5) == 3) (does not fit)
_Case3:
MOVS R0,#+0
POP {R4-R7}
BX LR // Return 0
_PLACE_LITS
_END
#endif // defined (RTT_USE_ASM) && (RTT_USE_ASM == 1)
/*************************** End of file ****************************/