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## [/] [amber/] [trunk/] [sw/] [mini-libc/] [**libc_asm.S**] - Rev 81

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`/*----------------------------------------------------------------`

`// //`

`// libc_asm.S //`

`// //`

`// This file is part of the Amber project //`

`// http://www.opencores.org/project,amber //`

`// //`

`// Description //`

`// Assembly routines for the mini-libc library. //`

`// //`

`// Author(s): //`

`// - Conor Santifort, csantifort.amber@gmail.com //`

`// //`

`//////////////////////////////////////////////////////////////////`

`// //`

`// Copyright (C) 2010 Authors and OPENCORES.ORG //`

`// //`

`// This source file may be used and distributed without //`

`// restriction provided that this copyright statement is not //`

`// removed from the file and that any derivative work contains //`

`// the original copyright notice and the associated disclaimer. //`

`// //`

`// This source file is free software; you can redistribute it //`

`// and/or modify it under the terms of the GNU Lesser General //`

`// Public License as published by the Free Software Foundation; //`

`// either version 2.1 of the License, or (at your option) any //`

`// later version. //`

`// //`

`// This source is distributed in the hope that it will be //`

`// useful, but WITHOUT ANY WARRANTY; without even the implied //`

`// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR //`

`// PURPOSE. See the GNU Lesser General Public License for more //`

`// details. //`

`// //`

`// You should have received a copy of the GNU Lesser General //`

`// Public License along with this source; if not, download it //`

`// from http://www.opencores.org/lgpl.shtml //`

`// //`

`----------------------------------------------------------------*/`

`#include "amber_registers.h"`

`/* _testfail: Used to terminate execution in Verilog simulations */`

`/* On the board just puts the processor into an infinite loop */`

`.section .text`

`.globl _testfail`

`_testfail:`

`ldr r11, AdrTestStatus`

`str r0, [r11]`

`b _testfail`

`/* _testpass: Used to terminate execution in Verilog simulations */`

`/* On the board just puts the processor into an infinite loop */`

`.globl _testpass`

`_testpass:`

`ldr r11, AdrTestStatus`

`mov r10, #17`

`str r10, [r11]`

`b _testpass`

`/* _outbyte: Output a single character through UART 0 */`

`@ if the uart tx fifo is stuck full`

`@ this routine will cycle forever`

`.globl _outbyte`

`_outbyte:`

`ldr r1, AdrUARTDR`

`ldr r3, AdrUARTFR`

`@ Check the tx_full flag`

`1: ldr r2, [r3]`

`and r2, r2, #0x20`

`cmp r2, #0`

`streqb r0, [r1]`

`moveqs pc, lr @ return`

`bne 1b`

`/* _inbyte: Input a single character from UART 0 */`

`@ r0 is the timeout in mS`

`.globl _inbyte`

`_inbyte:`

`ldr r2, AdrUARTDR @ data`

`ldr r3, AdrUARTFR @ flags`

`@ Multiple delay value by 2560`

`@ as the delay loop takes about 12 clock cycles running cached`

`@ so that factor gives 1:1mS @33MHz`

`mov r1, r0, lsl #11`

`add r1, r1, r0, lsl #9`

`@ Check the r2 empty flag`

`2: ldr r0, [r3]`

`ands r0, r0, #0x10`

`ldreqb r0, [r2]`

`moveq pc, lr`

`@ decrement timeout`

`subs r1, r1, #1`

`bne 2b`

`mov r0, #-1`

`movs pc, lr`

`/* _div: Integer division function */`

`@ Divide r0 by r1`

`@ Answer returned in r1`

`.globl _div`

`.globl __aeabi_idiv`

`__aeabi_idiv:`

`_div:`

`stmdb sp!, {r4, lr}`

`@ set r4 to 1 if one of the two inputs is negative`

`and r2, r0, #0x80000000`

`and r3, r1, #0x80000000`

`eor r4, r2, r3`

`@ Invert negative numbers`

`tst r0, #0x80000000`

`mvnne r0, r0`

`addne r0, r0, #1`

`tst r1, #0x80000000`

`mvnne r1, r1`

`addne r1, r1, #1`

`@ divide r1 by r2, also use registers r0 and r4`

`mov r2, r1`

`mov r1, r0`

`cmp r2, #0`

`beq 3f`

`@ In order to divide r1 by r2, the first thing we need to do is to shift r2`

`@ left by the necessary number of places. The easiest method of doing this`

`@ is simply by trial and error - shift until we discover that r2 has become`

`@ too big, then stop.`

`mov r0,#0 @ clear r0 to accumulate result`

`mov r3,#1 @ set bit 0 in r3, which will be`

`@ shifted left then right`

`1: cmp r3, #0 @ escape on error`

`moveq r3, #0x10000000`

`beq 2f`

`cmp r2,r1`

`movls r2,r2,lsl#1`

`movls r3,r3,lsl#1`

`bls 1b`

`@ shift r2 left until it is about to be bigger than r1`

`@ shift r3 left in parallel in order to flag how far we have to go`

`@ r0 will be used to hold the result. The role of r3 is more complicated.`

`@ In effect, we are using r3 to mark where the right-hand end of r2 has got to`

`@ - if we shift r2 three places left, this will be indicated by a value of %1000`

`@ in r3. However, we also add it to r0 every time we manage a successful subtraction,`

`@ since it marks the position of the digit currently being calculated in the answer.`

`@ so at the time of the first subtraction, r3 would have been %100, at the time`

`@ of the second (which failed) it would have been %10, and at the time of the`

`@ third %1. Adding it to r0 after each successful subtraction would have`

`@ given us, once again, the answer of %101!`

`@ Now for the loop that actually does the work:`

`2: cmp r1,r2 @ carry set if r1>r2 (don't ask why)`

`subcs r1,r1,r2 @ subtract r2 from r1 if this would`

`@ give a positive answer`

`addcs r0,r0,r3 @ and add the current bit in r3 to`

`@ the accumulating answer in r0`

`@ In subtraction (a cmp instruction simulates a subtraction in`

`@ order to set the flags), if r1 - r2 gives a positive answer and no 'borrow'`

`@ is required, the carry flag is set. This is required in order to make SBC`

`@ (Subtract with Carry) work properly when used to carry out a 64-bit subtraction,`

`@ but it is confusing!`

`@ In this case, we are turning it to our advantage. The carry flag is set to`

`@ indicate that a successful subtraction is possible, i.e. one that doesn't`

`@ generate a negative result, and the two following instructions are carried`

`@ out only when the condition Carry Set applies. Note that the 'S' on the end`

`@ of these instructions is part of the 'CS' condition code and does not mean`

`@ that they set the flags!`

`movs r3,r3,lsr #1 @ Shift r3 right into carry flag`

`movcc r2,r2,lsr #1 @ and if bit 0 of r3 was zero, also`

`@ shift r2 right`

`bcc 2b @ If carry not clear, r3 has shifted`

`@ back to where it started, and we`

`@ can end`

`@ if one of the inputs is negetive then return a negative result`

`tst r4, #0x80000000`

`mvnne r0, r0`

`addne r0, r0, #1`

`3: ldmia sp!, {r4, pc}^`

`/* strcpy: String copy function`

`char * strcpy ( char * destination, const char * source );`

`destination is returned`

`*/`

`@ r0 points to destination`

`@ r1 points to source string which terminates with a 0`

`.globl strcpy`

`strcpy:`

`stmdb sp!, {r4-r6, lr}`

`@ Use r6 to process the destination pointer.`

`@ At the end of the function, r0 is returned, so need to preserve it`

`mov r6, r0`

`@ only if both strings are zero-aligned use the fast 'aligned' algorithm`

`orr r2, r6, r1`

`tst r2, #3`

`bne strcpy_slow`

`strcpy_fast:`

`@ process strings 12 bytes at a time`

`ldmia r1!, {r2-r5}`

`@ check for a zero byte`

`@ only need to examine one of the strings because`

`@ they are equal up to this point!`

`tst r2, #0xff`

`tstne r2, #0xff00`

`tstne r2, #0xff0000`

`tstne r2, #0xff000000`

`strne r2, [r6], #4`

`subeq r1, r1, #4`

`tstne r3, #0xff`

`tstne r3, #0xff00`

`tstne r3, #0xff0000`

`tstne r3, #0xff000000`

`strne r3, [r6], #4`

`subeq r1, r1, #4`

`tstne r4, #0xff`

`tstne r4, #0xff00`

`tstne r4, #0xff0000`

`tstne r4, #0xff000000`

`strne r4, [r6], #4`

`subeq r1, r1, #4`

`tstne r5, #0xff`

`tstne r5, #0xff00`

`tstne r5, #0xff0000`

`tstne r5, #0xff000000`

`strne r5, [r6], #4`

`subeq r1, r1, #4`

`@ loop back to look at next 12 bytes`

`bne strcpy_fast`

`@ the source string contains a zero character`

`strcpy_aligned_slow:`

`@ unroll the loop 4 times`

`ldr r3, [r1], #4`

`strb r3, [r6], #1`

`ands r4, r3, #0xff`

`ldmeqia sp!, {r4-r6, pc}^`

`lsr r3, r3, #8`

`strb r3, [r6], #1`

`ands r4, r3, #0xff`

`ldmeqia sp!, {r4-r6, pc}^`

`lsr r3, r3, #8`

`strb r3, [r6], #1`

`ands r4, r3, #0xff`

`ldmeqia sp!, {r4-r6, pc}^`

`lsr r3, r3, #8`

`strb r3, [r6], #1`

`ands r4, r3, #0xff`

`ldmeqia sp!, {r4-r6, pc}^`

`b strcpy_aligned_slow`

`strcpy_slow:`

`@ unroll the loop 4 times`

`ldrb r3, [r1], #1`

`strb r3, [r6], #1`

`cmp r3, #0`

`ldmeqia sp!, {r4-r6, pc}^`

`ldrb r3, [r1], #1`

`strb r3, [r6], #1`

`cmp r3, #0`

`ldmeqia sp!, {r4-r6, pc}^`

`ldrb r3, [r1], #1`

`strb r3, [r6], #1`

`cmp r3, #0`

`ldmeqia sp!, {r4-r6, pc}^`

`ldrb r3, [r1], #1`

`strb r3, [r6], #1`

`cmp r3, #0`

`ldmeqia sp!, {r4-r6, pc}^`

`b strcpy_slow`

`/* int strcmp ( const char * str1, const char * str2 );`

`A value greater than zero indicates that the first character`

`that does not match has a greater value in str1 than in str2;`

`And a value less than zero indicates the opposite.`

`*/`

`.globl strcmp`

`strcmp:`

`stmdb sp!, {r4-r8, lr}`

`@ only if both strings are zero-aligned use the fast 'aligned' algorithm`

`orr r2, r0, r1`

`tst r2, #3`

`bne strcmp_slow`

`strcmp_fast:`

`@ process strings 12 bytes at a time`

`ldmia r0!, {r2-r4}`

`ldmia r1!, {r5-r7}`

`cmp r2, r5`

`bne 1f`

`cmpeq r3, r6`

`bne 2f`

`cmpeq r4, r7`

`bne 3f`

`@ strings are equal - find a zero byte`

`@ only need to examine one of the strings because`

`@ they are equal up to this point!`

`tst r2, #0xff`

`tstne r2, #0xff00`

`tstne r2, #0xff0000`

`tstne r2, #0xff000000`

`tstne r3, #0xff`

`tstne r3, #0xff00`

`tstne r3, #0xff0000`

`tstne r3, #0xff000000`

`tstne r4, #0xff`

`tstne r4, #0xff00`

`tstne r4, #0xff0000`

`tstne r4, #0xff000000`

`@ loop back to look at next 12 bytes`

`bne strcmp_fast`

`@ the first string contains a zero character`

`@ the strings are the same, so both strings end`

`moveq r0, #0`

`ldmeqia sp!, {r4-r8, pc}^`

`@ Roll back the string pointers to before the mismatch`

`@ then handle the remaining part byte by byte`

`1: sub r0, r0, #12`

`sub r1, r1, #12`

`strcmp_slow:`

`ldrb r2, [r0], #1`

`ldrb r3, [r1], #1`

`eors r4, r2, r3 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r5, [r0], #1`

`ldrb r6, [r1], #1`

`cmp r2, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r7, r5, r6 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r2, [r0], #1`

`ldrb r3, [r1], #1`

`cmp r5, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r4, r2, r3 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r5, [r0], #1`

`ldrb r6, [r1], #1`

`cmp r2, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r7, r5, r6 @ are the bytes equal ?`

`bne bytes_different`

`cmp r5, #0 @ are they equal and zero ?`

`beq bytes_zero`

`bne strcmp_slow`

`@ Skipping first 4 bytes so just check they`

`@ don't contain an end of string 0 character`

`2: tst r2, #0xff`

`tstne r2, #0xff00`

`tstne r2, #0xff0000`

`tstne r2, #0xff000000`

`beq bytes_zero`

`@ start looking at 5th byte`

`sub r0, r0, #8`

`sub r1, r1, #8`

`ldrb r2, [r0], #1`

`ldrb r3, [r1], #1`

`eors r4, r2, r3 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r5, [r0], #1`

`ldrb r6, [r1], #1`

`cmp r2, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r7, r5, r6 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r2, [r0], #1`

`ldrb r3, [r1], #1`

`cmp r5, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r4, r2, r3 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r5, [r0], #1`

`ldrb r6, [r1], #1`

`cmp r2, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r7, r5, r6 @ are the bytes equal ?`

`bne bytes_different`

`cmp r5, #0 @ are they equal and zero ?`

`beq bytes_zero`

`bne strcmp_slow`

`@ Skipping first 8 bytes so just check they`

`@ don't contain an end of string 0 character`

`3: tst r2, #0xff`

`tstne r2, #0xff00`

`tstne r2, #0xff0000`

`tstne r2, #0xff000000`

`tstne r3, #0xff`

`tstne r3, #0xff00`

`tstne r3, #0xff0000`

`tstne r3, #0xff000000`

`beq bytes_zero`

`sub r0, r0, #4`

`sub r1, r1, #4`

`ldrb r2, [r0], #1`

`ldrb r3, [r1], #1`

`eors r4, r2, r3 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r5, [r0], #1`

`ldrb r6, [r1], #1`

`cmp r2, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r7, r5, r6 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r2, [r0], #1`

`ldrb r3, [r1], #1`

`cmp r5, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r4, r2, r3 @ are the bytes equal ?`

`bne bytes_different`

`ldrb r5, [r0], #1`

`ldrb r6, [r1], #1`

`cmp r2, #0 @ are they equal and zero ?`

`beq bytes_zero`

`eors r7, r5, r6 @ are the bytes equal ?`

`bne bytes_different`

`cmp r5, #0 @ are they equal and zero ?`

`beq bytes_zero`

`bne strcmp_slow`

`bytes_zero:`

`moveq r0, #0 @ if equal and zero, return zero`

`ldmeqia sp!, {r4-r8, pc}^`

`bytes_different:`

`sub r0, r5, r6`

`ldmia sp!, {r4-r8, pc}^`

`@ initialize malloc`

`.globl init_malloc`

`init_malloc:`

`ldr r1, AdrMalloc`

`str r1, [r1]`

`mov pc, lr`

`/* void *malloc(size_t size); */`

`.globl malloc`

`malloc:`

`ldr r1, AdrMalloc`

`ldr r0, [r1]`

`add r0, r0, #0x10000`

`str r0, [r1]`

`mov pc, lr`

`/* strncpy: String copy function */`

`@ r0 points to destination`

`@ r1 points to source string`

`@ r2 is the number of bytes to copy`

`.globl strncpy`

`strncpy:`

`stmdb sp!, {r4, lr}`

`cmp r2, #0`

`beq 2f`

`add r4, r0, r2 @ set r4 to the address of the last byte copied`

`1: ldrb r3, [r1], #1`

`strb r3, [r0], #1`

`cmp r0, r4`

`bne 1b`

`2: ldmia sp!, {r4, pc}^`

`/* strncpy: String compare function */`

`@ return the difference if the strings don't match`

`.globl strncmp`

`strncmp:`

`stmdb sp!, {r4, r5, r6, lr}`

`@ check for 0 length`

`cmp r2, #0`

`moveq r0, #1`

`beq 2f`

`mov r3, #0`

`1: add r3, r3, #1`

`ldrb r4, [r0], #1`

`ldrb r5, [r1], #1`

`subs r6, r4, r5`

`movne r0, r6`

`bne 2f`

`cmp r3, r2`

`moveq r0, #0`

`beq 2f`

`b 1b`

`2: ldmia sp!, {r4, r5, r6, pc}^`

`AdrMalloc: .word 0x7000000`

`AdrTestStatus: .word ADR_AMBER_TEST_STATUS`

`AdrUARTDR: .word ADR_AMBER_UART0_DR`

`AdrUARTFR: .word ADR_AMBER_UART0_FR`

`/* ========================================================================= */`

`/* ========================================================================= */`

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