Ankit Patel / Mbed 2 deprecated Robot_Control_UDP_Ethernet

Control a robot over the internet using UDP and a Ethernet interface.

Dependencies:   EthernetInterface Motor TextLCD mbed-rtos mbed Socket lwip-eth lwip-sys lwip

EthernetInterface/lwip-sys/arch/checksum.c@0:1496281373a5, 2013-10-17 (annotated)

Committer:
apatel336
Date:
Thu Oct 17 13:26:38 2013 +0000
Revision:
0:1496281373a5
Initial Release

Who changed what in which revision?

UserRevisionLine numberNew contents of line
apatel336 0:1496281373a5 1 /* Copyright (C) 2013 - Adam Green (https://github.com/adamgreen)
apatel336 0:1496281373a5 2
apatel336 0:1496281373a5 3 Licensed under the Apache License, Version 2.0 (the "License");
apatel336 0:1496281373a5 4 you may not use this file except in compliance with the License.
apatel336 0:1496281373a5 5 You may obtain a copy of the License at
apatel336 0:1496281373a5 6
apatel336 0:1496281373a5 7 http://www.apache.org/licenses/LICENSE-2.0
apatel336 0:1496281373a5 8
apatel336 0:1496281373a5 9 Unless required by applicable law or agreed to in writing, software
apatel336 0:1496281373a5 10 distributed under the License is distributed on an "AS IS" BASIS,
apatel336 0:1496281373a5 11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
apatel336 0:1496281373a5 12 See the License for the specific language governing permissions and
apatel336 0:1496281373a5 13 limitations under the License.
apatel336 0:1496281373a5 14 */
apatel336 0:1496281373a5 15 #if defined(TOOLCHAIN_GCC) && defined(__thumb2__)
apatel336 0:1496281373a5 16
apatel336 0:1496281373a5 17
apatel336 0:1496281373a5 18 /* This is a hand written Thumb-2 assembly language version of the
apatel336 0:1496281373a5 19 algorithm 3 version of lwip_standard_chksum in lwIP's inet_chksum.c. It
apatel336 0:1496281373a5 20 performs the checksumming 32-bits at a time and even unrolls the loop to
apatel336 0:1496281373a5 21 perform two of these 32-bit adds per loop iteration.
apatel336 0:1496281373a5 22
apatel336 0:1496281373a5 23 Returns:
apatel336 0:1496281373a5 24 16-bit 1's complement summation (not inversed).
apatel336 0:1496281373a5 25
apatel336 0:1496281373a5 26 NOTE: This function does return a uint16_t from the assembly language code
apatel336 0:1496281373a5 27 but is marked as void so that GCC doesn't issue warning because it
apatel336 0:1496281373a5 28 doesn't know about this low level return.
apatel336 0:1496281373a5 29 */
apatel336 0:1496281373a5 30 __attribute__((naked)) void /*uint16_t*/ thumb2_checksum(const void* pData, int length)
apatel336 0:1496281373a5 31 {
apatel336 0:1496281373a5 32 __asm (
apatel336 0:1496281373a5 33 ".syntax unified\n"
apatel336 0:1496281373a5 34 ".thumb\n"
apatel336 0:1496281373a5 35
apatel336 0:1496281373a5 36 // Push non-volatile registers we use on stack. Push link register too to
apatel336 0:1496281373a5 37 // keep stack 8-byte aligned and allow single pop to restore and return.
apatel336 0:1496281373a5 38 " push {r4, lr}\n"
apatel336 0:1496281373a5 39 // Initialize sum, r2, to 0.
apatel336 0:1496281373a5 40 " movs r2, #0\n"
apatel336 0:1496281373a5 41 // Remember whether pData was at odd address in r3. This is used later to
apatel336 0:1496281373a5 42 // know if it needs to swap the result since the summation will be done at
apatel336 0:1496281373a5 43 // an offset of 1, rather than 0.
apatel336 0:1496281373a5 44 " ands r3, r0, #1\n"
apatel336 0:1496281373a5 45 // Need to 2-byte align? If not skip ahead.
apatel336 0:1496281373a5 46 " beq 1$\n"
apatel336 0:1496281373a5 47 // We can return if there are no bytes to sum.
apatel336 0:1496281373a5 48 " cbz r1, 9$\n"
apatel336 0:1496281373a5 49
apatel336 0:1496281373a5 50 // 2-byte align.
apatel336 0:1496281373a5 51 // Place the first data byte in odd summation location since it needs to be
apatel336 0:1496281373a5 52 // swapped later. It's ok to overwrite r2 here as it only had a value of 0
apatel336 0:1496281373a5 53 // up until now. Advance r0 pointer and decrement r1 length as we go.
apatel336 0:1496281373a5 54 " ldrb r2, [r0], #1\n"
apatel336 0:1496281373a5 55 " lsls r2, r2, #8\n"
apatel336 0:1496281373a5 56 " subs r1, r1, #1\n"
apatel336 0:1496281373a5 57
apatel336 0:1496281373a5 58 // Need to 4-byte align? If not skip ahead.
apatel336 0:1496281373a5 59 "1$:\n"
apatel336 0:1496281373a5 60 " ands r4, r0, #3\n"
apatel336 0:1496281373a5 61 " beq 2$\n"
apatel336 0:1496281373a5 62 // Have more than 1 byte left to align? If not skip ahead to take care of
apatel336 0:1496281373a5 63 // trailing byte.
apatel336 0:1496281373a5 64 " cmp r1, #2\n"
apatel336 0:1496281373a5 65 " blt 7$\n"
apatel336 0:1496281373a5 66
apatel336 0:1496281373a5 67 // 4-byte align.
apatel336 0:1496281373a5 68 " ldrh r4, [r0], #2\n"
apatel336 0:1496281373a5 69 " adds r2, r2, r4\n"
apatel336 0:1496281373a5 70 " subs r1, r1, #2\n"
apatel336 0:1496281373a5 71
apatel336 0:1496281373a5 72 // Main summing loop which sums up data 2 words at a time.
apatel336 0:1496281373a5 73 // Make sure that we have more than 7 bytes left to sum.
apatel336 0:1496281373a5 74 "2$:\n"
apatel336 0:1496281373a5 75 " cmp r1, #8\n"
apatel336 0:1496281373a5 76 " blt 3$\n"
apatel336 0:1496281373a5 77 // Sum next two words. Applying previous upper 16-bit carry to
apatel336 0:1496281373a5 78 // lower 16-bits.
apatel336 0:1496281373a5 79 " ldr r4, [r0], #4\n"
apatel336 0:1496281373a5 80 " adds r2, r4\n"
apatel336 0:1496281373a5 81 " adc r2, r2, #0\n"
apatel336 0:1496281373a5 82 " ldr r4, [r0], #4\n"
apatel336 0:1496281373a5 83 " adds r2, r4\n"
apatel336 0:1496281373a5 84 " adc r2, r2, #0\n"
apatel336 0:1496281373a5 85 " subs r1, r1, #8\n"
apatel336 0:1496281373a5 86 " b 2$\n"
apatel336 0:1496281373a5 87
apatel336 0:1496281373a5 88 // Sum up any remaining half-words.
apatel336 0:1496281373a5 89 "3$:\n"
apatel336 0:1496281373a5 90 // Make sure that we have more than 1 byte left to sum.
apatel336 0:1496281373a5 91 " cmp r1, #2\n"
apatel336 0:1496281373a5 92 " blt 7$\n"
apatel336 0:1496281373a5 93 // Sum up next half word, continue to apply carry.
apatel336 0:1496281373a5 94 " ldrh r4, [r0], #2\n"
apatel336 0:1496281373a5 95 " adds r2, r4\n"
apatel336 0:1496281373a5 96 " adc r2, r2, #0\n"
apatel336 0:1496281373a5 97 " subs r1, r1, #2\n"
apatel336 0:1496281373a5 98 " b 3$\n"
apatel336 0:1496281373a5 99
apatel336 0:1496281373a5 100 // Handle trailing byte, if it exists
apatel336 0:1496281373a5 101 "7$:\n"
apatel336 0:1496281373a5 102 " cbz r1, 8$\n"
apatel336 0:1496281373a5 103 " ldrb r4, [r0]\n"
apatel336 0:1496281373a5 104 " adds r2, r4\n"
apatel336 0:1496281373a5 105 " adc r2, r2, #0\n"
apatel336 0:1496281373a5 106
apatel336 0:1496281373a5 107 // Fold 32-bit checksum into 16-bit checksum.
apatel336 0:1496281373a5 108 "8$:\n"
apatel336 0:1496281373a5 109 " ubfx r4, r2, #16, #16\n"
apatel336 0:1496281373a5 110 " ubfx r2, r2, #0, #16\n"
apatel336 0:1496281373a5 111 " adds r2, r4\n"
apatel336 0:1496281373a5 112 " ubfx r4, r2, #16, #16\n"
apatel336 0:1496281373a5 113 " ubfx r2, r2, #0, #16\n"
apatel336 0:1496281373a5 114 " adds r2, r4\n"
apatel336 0:1496281373a5 115
apatel336 0:1496281373a5 116 // Swap bytes if started at odd address
apatel336 0:1496281373a5 117 " cbz r3, 9$\n"
apatel336 0:1496281373a5 118 " rev16 r2, r2\n"
apatel336 0:1496281373a5 119
apatel336 0:1496281373a5 120 // Return final sum.
apatel336 0:1496281373a5 121 "9$: mov r0, r2\n"
apatel336 0:1496281373a5 122 " pop {r4, pc}\n"
apatel336 0:1496281373a5 123 );
apatel336 0:1496281373a5 124 }
apatel336 0:1496281373a5 125
apatel336 0:1496281373a5 126 #endif