| rjw | 1f88458 | 2022-01-06 17:20:42 +0800 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright (c) 2013 Google Inc. |
| 3 | * |
| 4 | * Permission is hereby granted, free of charge, to any person obtaining |
| 5 | * a copy of this software and associated documentation files |
| 6 | * (the "Software"), to deal in the Software without restriction, |
| 7 | * including without limitation the rights to use, copy, modify, merge, |
| 8 | * publish, distribute, sublicense, and/or sell copies of the Software, |
| 9 | * and to permit persons to whom the Software is furnished to do so, |
| 10 | * subject to the following conditions: |
| 11 | * |
| 12 | * The above copyright notice and this permission notice shall be |
| 13 | * included in all copies or substantial portions of the Software. |
| 14 | * |
| 15 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, |
| 16 | * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF |
| 17 | * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. |
| 18 | * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY |
| 19 | * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, |
| 20 | * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE |
| 21 | * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |
| 22 | */ |
| 23 | #include <compiler.h> |
| 24 | #include <kernel/debug.h> |
| 25 | |
| 26 | __ALIGNED(8) __NAKED |
| 27 | #if (__CORTEX_M >= 0x03) || (CORTEX_SC >= 300) |
| 28 | |
| 29 | void spin_cycles(uint32_t cycles) |
| 30 | { |
| 31 | asm ( |
| 32 | /* 4 cycles per loop, subtract out 8 cycles for the overhead of the next |
| 33 | * 4 instructions, plus the call into and return from the function. |
| 34 | * Then, add 3 then >> 2 to round up to the number of loop iterations. |
| 35 | */ |
| 36 | "subs r1, %[cycles], #5\n" |
| 37 | "asrs r1, r1, #2\n" |
| 38 | "ble .Ldone\n" |
| 39 | |
| 40 | /* Padding to stay aligned on an 8 byte boundary, also has the added |
| 41 | * advantage of normalizing the overhead (1+1+2 cycles if the branch is |
| 42 | * take, or 1+1+1+1 cycles if the branch is skipped and the nop is |
| 43 | * executed) |
| 44 | */ |
| 45 | "nop\n" |
| 46 | |
| 47 | /* Main delay loop. |
| 48 | * sub is 1 cycle |
| 49 | * nop is 1 cycle |
| 50 | * branch is 2 cycles |
| 51 | */ |
| 52 | ".Lloop:\n" |
| 53 | "subs r1, r1, #1\n" |
| 54 | "nop\n" |
| 55 | "bne .Lloop\n" |
| 56 | |
| 57 | ".Ldone:\n" |
| 58 | "bx lr\n" |
| 59 | : /* no output */ |
| 60 | : [cycles] "r" (cycles) /* input is cycles */ |
| 61 | : "r1" /* r1 gets clobbered */ |
| 62 | ); |
| 63 | } |
| 64 | |
| 65 | #else |
| 66 | /* Cortex-M0 & Cortex-M0+ */ |
| 67 | void spin_cycles(uint32_t cycles) |
| 68 | { |
| 69 | asm ( |
| 70 | /* 4 cycles per loop, subtract out 8 cycles for the overhead of the next |
| 71 | * 4 instructions, plus the call into and return from the function. |
| 72 | * Then, add 3 then >> 2 to round up to the number of loop iterations. |
| 73 | */ |
| 74 | "sub r1, %[cycles], #5\n" |
| 75 | "asr r1, r1, #2\n" |
| 76 | "cmp r1, #0\n" |
| 77 | "ble .Ldone\n" |
| 78 | |
| 79 | /* Padding to stay aligned on an 8 byte boundary, also has the added |
| 80 | * advantage of normalizing the overhead (1+1+2 cycles if the branch is |
| 81 | * take, or 1+1+1+1 cycles if the branch is skipped and the nop is |
| 82 | * executed) |
| 83 | */ |
| 84 | "nop\n" |
| 85 | |
| 86 | /* Main delay loop. |
| 87 | * sub is 1 cycle |
| 88 | * nop is 1 cycle |
| 89 | * branch is 2 cycles |
| 90 | */ |
| 91 | ".Lloop:\n" |
| 92 | "sub r1, r1, #1\n" |
| 93 | "cmp r1,#0\n" |
| 94 | "bne .Lloop\n" |
| 95 | |
| 96 | ".Ldone:\n" |
| 97 | "bx lr\n" |
| 98 | : /* no output */ |
| 99 | : [cycles] "r" (cycles) /* input is cycles */ |
| 100 | : "r1" /* r1 gets clobbered */ |
| 101 | ); |
| 102 | } |
| 103 | #endif |