1 /* 2 * Task handling. 3 * 4 * Copyright (C) 2015, 2016 Paul Boddie <paul@boddie.org.uk> 5 * 6 * This program is free software: you can redistribute it and/or modify 7 * it under the terms of the GNU General Public License as published by 8 * the Free Software Foundation, either version 3 of the License, or 9 * (at your option) any later version. 10 * 11 * This program is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU General Public License for more details. 15 * 16 * You should have received a copy of the GNU General Public License 17 * along with this program. If not, see <http://www.gnu.org/licenses/>. 18 */ 19 20 #include "cpu.h" 21 #include "paging.h" 22 #include "tasks.h" 23 24 /* Task tables and data. */ 25 26 static u32 stack_pointers[max_tasks]; 27 static u32 registers[max_tasks][32]; 28 29 u8 current_task; 30 u32 *current_stack_pointer; 31 u32 *current_registers; 32 33 /* Address locations and paging configuration. */ 34 35 const u32 stack_start = 0x00080000; 36 const u32 stack_size = 0x00002000; 37 const u32 pagesize = 4 * 1024; 38 39 /* 40 References to the unrelocated symbol table and to the relocated version, both in 41 their original locations. 42 */ 43 44 extern u32 _got_start, _got_copy_start; 45 46 /* Regions to be mapped directly. */ 47 48 extern u32 _shared_start, _shared_end; 49 50 /* Task management functions. */ 51 52 void init_tasks() 53 { 54 current_task = 1; 55 init_task(); 56 } 57 58 void init_task() 59 { 60 current_stack_pointer = &stack_pointers[current_task]; 61 current_registers = registers[current_task]; 62 } 63 64 void start_task(unsigned short task, void (*function)(), u32 args[], u8 nargs) 65 { 66 u32 virtual, physical, address; 67 68 /* 69 Each task employs a stack at a multiple of the given start address in 70 physical memory, but at the same address in virtual memory. 71 */ 72 73 virtual = stack_start; 74 physical = stack_start - stack_size * task; 75 76 init_page_table(page_table_start, virtual - pagesize * 2, physical - pagesize * 2, pagesize, 0x1e, task); 77 78 /* Map shared pages. */ 79 80 for (address = (u32) &_shared_start; address < (u32) &_shared_end; address += pagesize * 2) 81 { 82 address = address & 0x7fffffff; 83 init_page_table(page_table_start, address, address, pagesize, 0x1e, task); 84 } 85 86 /* Map the task's global object table to the relocated version. */ 87 88 init_page_table(page_table_start, (u32) &_got_start & 0x7fffffff, (u32) &_got_copy_start & 0x7fffffff, pagesize, 0x1e, task); 89 90 /* 91 Subtract from the stack pointer to prevent the called function from 92 reaching into unmapped memory. 93 */ 94 95 stack_pointers[task] = virtual - 12; 96 97 /* 98 Set the registers for the new task, initialising the global pointer and 99 return address. 100 */ 101 102 init_registers(registers[task], (u32) &_got_start, function, args, nargs); 103 } 104 105 void start_task_now() 106 { 107 invoke_task(current_task, current_registers, current_stack_pointer); 108 } 109 110 void switch_task() 111 { 112 /* Switch the current task. */ 113 114 current_task++; 115 if (current_task == max_tasks) current_task = 1; 116 init_task(); 117 }