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 "cpu_op.h" 22 #include "paging.h" 23 #include "tasks.h" 24 25 /* Task tables and data. */ 26 27 static u32 stack_pointers[max_tasks]; 28 static u32 registers[max_tasks][32]; 29 30 u8 current_task; 31 u32 *current_stack_pointer; 32 u32 *current_registers; 33 34 /* Address locations and paging configuration. */ 35 36 const u32 stack_start = 0x00080000; 37 const u32 stack_size = 0x00002000; 38 const u32 pagesize = 4 * 1024; 39 40 /* A reference to locations for the symbol tables. */ 41 42 extern u32 _got_start, _got_copy_start, _got_copy_end; 43 44 /* A reference to the start of the payload and end of memory locations. */ 45 46 extern u32 _payload_start, _memory_end; 47 48 /* Task management functions. */ 49 50 void init_tasks() 51 { 52 current_task = 1; 53 init_task(); 54 } 55 56 void init_task() 57 { 58 current_stack_pointer = &stack_pointers[current_task]; 59 current_registers = registers[current_task]; 60 } 61 62 void start_task(unsigned short task, void (*function)(), u32 args[], u8 nargs) 63 { 64 u32 virtual, physical, address; 65 66 /* 67 Each task employs a stack at a multiple of the given start address in 68 physical memory, but at the same address in virtual memory. 69 */ 70 71 virtual = stack_start; 72 physical = stack_start - stack_size * task; 73 74 init_page_table(page_table_start, virtual - pagesize * 2, physical - pagesize * 2, pagesize, 0x1e, task); 75 76 /* 77 Subtract from the stack pointer to prevent the called function from 78 reaching into unmapped memory. 79 */ 80 81 stack_pointers[task] = virtual - 12; 82 83 /* 84 Set the registers for the new task, initialising the global pointer and 85 return address. 86 */ 87 88 init_registers(registers[task], (u32) &_got_copy_start, function, args, nargs); 89 90 /* Map the global object table for the task. */ 91 92 init_page_table(page_table_start, user_address((u32) &_got_start), user_address((u32) &_got_copy_start), pagesize, 0x1e, task); 93 94 /* Map all shared pages for the task. */ 95 96 for (address = (u32) &_payload_start; address < (u32) &_got_start; address += pagesize * 2) 97 { 98 init_page_table(page_table_start, user_address(address), user_address(address), pagesize, 0x1e, task); 99 } 100 101 for (address = (u32) &_got_copy_end + pagesize * 2; address < (u32) &_memory_end; address += pagesize * 2) 102 { 103 init_page_table(page_table_start, user_address(address), user_address(address), pagesize, 0x1e, task); 104 } 105 } 106 107 void start_task_now() 108 { 109 invoke_task(current_task, current_registers, current_stack_pointer); 110 } 111 112 void switch_task() 113 { 114 /* Switch the current task. */ 115 116 current_task++; 117 if (current_task == max_tasks) current_task = 1; 118 init_task(); 119 }