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 23 /* Task tables and data. */ 24 25 enum { max_tasks = 3 }; 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 /* The unrelocated symbol table location. */ 40 41 extern u32 _got_copy_start; 42 43 /* Task management functions. */ 44 45 void init_tasks() 46 { 47 current_task = 0; 48 current_stack_pointer = &stack_pointers[current_task]; 49 current_registers = registers[current_task]; 50 } 51 52 void start_task(unsigned short task, void (*function)(), u32 args[], unsigned short nargs) 53 { 54 u32 virtual, physical; 55 56 /* 57 Each task employs a stack at a multiple of the given start address in 58 physical memory, but at the same address in virtual memory. 59 */ 60 61 virtual = stack_start; 62 physical = stack_start - stack_size * task; 63 64 init_page_table(page_table_start, virtual - pagesize * 2, physical - pagesize * 2, pagesize, 0x1e, task); 65 66 /* 67 Subtract from the stack pointer to prevent the called function from 68 reaching into unmapped memory. 69 */ 70 71 stack_pointers[task] = virtual - 12; 72 73 /* 74 Set the registers for the new task, initialising the global pointer and 75 return address. 76 */ 77 78 init_registers(registers[task], _got_copy_start, function, args, nargs); 79 } 80 81 void switch_task() 82 { 83 /* Switch the current task. */ 84 85 current_task++; 86 if (current_task == max_tasks) current_task = 0; 87 88 /* Indicate the current stack pointer and task registers. */ 89 90 current_stack_pointer = &stack_pointers[current_task]; 91 current_registers = registers[current_task]; 92 }