2_isa/src/bootrom.c

   1 /* bootROM, a very small bootloader for $NAME
   2  *
   3  * protocol details:
   4  * abbrv: H = Host, CPU = C
   5  *
   6  * value/cmd              | direction | comment
   7  * ------------------------------------------------------------
   8  * 'H'                    | H -> C    | enter bootROM ("HI")
   9  * 'O'                    | C -> H    | ack bootROM entry ("OH HAI")
  10  *
  11  * 'W'0xZZZZZZZZ0xYYYYYYYY| H -> C    | write instr (0xYY...Y) to
  12  *                                    | address (0xZZ...Z)
  13  * 'D'                    | C -> H    | instr write done
  14  *
  15  * 'R'0xZZZZZZZZ          | H -> C    | read instr from address (0xZZ..Z)
  16  * 'F'0xYYYYYYYY          | C -> H    | instr read done and return instr
  17  *
  18  * 'Q'0xZZZZZZZZ0xYYYYYYYY| H -> C    | write data (0xYY...Y) to
  19  *                                    | address (0xZZ...Z)
  20  * 'A'                    | C -> H    | data write done
  21  *
  22  * 'T'0xZZZZZZZZ          | H -> C    | read data from address (0xZZ..Z)
  23  * 'G'0xYYYYYYYY          | C -> H    | read done and return data
  24  *
  25  * 'J'0xZZZZZZZZ          | H -> C    | jump to address (0xZZ...Z)
  26  */
  27
  28 #define UART_BASE 0x1000
  29 #define UART_STATUS (UART_BASE+0x4)
  30 #define UART_RECV (UART_BASE+0x8)
  31 #define UART_TRANS (UART_BASE+0xC)
  32 #define UART_BAUD (UART_BAUD+0x10)
  33
  34 #define UART_TRANS_EMPTY 0
  35 #define UART_RECV_NEW 1
  36
  37 /* TODO:
  38  * - uart: clear new_receive bit after the byte is copied?
  39  *   (implementation issue...)
  40  */
  41
  42 /* {d,i}{read,write}{8,32}:
  43  * d ... data space
  44  * i ... instruction space
  45  */
  46
  47 typedef unsigned char u8;
  48 typedef unsigned int u32;
  49
  50 void send_byte(u8 x)
  51 {
  52         while(!(dread32(UART_STATUS) & (1 << UART_TRANS_EMPTY)));
  53         dwrite8(UART_TRANS, x);
  54 }
  55
  56 void send_word(u32 x)
  57 {
  58         send_byte((x >> 0) & 0xff);
  59         send_byte((x >> 8) & 0xff);
  60         send_byte((x >> 16) & 0xff);
  61         send_byte((x >> 24) & 0xff);
  62 }
  63
  64 u8 recv_byte(void)
  65 {
  66         u8 ret;
  67         while(!(dread32(UART_STATUS) & (1 << UART_RECV_NEW)));
  68         ret = dread8(UART_RECV);
  69 }
  70
  71 u32 recv_word(void)
  72 {
  73         u32 ret = 0;
  74         ret |= recv_byte() << 0;
  75         ret |= recv_byte() << 8;
  76         ret |= recv_byte() << 16;
  77         ret |= recv_byte() << 24;
  78 }
  79
  80 void bootrom(void)
  81 {
  82         u8 cmd;
  83         u32 addr, instr;
  84         for(;;) {
  85                 cmd = recv_byte();
  86                 switch(cmd) {
  87                         case 'W':
  88                                 addr = recv_word();
  89                                 instr = recv_word();
  90                                 /* write to programm space */
  91                                 iwrite32(addr, instr);
  92                                 send_byte('D');
  93                                 break;
  94                         case 'R':
  95                                 addr = recv_word();
  96                                 instr = iread32(addr);
  97                                 send_byte('F');
  98                                 send_word(instr);
  99                                 break;
 100                         case 'Q':
 101                                 addr = recv_word();
 102                                 instr = recv_word();
 103                                 /* write to data space */
 104                                 dwrite32(addr, instr);
 105                                 send_byte('A');
 106                                 break;
 107                         case 'T':
 108                                 addr = recv_word();
 109                                 instr = dread32(addr);
 110                                 send_byte('G');
 111                                 send_word(instr);
 112                                 break;
 113                         case 'J':
 114                                 addr = recv_word();
 115                                 jump_to_instr_mem(addr);
 116                                 /* this should never return ;) */
 117                                 break;
 118                         case 'H':
 119                         default:
 120                                 /* OH HAI */
 121                                 send_byte('O');
 122                                 break;
 123                 }
 124         }
 125 }
 126
 127 #define TIMEOUT_START 0x13371337
 128 #define DEFAULT_PROG_START 0x200
 129
 130 void main(void)
 131 {
 132         /* wait for timeout */
 133         u32 to = TIMEOUT_START;
 134         u8 rec;
 135
 136         /* until to is zeros */
 137         while(to != 0) {
 138                 to--;
 139                 if(dread32(UART_STATUS) & (1 << UART_RECV_NEW)) {
 140                         rec = read8(UART_RECV);
 141                         if(rec == 'H') {
 142                                 send_byte('O');
 143                                 bootrom();
 144                         }
 145                 }
 146         }
 147
 148         /* after timeout jump to instr. mem plz */
 149         jump_to_instr_mem(DEFAULT_PROG_START);
 150 }