FreeCalypso > hg > freecalypso-tools
annotate target-utils/libcommon/cmd_baud_switch.c @ 416:30f6d1c32c6f
doc/Flash-boot-defect article removed (no longer relevant)
This article is no longer relevant because the issue in question
only affected one (1) defective FCDEV3B board which was not
and never will be sold.
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Fri, 26 Oct 2018 07:11:08 +0000 |
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1 /* |
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2 * Baud rate switching command |
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3 */ |
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4 |
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5 #include <stdlib.h> |
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6 #include "types.h" |
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7 #include "ns16550.h" |
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8 |
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9 extern struct ns16550_regs *uart_base; |
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10 extern int serial_in_poll(); |
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11 |
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12 static const struct tab { |
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13 int baud; |
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14 int divisor; |
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15 } rate_table[] = { |
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16 /* |
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17 * First support the rates and divisors implemented by the |
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18 * Calypso boot ROM. Dividing 13 MHz by 7 gives an approximation |
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19 * of 115200 (x16); the divisors used by the boot ROM code for |
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20 * the slower baud rates are all 7x the usual PC value. |
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21 */ |
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22 {115200, 7}, |
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23 {57600, 7 * 2}, |
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24 {38400, 7 * 3}, |
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25 {28800, 7 * 4}, |
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26 {19200, 7 * 6}, |
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27 /* |
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28 * Going faster than ~115200 baud means using a divisor |
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29 * less than 7, resulting in a non-standard baud rate. |
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30 * The /1, /2 and /4 seem like reasonable choices. |
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31 */ |
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32 {812500, 1}, |
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33 {406250, 2}, |
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34 {203125, 4}, |
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35 /* that's all we really need to support */ |
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36 {0, 0} |
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37 }; |
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38 |
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39 /* |
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40 * The following helper function actually switches the UART |
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41 * baud rate divisor. Call serial_flush() first. It returns the |
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42 * old divisor value. |
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43 * |
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44 * Note the u8 type for both the new and old divisor values. |
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45 * All supported divisors are well below 255, so we don't bother |
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46 * with the upper byte. |
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47 */ |
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48 static u8 |
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49 actually_switch_baud(newdiv) |
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50 u8 newdiv; |
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51 { |
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52 volatile struct ns16550_regs *regs; |
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53 u8 save_lcr, save_old_baud; |
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54 |
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55 regs = uart_base; |
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56 save_lcr = regs->lcr; |
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57 regs->lcr = save_lcr | NS16550_LCR_DLAB; |
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58 save_old_baud = regs->datareg; |
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59 regs->datareg = newdiv; |
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60 regs->lcr = save_lcr; |
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61 return(save_old_baud); |
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62 } |
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63 |
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64 void |
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65 cmd_baud_switch(argbulk) |
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66 char *argbulk; |
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67 { |
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68 char *argv[2]; |
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69 int baudarg; |
108
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70 const struct tab *tp; |
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71 u8 save_old_baud; |
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72 int c; |
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73 |
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74 if (parse_args(argbulk, 1, 1, argv, 0) < 0) |
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75 return; |
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76 baudarg = atoi(argv[0]); |
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77 for (tp = rate_table; tp->baud; tp++) |
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78 if (tp->baud == baudarg) |
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79 break; |
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80 if (!tp->baud) { |
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81 printf("ERROR: invalid/unimplemented baud rate argument\n"); |
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82 return; |
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83 } |
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84 |
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85 /* do it */ |
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86 serial_flush(); |
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87 save_old_baud = actually_switch_baud(tp->divisor); |
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88 |
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89 /* |
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90 * After getting the echo of this command at the old baud rate |
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91 * (see the serial flush call just before switching the divisor), |
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92 * the line will go silent from the user's perspective. |
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93 * The user should wait just a little bit, then send us a 0x55 ('U') |
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94 * at the new baud rate - we should be in the below loop waiting |
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95 * for this character by then. Receiving that character |
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96 * correctly (0x55 was chosen for the bit pattern - unlikely to |
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97 * be received if the sender is sending at a wrong baud rate) |
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98 * will cause us to conclude this command and return a new '=' |
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99 * prompt at the new baud rate. |
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100 * |
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101 * If we get something else, we assume that someone messed up, |
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102 * switch back to the old baud rate, scribble an error message |
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103 * and return. |
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104 */ |
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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105 do |
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Mychaela Falconia <falcon@freecalypso.org>
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106 c = serial_in_poll(); |
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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107 while (c < 0); |
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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108 if (c != 0x55) { |
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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109 actually_switch_baud(save_old_baud); |
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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110 printf("ERROR: no \'U\' received, switched back to old baud rate\n"); |
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initial import from freecalypso-sw rev 1033:5ab737ac3ad7
Mychaela Falconia <falcon@freecalypso.org>
parents:
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111 } |
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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112 } |