FreeCalypso > hg > freecalypso-tools

annotate target-utils/libcommon/cmd_baud_switch.c @ 915:71edc12b1aa7

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doc/Rvinterf-tools: document new rvinterf -v option
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 29 Dec 2022 23:59:00 +0000
parents 2b041d57de1f
children
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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;
0
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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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105 do
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106 c = serial_in_poll();
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107 while (c < 0);
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108 if (c != 0x55) {
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109 actually_switch_baud(save_old_baud);
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110 printf("ERROR: no \'U\' received, switched back to old baud rate\n");
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111 }
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112 }