1 | .. comment SPDX-License-Identifier: CC-BY-SA-4.0 |
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2 | |
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3 | .. Copyright (C) 1988, 2002 On-Line Applications Research Corporation (OAR) |
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4 | |
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5 | Real-Time Clock Driver |
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6 | ********************** |
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7 | |
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8 | Introduction |
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9 | ============ |
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10 | |
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11 | The Real-Time Clock (*RTC*) driver is responsible for providing an interface to |
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12 | an *RTC* device. The capabilities provided by this driver are: |
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13 | |
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14 | - Set the RTC TOD to RTEMS TOD |
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15 | |
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16 | - Set the RTEMS TOD to the RTC TOD |
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17 | |
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18 | - Get the RTC TOD |
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19 | |
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20 | - Set the RTC TOD to the Specified TOD |
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21 | |
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22 | - Get the Difference Between the RTEMS and RTC TOD |
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23 | |
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24 | .. note:: |
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25 | |
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26 | In this chapter, the abbreviation `TOD` is used for *Time of Day*. |
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27 | |
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28 | The reference implementation for a real-time clock driver can be found in |
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29 | `bsps/shared/dev/rtc/rtc-support.c <https://git.rtems.org/rtems/tree/bsps/shared/dev/rtc/rtc-support.c>`_. |
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30 | This driver is based on the libchip concept and can be easily configured to |
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31 | work with any of the RTC chips supported by the RTC chip drivers in the |
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32 | directory |
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33 | `bsps/shared/dev/rtc <https://git.rtems.org/rtems/tree/bsps/shared/dev/rtc>`_. |
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34 | There is a README file in this directory for each supported RTC chip. Each of |
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35 | these README explains how to configure the shared libchip implementation of the |
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36 | RTC driver for that particular RTC chip. |
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37 | |
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38 | The DY-4 DMV177 BSP used the shared libchip implementation of the RTC driver. |
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39 | There were no DMV177 specific configuration routines. A BSP could use |
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40 | configuration routines to dynamically determine what type of real-time clock is |
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41 | on a particular board. This would be useful for a BSP supporting multiple |
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42 | board models. The relevant ports of the DMV177's ``RTC_Table`` configuration |
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43 | table is below: |
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44 | |
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45 | .. code-block:: c |
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46 | |
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47 | #include <bsp.h> |
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48 | #include <libchip/rtc.h> |
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49 | #include <libchip/icm7170.h> |
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50 | |
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51 | bool dmv177_icm7170_probe(int minor); |
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52 | |
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53 | rtc_tbl RTC_Table[] = { |
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54 | { "/dev/rtc0", /* sDeviceName */ |
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55 | RTC_ICM7170, /* deviceType */ |
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56 | &icm7170_fns, /* pDeviceFns */ |
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57 | dmv177_icm7170_probe, /* deviceProbe */ |
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58 | (void *) ICM7170_AT_1_MHZ, /* pDeviceParams */ |
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59 | DMV170_RTC_ADDRESS, /* ulCtrlPort1 */ |
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60 | 0, /* ulDataPort */ |
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61 | icm7170_get_register_8, /* getRegister */ |
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62 | icm7170_set_register_8, /* setRegister */ |
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63 | } |
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64 | }; |
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65 | unsigned long RTC_Count = (sizeof(RTC_Table)/sizeof(rtc_tbl)); |
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66 | rtems_device_minor_number RTC_Minor; |
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67 | |
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68 | bool dmv177_icm7170_probe(int minor) |
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69 | { |
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70 | volatile unsigned16 *card_resource_reg; |
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71 | card_resource_reg = (volatile unsigned16 *) DMV170_CARD_RESORCE_REG; |
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72 | if ( (*card_resource_reg & DMV170_RTC_INST_MASK) == DMV170_RTC_INSTALLED ) |
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73 | return TRUE; |
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74 | return FALSE; |
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75 | } |
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76 | |
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77 | Initialization |
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78 | ============== |
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79 | |
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80 | The ``rtc_initialize`` routine is responsible for initializing the RTC chip so |
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81 | it can be used. The shared libchip implementation of this driver supports |
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82 | multiple RTCs and bases its initialization order on the order the chips are |
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83 | defined in the ``RTC_Table``. Each chip defined in the table may or may not be |
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84 | present on this particular board. It is the responsibility of the |
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85 | ``deviceProbe`` to indicate the presence of a particular RTC chip. The first |
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86 | RTC found to be present is considered the preferred RTC. |
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87 | |
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88 | In the shared libchip based implementation of the driver, the following actions |
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89 | are performed: |
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90 | |
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91 | .. code-block:: c |
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92 | |
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93 | rtems_device_driver rtc_initialize( |
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94 | rtems_device_major_number major, |
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95 | rtems_device_minor_number minor_arg, |
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96 | void *arg |
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97 | ) |
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98 | { |
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99 | for each RTC configured in RTC_Table |
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100 | if the deviceProbe for this RTC indicates it is present |
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101 | set RTC_Minor to this device |
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102 | set RTC_Present to TRUE |
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103 | break out of this loop |
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104 | |
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105 | if RTC_Present is not TRUE |
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106 | return RTEMS_INVALID_NUMBER to indicate that no RTC is present |
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107 | |
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108 | register this minor number as the "/dev/rtc" |
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109 | |
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110 | perform the deviceInitialize routine for the preferred RTC chip |
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111 | |
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112 | for RTCs past this one in the RTC_Table |
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113 | if the deviceProbe for this RTC indicates it is present |
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114 | perform the deviceInitialize routine for this RTC chip |
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115 | register the configured name for this RTC |
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116 | } |
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117 | |
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118 | The ``deviceProbe`` routine returns TRUE if the device configured by this entry |
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119 | in the ``RTC_Table`` is present. This configuration scheme allows one to |
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120 | support multiple versions of the same board with a single BSP. For example, if |
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121 | the first generation of a board had Vendor A's RTC chip and the second |
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122 | generation had Vendor B's RTC chip, RTC_Table could contain information for |
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123 | both. The ``deviceProbe`` configured for Vendor A's RTC chip would need to |
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124 | return TRUE if the board was a first generation one. The ``deviceProbe`` |
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125 | routines are very board dependent and must be provided by the BSP. |
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126 | |
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127 | setRealTimeToRTEMS |
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128 | ================== |
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129 | |
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130 | The ``setRealTimeToRTEMS`` routine sets the current RTEMS TOD to that |
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131 | of the preferred RTC. |
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132 | |
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133 | .. code-block:: c |
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134 | |
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135 | void setRealTimeToRTEMS(void) |
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136 | { |
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137 | if no RTCs are present |
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138 | return |
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139 | |
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140 | invoke the deviceGetTime routine for the preferred RTC |
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141 | set the RTEMS TOD using rtems_clock_set |
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142 | } |
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143 | |
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144 | setRealTimeFromRTEMS |
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145 | ==================== |
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146 | |
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147 | The ``setRealTimeFromRTEMS`` routine sets the preferred RTC TOD to the |
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148 | current RTEMS TOD. |
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149 | |
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150 | .. code-block:: c |
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151 | |
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152 | void setRealTimeFromRTEMS(void) |
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153 | { |
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154 | if no RTCs are present |
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155 | return |
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156 | |
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157 | obtain the RTEMS TOD using rtems_clock_get |
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158 | invoke the deviceSetTime routine for the preferred RTC |
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159 | } |
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160 | |
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161 | getRealTime |
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162 | =========== |
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163 | |
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164 | The ``getRealTime`` returns the preferred RTC TOD to the caller. |
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165 | |
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166 | .. code-block:: c |
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167 | |
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168 | void getRealTime( rtems_time_of_day *tod ) |
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169 | { |
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170 | if no RTCs are present |
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171 | return |
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172 | |
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173 | invoke the deviceGetTime routine for the preferred RTC |
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174 | } |
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175 | |
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176 | setRealTime |
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177 | =========== |
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178 | |
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179 | The ``setRealTime`` routine sets the preferred RTC TOD to the TOD specified by |
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180 | the caller. |
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181 | |
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182 | .. code-block:: c |
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183 | |
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184 | void setRealTime( rtems_time_of_day *tod ) |
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185 | { |
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186 | if no RTCs are present |
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187 | return |
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188 | |
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189 | invoke the deviceSetTime routine for the preferred RTC |
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190 | } |
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191 | |
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192 | checkRealTime |
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193 | ============= |
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194 | |
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195 | The ``checkRealTime`` routine returns the number of seconds difference between |
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196 | the RTC TOD and the current RTEMS TOD. |
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197 | |
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198 | .. code-block:: c |
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199 | |
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200 | int checkRealTime( void ) |
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201 | { |
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202 | if no RTCs are present |
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203 | return -1 |
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204 | |
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205 | obtain the RTEMS TOD using rtems_clock_get |
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206 | get the TOD from the preferred RTC using the deviceGetTime routine |
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207 | convert the RTEMS TOD to seconds |
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208 | convert the RTC TOD to seconds |
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209 | |
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210 | return the RTEMS TOD in seconds - RTC TOD in seconds |
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211 | } |
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