1 | Getting Started with uMon for the Beaglebone Black |
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2 | |
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3 | ======================================================================= |
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4 | Booting: |
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5 | ======================================================================= |
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6 | |
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7 | ----------------------------------------------------------------------- |
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8 | SD Card: |
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9 | ----------------------------------------------------------------------- |
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10 | The Beaglebone Black can boot uMon from an SD card using two different |
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11 | boot modes. The first boot mode is to boot using "raw" mode. The |
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12 | second boot mode is to boot from a FAT primary partition marked as |
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13 | bootable. The details and the steps required to set up the SD card |
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14 | for each of the boot modes are elaborated in the following two sections |
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15 | on SD card booting. For more information on "raw" mode and FAT mode, |
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16 | please refer to the AM335s TRM Sections 26.1.7.5.5 "MMC/SD Read Sector |
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17 | Procedure in Raw Mode" and 26.1.7.5.6 "MMC/SD Read Sector Procedure |
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18 | in FAT Mode" respectively. |
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19 | |
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20 | In order to boot uMon from an SD card using FAT mode, a GP Header must |
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21 | be prepended to the uMon image. In the case of booting uMon using |
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22 | "raw" mode, both a Configuration Header TOC Structure followed by a |
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23 | GP Header must be prepended to the uMon image. |
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24 | |
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25 | The GP Header is 8 bytes long where the first 4 bytes specify the size |
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26 | of the uMon image that will be transferred while the last 4 bytes |
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27 | specify both the destination address where the uMon image will be |
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28 | transferred to and the entry point. |
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29 | |
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30 | For information on the layout of the Configuration Header TOC Structure |
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31 | required for "raw" mode booting, please refer to the AM335x TRM |
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32 | Section 26.1.7.5.5.1 "Configuration Header". |
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33 | |
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34 | One thing worth mentioning is that the Beaglebone Black is connected to |
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35 | the SD card using MMC0 and as a result the size of the SD card must not |
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36 | be greater than 4GB. This is indicated in the AM335x TRM Section |
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37 | 26.1.7.5.2 "System Interconnection". |
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38 | |
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39 | In order to configure the Beaglebone Black to boot from an SD card, |
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40 | a uSD must be inserted and the boot switch held down while the board |
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41 | is powered up. Once the board is powered on, the boot switch can |
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42 | be released. If the attempt to boot from the uSD fails, the |
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43 | Beaglebone Black will fall back and attempt to boot using UART. |
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44 | As a result, this will provide a way to determine whether the boot |
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45 | from SD has succeeded or not. |
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46 | |
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47 | Before starting, it is recommended that the device that will be |
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48 | manipulated is verified to be the right device. An approach to |
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49 | determine the right device name assigned to the SD card is by |
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50 | observing the output of |
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51 | |
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52 | cat /proc/partitions |
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53 | |
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54 | before and after inserting the SD card. |
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55 | |
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56 | |
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57 | RAW MODE: |
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58 | |
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59 | In order to boot from an SD card using "raw" mode, the uMon image |
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60 | must be prepended with a Configuration Header TOC Structure and a |
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61 | GP Header. The GP Header is placed right after the Configuration |
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62 | Header TOC Structure. |
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63 | |
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64 | When uMon is built, a uMon image containing the necessary headers |
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65 | is already created and is located under ./build_BEAGLEBONEBLACK. |
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66 | |
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67 | The next step is to setup the SD card. Fortunately, the script |
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68 | ./sd_setup.sh can be used to automate the process of setting up |
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69 | an SD card for "raw" mode booting. To do so, invoke the script as |
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70 | |
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71 | ./sd_setup.sh RAW <device> |
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72 | |
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73 | <device> shown above and for the remainder of this document will |
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74 | refer to the SD card. |
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75 | |
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76 | The following information specify how to manually set up the SD |
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77 | card. |
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78 | |
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79 | With the proper headers prepended, the image is ready to be booted. |
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80 | In order for the Beaglebone Black/AM335x to boot the image, the |
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81 | image must be placed at one of the offsets |
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82 | 0x00000/0x20000/0x40000/0x60000. |
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83 | |
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84 | As an example, to place the uMon image at the first offset |
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85 | |
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86 | # Get the size of the uMon image to transfer into the SD card |
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87 | export UMON_IMG_SIZE=`wc --bytes <uMon image> | cut -f 1 -d ' '` |
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88 | |
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89 | # Transfer the uMon image at offset 0x00000 |
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90 | dd if=<uMon image> bs=1 count=$UMON_IMG_SIZE of=/dev/<device> |
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91 | |
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92 | where <uMon image> is the path to the uMon image prepended with a |
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93 | Configuration Header TOC Structure and a GP Header. |
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94 | |
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95 | |
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96 | FAT MODE: |
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97 | |
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98 | In FAT Mode, an "MLO" file is searched for in the root directory of |
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99 | a primary partition formatted as FAT12/FAT16 or FAT32 and marked |
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100 | bootable. This "MLO" file must contain a GP Header followed by the |
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101 | uMon image. When uMon is built, an "MLO" file is already created and |
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102 | is located in ./build_BEAGLEBONEBLACK. |
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103 | |
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104 | For convenience, preparing the SD card for FAT Mode booting has |
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105 | been automated through the use of the same aforementioned script, |
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106 | ./sd_setup.sh. |
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107 | |
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108 | Invoking the script in order to create an SD card for FAT mode booting |
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109 | is as follows: |
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110 | |
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111 | ./sd_setup.sh FAT <device> |
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112 | |
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113 | The script simply sets up a primary partition on the SD card, marks |
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114 | it as bootable, formats it as FAT16 and then transfers the MLO file |
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115 | under ./build_BEAGLEBONEBLACK to the root directory of the primary |
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116 | partition on the SD card. |
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117 | |
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118 | The following elaborates the sequence of steps on how exactly an SD |
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119 | card is prepared for FAT Mode booting for the Beaglebone Black |
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120 | to boot from. |
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121 | |
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122 | Assuming that the SD card has not been formatted yet... |
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123 | |
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124 | Just to be safe, clear out the partition table at the base of the SD |
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125 | card to start fresh. |
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126 | |
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127 | dd if=/dev/zero of=<device> bs=1M count=1 |
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128 | |
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129 | The next step is to create a primary partition with the filesystem |
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130 | type set to FAT16. This primary partition will be placed as an entry |
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131 | in an MBR located in the first sector of the SD card. Fortunately, |
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132 | these intial steps are taken care of by the fdisk utility. |
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133 | |
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134 | To allocate a partition that will be formatted as FAT16 and to create |
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135 | an entry for the partition in the MBR, |
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136 | |
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137 | fdisk <device> |
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138 | |
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139 | Suppose the SD card is registered under /dev as "sdc", this would be |
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140 | |
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141 | fdisk /dev/sdc |
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142 | |
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143 | fdisk will then present a command-line dialog. |
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144 | |
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145 | From here, a new partition must be created using 'n'. This partition |
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146 | must have a type of 0x06 for FAT16 which is set with 't' and with the |
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147 | size allocated to the partition to be at least 3MB. This size is the |
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148 | minimum size required and is more than enough to hold a uMon image and |
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149 | to allow for future expansion. It is recommended that not all of the |
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150 | sectors of the SD card are allocated to the FAT16 primary partition |
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151 | in order to provide room for the possibility of storing user data or |
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152 | perhaps a kernel. |
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153 | |
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154 | Once that is done, the next step is to mark the primary partition as |
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155 | bootable. This is done using the 'a' option. |
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156 | |
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157 | With all that in place, the partition can be verified before writing |
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158 | it to the SD card with 'p'. Once the partition has been verified, |
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159 | it can be written to the SD card using 'w'. |
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160 | |
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161 | After using fdisk to set up the partition, the new partition can be |
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162 | viewed under /dev. So for example, if the base of the SD card is given |
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163 | as /dev/sdc, then the newly created FAT16 partition will be given as |
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164 | /dev/sdc1. |
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165 | |
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166 | The next step is to format this partition as FAT16: |
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167 | |
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168 | mkfs.fat -f 2 -F 16 -M 0xF8 -s 1 -S 512 <device> |
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169 | |
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170 | with <device> set to the primary partition of the SD card. |
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171 | |
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172 | The final step is to place the "MLO" file in the root directory |
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173 | of the FAT16 primary partition. |
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174 | |
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175 | cd ~ |
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176 | mkdir mnt |
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177 | mount <device> mnt |
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178 | cp <path_to_umon>/ports/beagleboneblack/build_BEAGLEBONEBLACK/MLO mnt |
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179 | umount mnt |
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180 | rmdir mnt |
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181 | |
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182 | In the previous set of commands, <device> is set to the primary |
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183 | partition of the SD card that was recently formatted as FAT16. |
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184 | |
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185 | The SD card is now ready. |
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186 | |
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187 | |
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188 | ----------------------------------------------------------------------- |
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189 | UART: |
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190 | ----------------------------------------------------------------------- |
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191 | Unlike booting from SD, booting via UART does not require any GP |
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192 | Header, Configuration Header TOC Structure, or both to be prepended to |
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193 | the uMon image. The uMon image that will be booted using UART is |
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194 | boot.bin which is located in ./build_BEAGLEBONEBLACK. |
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195 | |
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196 | In order to boot from UART, a 3.3V USB-to-Serial cable is required, |
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197 | e.g. the FTDI USB TTL Serial cable is a possible option. |
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198 | |
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199 | The last requirement is to have a terminal emulator |
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200 | (e.g. minicom/picocom/etc.) set up to perform XMODEM transfers using |
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201 | 1K packets and 16-bit CRC. |
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202 | |
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203 | To initiate the UART booting procedure on the Beaglebone Black, ensure |
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204 | that there is no uSD card inserted and then hold the boot switch down |
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205 | while powering up the board. Once the board is powered on, the boot |
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206 | switch can be released. |
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207 | |
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208 | If a terminal emulator is set up already and connected to the serial |
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209 | port of the Beaglebone Black, the character 'C' will be outputted |
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210 | continuously. This indicates that the UART booting procedure has |
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211 | initiated and is waiting for an image to be transferred via UART. |
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212 | |
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213 | From here, the uMon image can now be transferred using the terminal |
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214 | emulator. |
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215 | |
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216 | For more information on the UART boot procedure, please refer to the |
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217 | AM335x TRM Section 26.1.8.5 "UART Boot Procedure". |
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218 | ======================================================================= |
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