annotate doc/Tango-pinmux @ 688:5806383e2788

doc/Compiling: update for luna1, luna2 and tangomdm
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 12 Oct 2020 19:17:23 +0000
parents 52ee171ff5e4
children
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Mychaela Falconia <falcon@freecalypso.org>
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1 FreeCalypso Tango is a Calypso core module with the special quality of having
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2 many Calypso signals brought out on the user interface connector. Out of the
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3 great many Calypso signals that are brought out, the following 8 pins are
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4 subject to functional multiplexing concerns:
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5
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6 GPIO1
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7 GPIO2
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8 GPIO3
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9 RESET_OUT/GPIO7
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10 MCSI_TXD/GPIO9
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11 MCSI_RXD/GPIO10
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12 MCSI_CLK/GPIO11
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13 MCSI_FSYNCH/GPIO12
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14
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Mychaela Falconia <falcon@freecalypso.org>
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15 All 8 are capable of functioning as GPIOs, meaning that a Tango-based custom
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16 application board designer can use them for whatever purpose they like, but
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Mychaela Falconia <falcon@freecalypso.org>
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17 some of them can also be configured as dedicated Calypso peripheral pins,
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Mychaela Falconia <falcon@freecalypso.org>
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18 particularly MCSI. Others (GPIO1-3) have software-defined conventional
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Mychaela Falconia <falcon@freecalypso.org>
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19 functions based on long-standing tradition.
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20
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Mychaela Falconia <falcon@freecalypso.org>
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21 The special complication that arises for our firmware with regard to these GPIO
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Mychaela Falconia <falcon@freecalypso.org>
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22 and multifunction pins is that it is not our place as the firmware vendor to
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Mychaela Falconia <falcon@freecalypso.org>
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23 dictate to our potential customers how they should wire these pins on their
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Mychaela Falconia <falcon@freecalypso.org>
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24 boards. Instead an FC Tango customer should be able to wire up their board as
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25 their application calls for, subject to constraints imposed by hardware (not by
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26 firmware!), and our standard fw needs to work with every reasonable possibility
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27 for user wiring of our GPIO and multifunction pins. The following practical
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28 cases need to be addressed:
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29
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30 * If a customer chooses to use any of our GPIOs as an input, feeding some
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31 external output to it, there needs to be a way to tell our fw to leave that GPIO
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32 as an input and not switch it to an output.
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33
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34 * Conversely, if a given GPIO or multifunction pin is unused or not needed in a
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35 given application, the app board designer should have the freedom to either tie
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36 it off or leave it unconnected. If some of our GPIO or multifunction pins are
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37 left unconnected, this fact needs to be communicated to our fw so it can
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38 configure them as dummy outputs, preventing floating inputs.
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39
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Mychaela Falconia <falcon@freecalypso.org>
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40 * Some applications will use MCSI, while others won't. If a given application
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41 does not use MCSI, the 4 pins (or any subset of them) can be used as GPIOs,
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42 either inputs or outputs, or the unused pins may be left unconnected.
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43
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Mychaela Falconia <falcon@freecalypso.org>
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44 * GPIO3 is traditionally defined (by conventions going back to TI) as DTR input
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Mychaela Falconia <falcon@freecalypso.org>
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45 - but not every application will have a sensible DTR signal to feed to this pin.
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Mychaela Falconia <falcon@freecalypso.org>
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46 If there is no DTR signal in a given application, the app board designer should
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Mychaela Falconia <falcon@freecalypso.org>
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47 be able to either use GPIO3 for some unrelated purpose, or leave it unconnected.
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48
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Mychaela Falconia <falcon@freecalypso.org>
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49 * GPIO2 is similarly defined as DCD output by the same traditional conventions.
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50 Because it is an output from Calypso, it can be simply ignored and left
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Mychaela Falconia <falcon@freecalypso.org>
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51 unconnected if it is not needed - but a user should also be able to use the GPIO
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52 for unrelated purposes.
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53
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54 * There exist several historical conventional functions for GPIO1 output:
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55 loudspeaker control (D-Sample, Leonardo, FCDEV3B), Openmoko's application
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56 processor wake-up signal, or RI modem control output. We allow any of these
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57 options, plus other arbitrary uses.
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58
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59 FreeCalypso solution
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60 ====================
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61
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62 Our solution for firmware build target tangomdm (standard shipping fw for Tango
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63 modems) is that our fw will look on boot for a file in FFS named
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64 /etc/tango-pinmux; it will be a binary file of 4 bytes, defining pin
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65 multiplexing configuration as follows:
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66
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67 Byte 0: GPIO1 config
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68
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69 The following values are defined:
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70
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71 0x00: GPIO1 is left as an input from power-up
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72 0x80: GPIO1 is switched to an output, initial value 0
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73 0x81: GPIO1 is switched to an output, initial value 1
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74 0x82: GPIO1 is wake-up output per Openmoko GTA01/02 convention
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75 0x83: GPIO1 is RI output
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76
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77 Byte 1: GPIO2 and GPIO3 config
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78
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79 Bit 7: if 1, GPIO3 is DTR input, other bits in this nibble ignored
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80 if 0, GPIO3 is a "generic" GPIO (undefined function) per bits 5 and 4
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81 Bit 5: if 1, GPIO3 is an output, otherwise it's an input
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82 Bit 4: initial output value if GPIO3 is an output
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83
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84 Bit 3: if 1, GPIO2 is DCD output, other bits in this nibble ignored
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Mychaela Falconia <falcon@freecalypso.org>
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85 if 0, GPIO2 is a "generic" GPIO (undefined function) per bits 1 and 0
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86 Bit 1: if 1, GPIO2 is an output, otherwise it's an input
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87 Bit 0: initial output value if GPIO2 is a generic (not DCD) output
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88
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89 Byte 2: Peripheral pin mux config
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90
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91 Bit 7: if 0, MCSI pins retain their default power-up functions
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Mychaela Falconia <falcon@freecalypso.org>
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92 if 1, MCSI pins are switched to being GPIOs
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Mychaela Falconia <falcon@freecalypso.org>
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93
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Mychaela Falconia <falcon@freecalypso.org>
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94 Bit 3: if 0, RESET_OUT pin retains its default power-up function
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95 if 1, RESET_OUT pin is switched to being GPIO7
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96 Bit 1: if 1, GPIO7 is an output, otherwise it's an input
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97 bit 0: initial output value of GPIO7
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98
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99 Byte 3: I/O config of MCSI pins turned into GPIOs
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100
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101 This byte will be considered only if Byte 2 Bit 7 is set to 1, and will be
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Mychaela Falconia <falcon@freecalypso.org>
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102 ignored otherwise.
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103
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104 Bit 7: GPIO12 direction: 1 means output, 0 means input
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105 Bit 6: GPIO11 direction: 1 means output, 0 means input
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106 Bit 5: GPIO10 direction: 1 means output, 0 means input
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107 Bit 4: GPIO9 direction: 1 means output, 0 means input
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108
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109 Bit 3: GPIO12 initial output value
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110 Bit 2: GPIO11 initial output value
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Mychaela Falconia <falcon@freecalypso.org>
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111 Bit 1: GPIO10 initial output value
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Mychaela Falconia <falcon@freecalypso.org>
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112 Bit 0: GPIO9 initial output value
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113
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114 If the /etc/tango-pinmux file is missing, the effect will be the same as if all
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115 four bytes are equal to zero: GPIO1-3 will be functionally-undefined inputs,
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116 RESET_OUT/GPIO7 will be left as RESET_OUT from power-up, and all 4 MCSI pins
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117 will be likewise left in their power-up default MCSI function.
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118
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119 Any GPIO that is configured as an input can be read with AT+IOR, and any GPIO
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parents:
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120 that is configured as a generic (not built-in function) output can be set with
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Mychaela Falconia <falcon@freecalypso.org>
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121 AT+IOW.
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122
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123 Other GPIO pins
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124 ===============
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125
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126 Calypso pins GPIO0, TSPDI/GPIO4, BCLKX/GPIO6, MCUEN1/GPIO8 and MCUEN2/GPIO13
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127 are not brought out externally on Tango modules, thus they don't need to be
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Mychaela Falconia <falcon@freecalypso.org>
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128 considered. Our fw configures them as dummy outputs to prevent floating inputs.