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Add RISC OS Select documentation for NVRAMV.
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| <?xml version="1.0"?> | ||
| <!DOCTYPE riscos-prm PUBLIC "-//Gerph//DTD PRM documentation 1.03//EN" | ||
| "http://gerph.org/dtd/103/prm.dtd"> | ||
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| <riscos-prm> | ||
| <chapter title="NVRAM vector"> | ||
| <section title="Introduction"> | ||
| <p> | ||
| The RISC OS system uses memory which is preserved whilst the power | ||
| is off to store configuration information. This allows the system | ||
| to start with the correct settings such as hardware configuration | ||
| and user preferences. Examples of hardware configuration are settings | ||
| such as the filing system to boot from and which drive should be | ||
| used. User preferences include the type and volume of system beep. | ||
| </p> | ||
| </section> | ||
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| <section title="Technical details"> | ||
| <p> | ||
| Under earlier versions of the operating system the non-volatile RAM | ||
| ('NVRAM', also referred to as CMOS RAM, or battery backed RAM) was handled | ||
| entirely by the Kernel. From Kernel 9.48, the handling of NVRAM is delegated | ||
| to hardware support modules. The Kernel communicates with these modules | ||
| through the vector NVRAMV. | ||
| </p> | ||
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| <p> | ||
| Driver modules which provide the NVRAMV vector should be initialised | ||
| with the early initialisation flag (module flags bit 1) set. This allows | ||
| the modules to be started before the configuration for unplugged modules | ||
| is required. | ||
| </p> | ||
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| <category title="Terminology"> | ||
| <p>The configuration data handled by NVRAMV has generally been termed | ||
| 'CMOS' or 'CMOS data'. Historically, the configuration information was | ||
| used CMOS technology to store the contents of the memory, but this is | ||
| not required. The name 'non-volative RAM' is a more general term which | ||
| does not imply the use of a particular technology, so is used to | ||
| describe the mecanishm for storing the configuration data. | ||
| </p> | ||
| </category> | ||
| </section> | ||
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| <section title="Software vectors"> | ||
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| <vector-definition name="NVRAMV" | ||
| number="3E" | ||
| description="Operations on non-volatile memory used for configuration" | ||
| irqs="undefined" | ||
| fiqs="enabled" | ||
| processor-mode="SVC" | ||
| re-entrant="no" | ||
| > | ||
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||
| <entry> | ||
| <register-use number="0">reason code: | ||
| <p> | ||
| <value-table> | ||
| <value number="0"><reference type="vector" name="NVRAMV" reason="0" use-description="yes" /></value> | ||
| <value number="1"><reference type="vector" name="NVRAMV" reason="1" use-description="yes" /></value> | ||
| <value number="2"><reference type="vector" name="NVRAMV" reason="2" use-description="yes" /></value> | ||
| </value-table> | ||
| </p> | ||
| </register-use> | ||
| </entry> | ||
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| <exit> | ||
| <register-use number="0">-1 if handled, preserved if not handled</register-use> | ||
| <register-use number="1-9">dependant on reason code</register-use> | ||
| </exit> | ||
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| <use> | ||
| <p>This vector is called by the Kernel to control the configuration data stored | ||
| in the NVRAM. | ||
| </p> | ||
| </use> | ||
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| <related> | ||
| <reference type="swi" name="OS_Byte" reason="161" href="?" /> | ||
| <reference type="swi" name="OS_Byte" reason="162" href="?" /> | ||
| </related> | ||
| </vector-definition> | ||
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| <vector-definition name="NVRAMV" | ||
| number="3E" | ||
| reason="0" | ||
| reasonname="FillCache" | ||
| description="Populate the cache with NVRAM data" | ||
| irqs="undefined" | ||
| fiqs="enabled" | ||
| processor-mode="SVC" | ||
| re-entrant="no" | ||
| > | ||
| <entry> | ||
| <register-use number="0">0 (reason code)</register-use> | ||
| <register-use number="1">pointer to cache block to fill</register-use> | ||
| <register-use number="2">number of bytes to fill</register-use> | ||
| </entry> | ||
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| <exit> | ||
| <register-use number="0">-1 (operation complete)</register-use> | ||
| <register-use number="1" state="preserved"/> | ||
| <register-use number="2">number of bytes populated</register-use> | ||
| </exit> | ||
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| <use> | ||
| <p>This vector is called by the Kernel to fill in its cache of NVRAM values. | ||
| A cache is provided in order to reduce the impact of repeated reading of | ||
| configuration data by clients. Clients should write 0 to the cache for | ||
| unsupported values. The number of bytes to fill may take any value. The | ||
| total amount of NVRAM should be returned, not the amount of NVRAM filled. | ||
| Only the first 240 bytes of NVRAM will be used by the Kernel initially. | ||
| </p> | ||
| </use> | ||
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| <related> | ||
| </related> | ||
| </vector-definition> | ||
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| <vector-definition name="NVRAMV" | ||
| number="3E" | ||
| reason="1" | ||
| reasonname="ReadByte" | ||
| description="Read a single value from NVRAM" | ||
| irqs="undefined" | ||
| fiqs="enabled" | ||
| processor-mode="SVC" | ||
| re-entrant="no" | ||
| > | ||
| <entry> | ||
| <register-use number="0">1 (reason code)</register-use> | ||
| <register-use number="1">byte to read</register-use> | ||
| </entry> | ||
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| <exit> | ||
| <register-use number="0">-1 (operation complete)</register-use> | ||
| <register-use number="1">value read, or 0 if byte is out of range</register-use> | ||
| </exit> | ||
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| <use> | ||
| <p>This vector is called by the Kernel to read a single value. It will usually | ||
| only be used before the NVRAM cache has been populated during system | ||
| initialisation. | ||
| </p> | ||
| </use> | ||
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| <related> | ||
| <reference type="swi" name="OS_Byte" reason="161" href="?" /> | ||
| </related> | ||
| </vector-definition> | ||
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| <vector-definition name="NVRAMV" | ||
| number="3E" | ||
| reason="2" | ||
| reasonname="WriteByte" | ||
| description="Write a single value to NVRAM" | ||
| irqs="undefined" | ||
| fiqs="enabled" | ||
| processor-mode="SVC" | ||
| re-entrant="no" | ||
| > | ||
| <entry> | ||
| <register-use number="0">2 (reason code)</register-use> | ||
| <register-use number="1">byte to read</register-use> | ||
| </entry> | ||
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| <exit> | ||
| <register-use number="0">-1 (operation complete)</register-use> | ||
| <register-use number="1">value read, or 0 if byte is out of range</register-use> | ||
| </exit> | ||
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| <use> | ||
| <p>This vector is called by the Kernel to write a single value to the NVRAM.</p> | ||
| </use> | ||
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| <related> | ||
| <reference type="swi" name="OS_Byte" reason="162" href="?" /> | ||
| </related> | ||
| </vector-definition> | ||
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| </section> | ||
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| </chapter> | ||
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| <!-- MetaData --> | ||
| <meta> | ||
| <maintainer> | ||
| <email name="Gerph" address="[email protected]" /> | ||
| </maintainer> | ||
| <disclaimer> | ||
| <p> | ||
| © Gerph, 2023. | ||
| </p> | ||
| </disclaimer> | ||
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| <history> | ||
| <revision number="1" author="Gerph" date="31 May 2023" title="Initial version"> | ||
| <change>Created from Select technical documentation.</change> | ||
| </revision> | ||
| </history> | ||
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| <related> | ||
| <reference type='link' href="http://www.riscos.com/support/developers/riscos6/hardware/nvramv.html" /> | ||
| </related> | ||
| </meta> | ||
| </riscos-prm> |