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48 lines
1.9 KiB
Groff
48 lines
1.9 KiB
Groff
.TH L4_UTCB 7 2009-11-02 "Codezero" "Codezero Programmer's Manual"
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.SH NAME
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.nf
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.BR "UTCB" "- User visible thread control block"
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.SH SYNOPSIS
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.nf
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UTCB is a memory block designated as thread local storage that also serves as storage space for per-thread message registers transferred during an IPC between two threads.
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.fi
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.SH DESCRIPTION
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UTCB address is a virtual address that is unique for each thread available on the system and is discovered at run-time by reading the Kernel Interface Page.It also stores message registers that are transferred between threads during an IPC. Depending on whether the IPC is a send or a receive, the message register fields are either transferred to other threads, or overwritten by message registers of other threads. For details please refer to the
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.BR L4_IPC ()
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system call reference page.
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UTCB address pool is predefined by the microkernel, but each individual address is allocated by the pagers.
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.fi
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UTCB may contain thread-local information. Currently on the ARM architecture, the only fields on the UTCB that are not message registers are the
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.I saved_tag
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and
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.I saved_sender
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fields, which are used for saving the context of an earlier IPC if a new IPC is going to be made before finishing the first one in a stacked fashion.
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.fi
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The UTCB structure is subject to change. New fields may be reserved on the UTCB as needed.
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.ti 10
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.BI "struct " "utcb "
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{
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.ti 18
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.BI "u32 " "mr[MR_TOTAL]" "; /* MRs that are mapped to real registers */"
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.ti 18
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.BI "u32 " "saved_tag" "; /* Saved tag field for stacked ipcs */"
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.ti 18
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.BI "u32 " "saved_sender" "; /* Saved sender field for stacked ipcs */"
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.ti 18
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.BI "u32 " "mr_rest[MR_REST]" "; /* Complete the utcb for up to 64 words */"
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.ti 10
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};
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.in 8
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.SH L4 Userspace Library Functions
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.nf
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/* Functions to read/write utcb registers */
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.BI "static inline unsigned int read_mr(int " "offset");
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.BI "static inline void write_mr(unsigned int " "offset," "unsigned int " "val" ")"
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