2 * xtos-params.h -- user-settable parameters for XTOS single-threaded run-time
4 * Copyright (c) 2002, 2004, 2006-2007 Tensilica Inc.
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31 * This file contains XTOS parameters that may be modified
32 * according to needs. HOWEVER, any modifications are NOT
33 * supported. Handling of parameters other than the defaults
34 * provided in the original version of this file are for
35 * illustrative and educational purposes only. If you do
36 * change the parameters here-in (which requires rebuilding
37 * XTOS), please verify the resulting code extensively
38 * before even considering its use in production code.
40 * To rebuild XTOS, see instructions in the Xtensa System Software
41 * Reference Manual. The following sequence is no longer supported.
43 * cd <config_dir>/xtensa-elf/src/handlers
48 * (Note: the last step installs the modified XTOS in *ALL*
49 * LSPs that normally include XTOS. You may prefer copying
50 * the generated files to your own custom LSP instead. Or
51 * better yet, also make a copy of all source files and maintain
52 * them somewhere completely separate -- which may require
53 * minor adjustments to the makefile.)
56 * To slightly improve performance of interrupt dispatching,
57 * you can do some combination of the following:
58 * - change XTOS_SUBPRI to zero
59 * - change XTOS_SUBPRI_GROUPS to zero
60 * - change XTOS_SUBPRI_ORDER to XTOS_SPO_ZERO_HI
61 * - change XTOS_DEBUG_PC to zero
62 * - change XTOS_INT_FAIRNESS to zero
63 * - change XTOS_CNEST to zero
64 * There are non-trivial trade-offs in making such changes however,
65 * such as loss of support (see important note above), loss of
66 * interrupt scheduling fairness, loss of ability to traceback
67 * interrupt handlers across interrupted code when debugging them,
68 * loss of supported for nested C functions, etc.
73 * Lower LOCKLEVEL to XCHAL_EXCM_LEVEL for improved interrupt latency
74 * if you don't register C handlers for high-priority interrupts and your
75 * high-priority handlers don't touch INTENABLE nor virtual priorities.
77 * XTOS_LOCKLEVEL is less meaningful but still relevant if XEA2 and SUBPRI is zero,
78 * ie. if INTENABLE doesn't get virtualized (XTOS_VIRTUAL_INTENABLE not set);
79 * in this case, it is the interrupt level at which INTENABLE accesses are guarded,
80 * so that interrupt handlers up to this level can safely manipulate INTENABLE.
82 #define XTOS_LOCKLEVEL XCHAL_NUM_INTLEVELS /* intlevel of INTENABLE register virtualization
83 (minimum is EXCM_LEVEL) */
86 * NOTE: the following four parameters (SUBPRI, SUBPRI_GROUPS, SUBPRI_ORDER, INT_FAIRNESS)
87 * are irrelevant and ignored for interrupt vectors to which only one interrupt is mapped.
90 #define XTOS_SUBPRI 1 /* set to 0 if you don't need sub-prioritization
91 within level-one interrupts via software;
92 for XEA2 configs, this might improve performance of
93 certain sections of code, because INTENABLE register
94 virtualization becomes unnecessary in this case */
96 /* Ignored unless SUBPRI set: */
97 #define XTOS_SUBPRI_GROUPS 1 /* support selective grouping of interrupts at the same priority */
99 #define XTOS_SUBPRI_ORDER XTOS_SPO_ZERO_LO /* one of XTOS_SPO_ZERO_LO, XTOS_SPO_ZERO_HI */
101 /* Ignored if SUBPRI set but SUBPRI_GROUPS is not (single interrupt per subpri),
102 * or if single interrupt configured at level/vector: */
103 #define XTOS_INT_FAIRNESS 1 /* disable round-robin/fifo scheduling of interrupt
104 handlers of a given level or sub-priority */
107 #define XTOS_DEBUG_PC 1 /* enable nice stack traceback showing interrupted code
108 when debugging interrupt or exception handler;
109 not implemented for high-priority handlers, or
112 #define XTOS_CNEST 1 /* enable support for nested C functions
113 (save/restore nested C function call-chain pointer) */
115 /* Current compilers only use ACC (not MRn) when MAC16 is enabled, so you can leave this 0 for performance: */
116 #define XTOS_SAVE_ALL_MAC16 0 /* set to save/restore MAC16 MRn registers */
118 /* Setting this might be useful to clear X's in hardware simulation a bit earlier, but
119 * should not be needed in production code: */
120 #define XTOS_RESET_UNNEEDED 0 /* set to reset more registers than are really needed */
122 #endif /* XTOS_PARAMS_H */