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docs: Add description of using OPENSBI_EXTERNAL_SBI_TYPES

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Add description of using OPENSBI_EXTERNAL_SBI_TYPES in external
firmware code base.

Signed-off-by: Abner Chang <abner.chang@hpe.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
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Abner Chang 2020-01-08 12:54:34 +08:00 • committed by Anup Patel
parent e340bbf7b5
commit b28b8ac0d2
1 changed files with 21 additions and 0 deletions
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docs/library_usage.md
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@ -66,3 +66,24 @@ bootloader to service the following interrupts and traps:
**Note:** external firmwares or bootloaders can be more conservative by
forwarding all traps and interrupts to *sbi_trap_handler()*.
Definitions of OpenSBI Data Types for the External Firmware
-----------------------------------------------------------
OpenSBI can be built as library using external firmware build system such as EDK2
code base (The open source of UEFI firmware implementation) and linked with external
firmware drivers based on the external firmware architecture.
**OPENSBI_EXTERNAL_SBI_TYPES** identifier is introduced to *sbi_types.h* for selecting
external header file during the build preprocess in order to define OpensSBI data types
based on external firmware data type binding.
For example, *bool* is declared as *int* in sbi_types.h. However in EDK2 build system,
*bool* is declared as *BOOLEAN* which is defined as *unsigned char* data type.
External firmware can define **OPENSBI_EXTERNAL_SBI_TYPES** in CFLAGS and specify it to the
header file maintained in its code tree. However, the external build system has to address
the additional include directory for the external header file based on its own build system.
For example,
*-D***OPENSBI_EXTERNAL_SBI_TYPES***=OpensbiTypes.h*
Above tells *sbi_types.h* to refer to *OpensbiTypes.h* instead of using original definitions of
data types.