diff options
Diffstat (limited to 'nuttx/configs')
| -rw-r--r-- | nuttx/configs/README.txt | 34 |
1 files changed, 29 insertions, 5 deletions
diff --git a/nuttx/configs/README.txt b/nuttx/configs/README.txt index 6c3a0b74a..21426362f 100644 --- a/nuttx/configs/README.txt +++ b/nuttx/configs/README.txt @@ -489,15 +489,39 @@ defconfig -- This is a configuration file similar to the Linux The architecture can provide optimized versions of the following to improve system performance - CONFIG_ARCH_MEMCPY, CONFIG_ARCH_MEMCMP, CONFIG_ARCH_MEMMOVE - CONFIG_ARCH_MEMSET, CONFIG_ARCH_STRCMP, CONFIG_ARCH_STRCPY - CONFIG_ARCH_STRNCPY, CONFIG_ARCH_STRLEN, CONFIG_ARCH_STRNLEN - CONFIG_ARCH_BZERO + CONFIG_ARCH_MEMCPY, CONFIG_ARCH_MEMCMP, CONFIG_ARCH_MEMMOVE + CONFIG_ARCH_MEMSET, CONFIG_ARCH_STRCMP, CONFIG_ARCH_STRCPY + CONFIG_ARCH_STRNCPY, CONFIG_ARCH_STRLEN, CONFIG_ARCH_STRNLEN + CONFIG_ARCH_BZERO The architecture may provide custom versions of certain standard header files: - CONFIG_ARCH_MATH_H, CONFIG_ARCH_STDBOOL_H, CONFIG_ARCH_STDINT_H + CONFIG_ARCH_MATH_H, CONFIG_ARCH_STDBOOL_H, CONFIG_ARCH_STDINT_H + + CONFIG_ARCH_ROMGETC - In Harvard architectures, data accesses and + instruction accesses occur on different busses, perhaps + concurrently. All data accesses are performed on the data bus + unless special machine instructions are used to read data + from the instruction address space. Also, in the typical + MCU, the available SRAM data memory is much smaller that the + non-volatile FLASH instruction memory. So if the application + requires many constant strings, the only practical solution may + be to store those constant strings in FLASH memory where they + can only be accessed using architecture-specific machine + instructions. + + If CONFIG_ARCH_ROMGETC is defined, then the architecture logic + must export the function up_romgetc(). up_romgetc() will simply + read one byte of data from the instruction space. + + If CONFIG_ARCH_ROMGETC, certain C stdio functions are effected: + (1) All format strings in printf, fprintf, sprintf, etc. are + assumed to lie in FLASH (string arguments for %s are still assumed + to reside in SRAM). And (2), the string argument to puts and fputs + is assumed to reside in FLASH. Clearly, these assumptions may have + to modified for the particular needs of your environment. There + is no "one-size-fits-all" solution for this problem. Sizes of configurable things (0 disables) |