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Add support for accessing printf, sprintf, puts, etc. strings that do not lie in the MCU data space

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git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@3738 42af7a65-404d-4744-a932-0658087f49c3
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patacongo 2011-07-01 19:08:04 +00:00
parent dd615c2b19
commit 26c25b1057
1 changed files with 44 additions and 13 deletions
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57
Documentation/NuttxPortingGuide.html
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@ -12,7 +12,7 @@
<h1><big><font color="#3c34ec">
<i>NuttX RTOS Porting Guide</i>
</font></big></h1>
<p>Last Updated: June 18, 2011</p>
<p>Last Updated: July 1, 2011</p>
</td>
</tr>
</table>
@ -3628,34 +3628,65 @@ build
<ul>
<li>
<code>CONFIG_NOPRINTF_FIELDWIDTH</code>: sprintf-related logic is a
<code>CONFIG_NOPRINTF_FIELDWIDTH</code>: <code>sprintf</code>-related logic is a
little smaller if we do not support fieldwidthes
</li>
<li>
<code>CONFIG_LIBC_FLOATINGPOINT</code>: By default, floating point
support in printf, sscanf, etc. is disabled.
support in <code>printf</code>, <code>sscanf</code>, etc. is disabled.
</li>
</ul>
<h2>Allow for architecture optimized implementations</h2>
<p>
The architecture can provide optimized versions of the following to improve system performance.
</p>
<ul>
<p>
<li>
The architecture can provide optimized versions of the following to improve system performance.
</li>
<ul><p>
<code>CONFIG_ARCH_MEMCPY</code>, <code>CONFIG_ARCH_MEMCMP</code>, <code>CONFIG_ARCH_MEMMOVE</code>,
<code>CONFIG_ARCH_MEMSET</code>, <code>CONFIG_ARCH_STRCMP</code>, <code>CONFIG_ARCH_STRCPY</code>,
<code>CONFIG_ARCH_STRNCPY</code>, <code>CONFIG_ARCH_STRLEN</code>, <code>CONFIG_ARCH_STRNLEN</code>,
<code>CONFIG_ARCH_BZERO</code>
</p>
<p>
</p></ul>
<li>
The architecture may provide custom versions of certain standard header files:
</p>
<p>
</li>
<ul><p>
<code>CONFIG_ARCH_MATH_H</code>, <code>CONFIG_ARCH_STDBOOL_H</code>, <code>CONFIG_ARCH_STDINT_H</code>
</p>
</p></ul>
<li>
<p><code>CONFIG_ARCH_ROMGETC</code>:
There are cases where string data cannot be cannot be accessed by simply de-referencing a string pointer.
As examples:
</p>
<ul>
<li>
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.
</li>
<li>
A similar case is where strings are retained in &quot;external&quot; memory such as EEPROM or serial FLASH.
This case is similar only in that again special operations are required to obtain the string data;
it cannot be accessed directly from a string pointer.
</li>
</ul>
<p>
If <code>CONFIG_ARCH_ROMGETC</code> is defined, then the architecture-specific logic must export the function <code>up_romgetc()</code>.
<code>up_romgetc()</code> will simply read one byte of data from the instruction space.
</p>
<p>
If <code>CONFIG_ARCH_ROMGETC</code>, certain C stdio functions are effected:
(1) All format strings in <code>printf</code>, <code>fprintf</code>, <code>sprintf</code>, etc. are assumed to lie in FLASH
(string arguments for <code>%s</code> are still assumed to reside in SRAM).
And (2), the string argument to <code>puts</code> and <code>fputs</code> is assumed to reside in FLASH.
Clearly, these assumptions may have to modified for the particular needs of your environment.
There is no &quot;one-size-fits-all&quot; solution for this problem.
</p>
</ul>
<h2>Sizes of configurable things (0 disables)</h2>