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Re: [avr-libc-dev] Is eeprom_write_byte supporting the new bitwise eepro
Re: [avr-libc-dev] Is eeprom_write_byte supporting the new bitwise eeprom write feature of new devices?
Thu, 13 Apr 2006 09:52:51 +0200
Selbst wrote on Mittwoch, 12. April 2006 23:43 :
> i just read about the more or less new feature of the newer avr devices
> that allows more efficient eeprom write operations. Basically it allows to
> save some erase cycles if bits only need to be set but none erased:
> Are the current avr-libc functions using this eeprom write scheme if
To my best knowledge there is no such implementation so far.
IMO, there will always be a trade-off. The present library code is optimized
for *size*: When I re-wrote the EEPROM functions that what I had in mind
first of all was the code efficiency. I.e. I made quite some efforts to limit
code size by being as register efficient as possible and as code efficient as
possible. Speed was not a focus at all. It was frequently stated opinion IIRC
that EEPROM functions that are trying to be as fast as possible should be
rather left to the user: It's probably likely that one needs knowledge on
some of the system's properties to be *really* fast, e.g. by IRQs.
What I'd like to suggest you to do in order to implement your whishes quite
1.) Add an own assembly file to your avr project that is supposed to hold your
own "fast" eeprom write byte function.
2.) Re-Define the eeprom write byte function. No change elsewhere will be
necessary. The function entry label should read "__eeprom_write_byte_1C1D1E"
or "__eeprom_write_byte_1F2021" depending on the place where your device has
it's eeprom registers. The linker then will use your definitions of the
function instead of the library's own one. You will only have to implement
the write byte functions: The write block function and the write word
function themself make use of the write byte function and would benefit of
You should keep care to make the linker place the function in the .text.eeprom
section just like the present library function.
Note that for the eeprom functions the usual calling convention for functions
does not apply! You will have to preserve all of the registers. We are not
using the standard calling convention in order to be as code efficient as
... hope that helps,
Here is the present implementation. Note that your function also will be
required to implement the auto-increment feature for r26:r27. EEprom write
block and eeprom write byte rely on this. The _EELABEL makro adds the suffix
(e.g. 1C1D1E) that I mentioned above.
/* write a byte to EEPROM
Address in r26:r27, value in __tmp_reg__
Post increment r26:r27. */
.section .text.eeprom, "ax", @progbits
sbic _SFR_IO_ADDR(EECR), EEWE
rjmp _EELABEL(eeprom_write_byte) /* make sure EEPROM is ready
out _SFR_IO_ADDR(EEARH), r27
out _SFR_IO_ADDR(EEARL), r26
adiw r26,1 /* Increment x register */
in __tmp_reg__, _SFR_IO_ADDR(SREG)
cli ; /* no ints between setting EEMWE and EEWE */
sbi _SFR_IO_ADDR(EECR), EEMWE
sbi _SFR_IO_ADDR(EECR), EEWE
out _SFR_IO_ADDR(SREG), __tmp_reg__