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Re: [avr-libc-dev] [patch #6718] Optimize the EEPROM functions

From: Bob Paddock
Subject: Re: [avr-libc-dev] [patch #6718] Optimize the EEPROM functions
Date: Fri, 24 Jul 2009 11:46:46 -0400

>  * The XMEGA is realized.

> At this moment the XMEGA is not tested.

I do not understand this code in eewr_byte.S.

The 'read' command is being issued to the XMega NVM
in the write function?  Don't all XMega EEPROM writes have to be
done via the page buffer?

ENTRY   eeprom_write_byte
        mov     r18, r22

ENTRY   eeprom_write_r18

#if  __AVR_XMEGA__      /* -------------------------------------------- */

# ifndef CCP_IOREG_gc
#  define CCP_IOREG_gc  0xD8    /* IO Register Protection       */
# endif
#  define NVM_CMD_READ_EEPROM_gc        0x06
# endif

  ; Prepare base address of NVM.
        ldi     ZL, lo8(NVM_BASE)
        ldi     ZH, hi8(NVM_BASE)

  ; Wait until NVM is not busy.
1:      ldd     r19, Z + NVM_STATUS - NVM_BASE
        sbrc    r19, NVM_NVMBUSY_bp
        rjmp    1b

  ; Desable EEPROM mapping into data space.
        ldd     r19, Z + NVM_CTRLB - NVM_BASE
        andi    r19, ~NVM_EEMAPEN_bm
        std     Z + NVM_CTRLB - NVM_BASE, XL

  ; Set address and data to write to.
        std     Z + NVM_ADDR0 - NVM_BASE, addr_lo
        std     Z + NVM_ADDR1 - NVM_BASE, addr_hi
        std     Z + NVM_ADDR2 - NVM_BASE, __zero_reg__
        std     Z + NVM_DATA0 - NVM_BASE, r18

  ; Issue EEPROM read command.
        ldi     r18, NVM_CMD_READ_EEPROM_gc
        std     Z + NVM_CMD - NVM_BASE, r18
        ldi     r18, CCP_IOREG_gc
        ldi     r19, NVM_CMDEX_bm
        out     CCP, r18
        std     Z + NVM_CTRLA - NVM_BASE, r19

  ; Increment address.
        adiw    addr_lo, 1


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