[avr-gcc-list] In-line Assembler Code

[Alistair Gadd]

Hi Guys,

I'm trying to use GCC-AVR to set up the clock prescale on an ATmega32U4, using the clock_prescale_set() function as outlined in the "avr/power.h " header file.

If I call:
    clock_prescale_set(clock_div_1)
or
    clock_prescale_set(0);
where clock_prescale_set is defined in "avr/power.h" as follows:

typedef enum
{
    clock_div_1 = 0,
    clock_div_2 = 1,
    clock_div_4 = 2,
    clock_div_8 = 3,
    clock_div_16 = 4,
    clock_div_32 = 5,
    clock_div_64 = 6,
    clock_div_128 = 7,
    clock_div_256 = 8
#if defined(__AVR_ATmega128RFA1__) \
|| defined(__AVR_ATmega256RFR2__) \
|| defined(__AVR_ATmega2564RFR2__) \
|| defined(__AVR_ATmega128RFR2__) \
|| defined(__AVR_ATmega1284RFR2__) \
|| defined(__AVR_ATmega64RFR2__) \
|| defined(__AVR_ATmega644RFR2__)
    , clock_div_1_rc = 15
#endif
} clock_div_t;

void clock_prescale_set(clock_div_t __x)
{
    uint8_t __tmp = _BV(CLKPCE);
    __asm__ __volatile__ (
        "in __tmp_reg__,__SREG__" "\n\t"
        "cli" "\n\t"
        "sts %1, %0" "\n\t"
        "sts %1, %2" "\n\t"
        "out __SREG__, __tmp_reg__"
        : /* no outputs */
        : "d" (__tmp),
          "M" (_SFR_MEM_ADDR(CLKPR)),
          "d" (__x)
        : "r0");
}

I get the following in-line assembler generated (.lss file extract):

void clock_prescale_set(clock_div_t __x)
{
    uint8_t __tmp = _BV(CLKPCE);
    __asm__ __volatile__ (
     12a:    90 e0           ldi    r25, 0x00    ; 0
     12c:    80 e8           ldi    r24, 0x80    ; 128
     12e:    0f b6           in    r0, 0x3f    ; 63
     130:    f8 94           cli
     132:    80 93 61 00     sts    0x0061, r24
     136:    90 93 61 00     sts    0x0061, r25
     13a:    0f be           out    0x3f, r0    ; 63

which I can understand, but if I call:
    clock_prescale_set(clock_div_4);
or:
    clock_prescale_set(2);
I get exactly the same code generated, in other words:

void clock_prescale_set(clock_div_t __x)
{
    uint8_t __tmp = _BV(CLKPCE);
    __asm__ __volatile__ (
     12a:    90 e0           ldi    r25, 0x00    ; 0
     12c:    80 e8           ldi    r24, 0x80    ; 128
     12e:    0f b6           in    r0, 0x3f    ; 63
     130:    f8 94           cli
     132:    80 93 61 00     sts    0x0061, r24
     136:    90 93 61 00     sts    0x0061, r25
     13a:    0f be           out    0x3f, r0    ; 63

where I would expect to get this:

void clock_prescale_set(clock_div_t __x)
{
    uint8_t __tmp = _BV(CLKPCE);
    __asm__ __volatile__ (
     12a:    90 e0           ldi    r25, 0x02    ; 0
     12c:    80 e8           ldi    r24, 0x80    ; 128
     12e:    0f b6           in    r0, 0x3f    ; 63
     130:    f8 94           cli
     132:    80 93 61 00     sts    0x0061, r24
     136:    90 93 61 00     sts    0x0061, r25
     13a:    0f be           out    0x3f, r0    ; 63

I don't get any compilation errors, so I think it sees the enum okay and the assembly listing is fresh each time I try. I'm sure I must be doing something simplisticly crazy, but I think I need help, because this is driving me nuts and it's been a long day. I'm used to using separate assembler files and I'm not a great boffin on using in-line assembly, but I really think I need to get a collar on it.

Many thanks to whoever can help, best regards,
Alistair.

PS: My tool set versions are as follows::

Atmel Studio 6 (Version: 6.2.1153 - )
© 2014 Atmel Corp.
All rights reserved.


OS Version: Microsoft Windows NT 5.2.3790 Service Pack 2
Platform: Win32NT


Installed Packages: Shell VSIX manifest - 6.2
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Company: Atmel Corporation


Installed Packages: Atmel ARM GNU Toolchain - 4.8.3.1429
ARM Toolchain
Version: ARM_Toolchain_Version:4.8.3.277 GCC_VERSION:4.8.3
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Company: Atmel
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Version: 3.20
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Company: Atmel
HelpUrl:
Release Description: ARM Support File Version



Installed Packages: AVR macro Assembler - 2.1.39.1117
AVR Assembler
Version: 2.1.39.232
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Company: Atmel
HelpUrl:
Release Description: AVR Assembler For 8-Bit Devices



Installed Packages: Atmel AVR (32 bit) GNU Toolchain - 3.4.2.1057
AVR Toolchain 32
Version: AVR32_Toolchain_Version:3.4.2.435 GCC_VERSION:4.4.7
Package GUID: DB6D383F-C5D9-4E7E-BBF9-F37C6EEB59FD
Company: Atmel
HelpUrl:
Release Description: AVR Toolchain For 32-Bit Devices



Installed Packages: Atmel AVR (8 bit) GNU Toolchain - 3.4.4.1056
AVR Toolchain 8 Bit
Version: AVR8_Toolchain_Version:3.4.4.1229 GCC_VERSION:4.8.1
Package GUID: 2C7AA7CF-94C6-463C-81DA-4AA03B613C3B
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ASF
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HelpUrl: http://asf.atmel.com/3.18.0
Release Description: ASF - 3.18.0 Release

ASF
Version: 3.17.0
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ASF
Version: 3.16.0
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HelpUrl: http://asf.atmel.com/3.16.0
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ASF
Version: 3.15.0
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HelpUrl: http://asf.atmel.com/3.15.0
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ASF
Version: 3.14.0
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HelpUrl: http://asf.atmel.com/3.14.0
Release Description: ASF - 3.14.0 Release

ASF
Version: 3.13.1
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Company: Atmel
HelpUrl: http://asf.atmel.com/3.13.1
Release Description: ASF - 3.13.1 Release

ASF
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Release Description: ASF - 3.12.1 Release

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Version: 3.11.0
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HelpUrl: http://asf.atmel.com/3.11.0
Release Description: ASF - 3.11.0 Release

ASF
Version: 3.10.1
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Company: Atmel
HelpUrl: http://asf.atmel.com/3.10.1
Release Description: ASF - 3.10.1 Release



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Version: 6.2.666
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GdbConsole
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Company: Atmel