Things to know

Project and AVR Studio

• Assembler files are .S files
• You can mix .c ans .S files in the programe, no problem
• Your .c files gets interpreted as pseudo assembler file in the .??? file of your solution. Nice to see what your code becomes and where is the error coming from.

ASM : jmp, call, and flow control

• The rjmp/jmp, rcall/call, ... is that the r-version work for "close" addresses and the non-r version for the long jumps, and are not implmented on small uC (like tiny2313)
  • Simple trick : code everything with a rjmp and rcall, the compiler will tell you if you need to use the long-range version.
• jmp just change the Stack Pointer, call is a subroutine call that and you return to previous location%201 using ret

Registers

• Affect a register to a variable (uint8_t) with register volatile uint8_t variable01 asm("r2");
  • Reserved to r2 .. r7
• r0 is always free temp variable
• r1 should be always 0, so reset after use (clr r1) or just avoid
• r18-r27, r30-r31 are used when mixing C and ASM so save them before
• r2-r17, r28-r29 are not used for callign C so just mind your ASM and push/pop if needed
• Detailed registers explanation : http://www.gnu.org/savannah-checkouts/non-gnu/avr-libc/user-manual/FAQ.html#faq_reg_usage

Playing with memory

Read and Write in SRAM

The key commands are LD... and ST..., with variants if you use the address register X or Y.

• Very good http://www.avr-asm-tutorial.net/avr_en/beginner/SRAM.html
• A sample, much less clear however http://www.attiny.com/scroll3.htm

Links

General AVR ASM tutorials

• Very good http://www.avrbeginners.net/
• Another special ASM http://www.avr-asm-tutorial.net/
• AVR Tutorials http://www.avr-tutorials.com/
• General talk about AVR Studio http://avrstudio5.wordpress.com/
• Again tutorials http://www.attiny.com/index.htm

Mixing C and ASM

• Adding inline asm("") http://www.nongnu.org/avr-libc/user-manual/inline_asm.html
• Combining .c and .S files http://www.nongnu.org/avr-libc/user-manual/group__asmdemo.html
  • Another sample http://dics.voicecontrol.ro/process_mails/arata_discutia/124981/Mixed_C_and_assembly_with_AVR_studio_and_gcc.html
• http://www.scriptoriumdesigns.com/embedded/interrupt_examples.php