What is it the strange CPU instruction generated by SDCC?

[Vyacheslav Azarov]

Hello everyone.

SLCC generated a strange instruction similar to JRF, represented as .byte 0x21 pseudo-instruction. Can anyone explain what this is? A code snippet is provided in the attachment. The compiler options are as follows: -mstm8 --out-fmt-elf --opt-code-speed --max-allocs-per-node 6900 - -stack-auto -c

Thanks in advance.

[Tesla DeLorean]

Just causes it to EAT the next byte/instruction. JRF (Jump if FALSE, ie NEVER) will take the next byte as the intended target, which it never acts upon. Think of it as the first byte of a two byte NOP, equivalent in this situation to a JRA 00106$ without the pipeline hit, and uses less code

478 ;	-----------------------------------------
                                    479 ;	 function USART1_RX_TIM5_CC_IRQHandler
                                    480 ;	-----------------------------------------
      00011F                        481 _USART1_RX_TIM5_CC_IRQHandler:
      00011F 4F               [ 1]  482 	clr	a
      000120 62               [ 2]  483 	div	x, a
                                    484 ;	/home/master/workspace/_myrtos-newview-0.0.0/SPL/stm8l15x_tim5.h: 1996: tim5_flag_l = (uint8_t)(TIM5->SR1 & (uint8_t)(TIM5_FLAG));
      000121 C6 53 06         [ 1]  485 	ld	a, 0x5306
      000124 A4 04            [ 1]  486 	and	a, #0x04
      000126 97               [ 1]  487 	ld	xl, a
                                    488 ;	/home/master/workspace/_myrtos-newview-0.0.0/SPL/stm8l15x_tim5.h: 1997: tim5_flag_h = (uint8_t)(TIM5->SR2 & (uint8_t)((uint16_t)TIM5_FLAG >> 8));
      000127 C6 53 07         [ 1]  489 	ld	a, 0x5307
                                    490 ;	/home/master/workspace/_myrtos-newview-0.0.0/SPL/stm8l15x_tim5.h: 1999: if ((uint8_t)(tim5_flag_l | tim5_flag_h) != 0)
      00012A 9F               [ 1]  491 	ld	a, xl
      00012B 4D               [ 1]  492 	tnz	a
      00012C 27 03            [ 1]  493 	jreq	00105$
                                    494 ;	/home/master/workspace/_myrtos-newview-0.0.0/SPL/stm8l15x_tim5.h: 2001: bitstatus = SET;
      00012E A6 01            [ 1]  495 	ld	a, #0x01
                                    496 ;	/home/master/workspace/_myrtos-newview-0.0.0/SPL/stm8l15x_tim5.h: 2005: bitstatus = RESET;
      000130 21                     497 	.byte 0x21
      000131                        498 00105$:
      000131 4F               [ 1]  499 	clr	a
      000132                        500 00106$:
                                    501 ;	../stm8l15x_it.c: 363: if (TIM5_GetFlagStatus(TIM5_FLAG_CC2) == SET) os_yield();
      000132 4A               [ 1]  502 	dec	a
      000133 26 05            [ 1]  503 	jrne	00102$
      000135 CDr00r00         [ 4]  504 	call	_os_yield
      000138 20 06            [ 2]  505 	jra	00108$
      00013A                        506 00102$:
                                    507 ;	../stm8l15x_it.c: 365: os_handle_interrupt_error(28);
      00013A 4B 1C            [ 1]  508 	push	#0x1c
      00013C CDr00r00         [ 4]  509 	call	_os_handle_interrupt_error
      00013F 84               [ 1]  510 	pop	a
      000140                        511 00108$:
                                    512 ;	../stm8l15x_it.c: 366: }
      000140 80               [11]  513 	iret

[Vyacheslav Azarov]

Super skip! Very original, as well as bypassing the error of the first division. Thank you very much.