[PATCH 1/1] clk: kendryte/pll.h: do not redefine nop()

Sean Anderson seanga2 at gmail.com
Wed Aug 5 13:45:54 CEST 2020

On 8/3/20 2:20 PM, Heinrich Schuchardt wrote:
> On 03.08.20 16:08, Sean Anderson wrote:
>> Maybe. Because we are configuring the PLL, the CPU clock is temporarily
>> set to the in0 oscillator, so the timer would give an incorrect delay.
>> However, it would probably be fine even if incorrect.  The original
>> reason I used nops is because that is what the SDK does in its PLL
>> configuration function [1]. I believe I tried using udelay at one point,
>> but I don't remember whether I had any issues with it.
>> --Sean
>> [1] https://github.com/kendryte/kendryte-standalone-sdk/blob/develop/lib/drivers/sysctl.c#L844
> This is what udelay(1) gets compiled to:
> 000000000000004a <.LBE106>:
>         udelay(1);
>   4a:   4505                    li      a0,1
> 000000000000004c <.LVL21>:
>   4c:   00000097                auipc   ra,0x0
>   50:   000080e7                jalr    ra # 4c <.LVL21>
> Somehow udelay() seems not to be fully implemented and the platform. So
> I think we should stay with the nop() macro.

Hm, I don't see this generated code. What function is that a disassembly

$ riscv64-linux-gnu-objdump -S --disassemble=__udelay u-boot

u-boot:     file format elf64-littleriscv

Disassembly of section .text:

Disassembly of section .text_rest:

00000000800197f8 <__udelay>:
	do_div(tick, 1000000);
	return tick;

void __weak __udelay(unsigned long usec)
    800197f8:	1101                	addi	sp,sp,-32
    800197fa:	ec06                	sd	ra,24(sp)
    800197fc:	e822                	sd	s0,16(sp)
    800197fe:	e426                	sd	s1,8(sp)
    80019800:	84aa                	mv	s1,a0
	uint64_t tmp;

	tmp = get_ticks() + usec_to_tick(usec);	/* get current timestamp */
    80019802:	f7bff0ef          	jal	ra,8001977c <get_ticks>
    80019806:	842a                	mv	s0,a0
    80019808:	8526                	mv	a0,s1
    8001980a:	fcbff0ef          	jal	ra,800197d4 <usec_to_tick>
    8001980e:	942a                	add	s0,s0,a0

	while (get_ticks() < tmp+1)	/* loop till event */
    80019810:	0405                	addi	s0,s0,1
    80019812:	f6bff0ef          	jal	ra,8001977c <get_ticks>
    80019816:	fe856ee3          	bltu	a0,s0,80019812 <__udelay+0x1a>
    8001981a:	60e2                	ld	ra,24(sp)
    8001981c:	6442                	ld	s0,16(sp)
    8001981e:	64a2                	ld	s1,8(sp)
    80019820:	6105                	addi	sp,sp,32
    80019822:	8082                	ret


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