[help] K210 serial port has no output

i make the fw_payload.bin
make CROSS_COMPILE=riscv64-unknown-elf- PLATFORM=kendryte/k210 PLATFORM_RISCV_XLEN=64
CC lib/sbi/riscv_asm.o
CC lib/sbi/riscv_atomic.o
AS lib/sbi/riscv_hardfp.o
CC lib/sbi/riscv_locks.o
CC lib/sbi/sbi_ecall.o
CC lib/sbi/sbi_ecall_exts.o
CC lib/sbi/sbi_ecall_time.o
CC lib/sbi/sbi_ecall_rfence.o
CC lib/sbi/sbi_ecall_ipi.o
CC lib/sbi/sbi_ecall_base.o
CC lib/sbi/sbi_ecall_hsm.o
CC lib/sbi/sbi_ecall_srst.o
CC lib/sbi/sbi_ecall_susp.o
CC lib/sbi/sbi_ecall_pmu.o
CC lib/sbi/sbi_ecall_dbcn.o
CC lib/sbi/sbi_ecall_cppc.o
CC lib/sbi/sbi_ecall_legacy.o
CC lib/sbi/sbi_ecall_vendor.o
CC lib/sbi/sbi_ecall_dbtr.o
CC lib/sbi/sbi_bitmap.o
CC lib/sbi/sbi_bitops.o
CC lib/sbi/sbi_console.o
CC lib/sbi/sbi_domain_context.o
CC lib/sbi/sbi_domain.o
CC lib/sbi/sbi_emulate_csr.o
CC lib/sbi/sbi_fifo.o
CC lib/sbi/sbi_hart.o
CC lib/sbi/sbi_heap.o
CC lib/sbi/sbi_math.o
AS lib/sbi/sbi_hfence.o
CC lib/sbi/sbi_hsm.o
CC lib/sbi/sbi_illegal_insn.o
CC lib/sbi/sbi_init.o
CC lib/sbi/sbi_ipi.o
CC lib/sbi/sbi_irqchip.o
CC lib/sbi/sbi_platform.o
CC lib/sbi/sbi_pmu.o
CC lib/sbi/sbi_dbtr.o
CC lib/sbi/sbi_scratch.o
CC lib/sbi/sbi_string.o
CC lib/sbi/sbi_system.o
CC lib/sbi/sbi_timer.o
CC lib/sbi/sbi_tlb.o
CC lib/sbi/sbi_trap.o
CC lib/sbi/sbi_trap_ldst.o
CC lib/sbi/sbi_unpriv.o
AS lib/sbi/sbi_expected_trap.o
CC lib/sbi/sbi_cppc.o
AR lib/libsbi.a
CC platform/kendryte/k210/lib/utils/timer/aclint_mtimer.o
CC platform/kendryte/k210/lib/utils/timer/fdt_timer.o
CC platform/kendryte/k210/lib/utils/timer/fdt_timer_drivers.o
CC platform/kendryte/k210/lib/utils/serial/sifive-uart.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_addresses.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_check.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_empty_tree.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_ro.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_rw.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_strerror.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_sw.o
CC platform/kendryte/k210/lib/utils/libfdt/fdt_wip.o
CC platform/kendryte/k210/lib/utils/irqchip/plic.o
CC platform/kendryte/k210/lib/utils/ipi/aclint_mswi.o
CC platform/kendryte/k210/lib/utils/fdt/fdt_helper.o
CC platform/kendryte/k210/lib/utils/fdt/fdt_fixup.o
CC platform/kendryte/k210/platform.o
CC platform/kendryte/k210/k210.o
AR platform/kendryte/k210/lib/libplatsbi.a
AS platform/kendryte/k210/firmware/payloads/test_head.o
CC platform/kendryte/k210/firmware/payloads/test_main.o
MERGE platform/kendryte/k210/firmware/payloads/test.o
ELF platform/kendryte/k210/firmware/payloads/test.elf
OBJCOPY platform/kendryte/k210/firmware/payloads/test.bin
AS platform/kendryte/k210/firmware/fw_payload.o
ELF platform/kendryte/k210/firmware/fw_payload.elf
OBJCOPY platform/kendryte/k210/firmware/fw_payload.bin

and then
sudo python3 ~/xv6-k210/tools/kflash.py -p /dev/ttyUSB0 -b 1500000 -t build/platform/kendryte/k210/firmware/fw_payload.bin

[INFO] COM Port Selected Manually: /dev/ttyUSB0
[INFO] Default baudrate is 115200 , later it may be changed to the value you set.
[INFO] Trying to Enter the ISP Mode...
._
[INFO] Automatically detected goE/kd233

[INFO] Greeting Message Detected, Start Downloading ISP
Downloading ISP: |==============================================================================| 100.0% 10kiB/s
[INFO] Booting From 0x80000000
[INFO] Wait For 0.1 second for ISP to Boot
[INFO] Boot to Flashmode Successfully
[INFO] Selected Baudrate: 1500000
[INFO] Baudrate changed, greeting with ISP again ...
[INFO] Boot to Flashmode Successfully
[INFO] Selected Flash: On-Board
[INFO] Initialization flash Successfully
Programming BIN: |==============================================================================| 100.0% 25kiB/s
[INFO] Rebooting...
--- forcing DTR inactive
--- forcing RTS inactive
--- Miniterm on /dev/ttyUSB0 115200,8,N,1 ---
--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---

This problem has been bothering me for a long time. Thank you for your help

Start with platform/kendryte/k210/lib/utils/serial/sifive-uart.c and the K210 platform files named in the build output, then review the kflash.py invocation and the serial-terminal settings. Reproduce the flash and reboot process, and verify that the K210 produces the expected serial output after programming fw_payload.bin.