Assembler CH32V307x.

[AVI-crak]

Hello.
I'm a little mocking CH32V307VCT6. The C code works without problems, but I want a lower level - assembler. And here is a complete failure. All my ARM developments turned out to be useless.
First, I want to deal with the startup file startup_ch32v30x_D8C.s .
The line "NMI_Handler: 1: j 1b" and below is of interest - I have not seen such a syntax, and I do not understand the purpose of the line.

Code: [Select]

.....
    .weak   DMA2_Channel9_IRQHandler   /* DMA2 Channel 9 */
    .weak   DMA2_Channel10_IRQHandler  /* DMA2 Channel 10 */
    .weak   DMA2_Channel11_IRQHandler  /* DMA2 Channel 11 */

NMI_Handler:  1:  j 1b
HardFault_Handler:  1:  j 1b
Ecall_M_Mode_Handler:  1:  j 1b
Ecall_U_Mode_Handler:  1:  j 1b
Break_Point_Handler:  1:  j 1b
.....

[langwadt]

1 minute of google; "J" is jump, "1b" is 1 backwards, so it is an infinite loop

[brucehoult]

This is absolutely standard GNU assembler on any platform, including ARM. "1b" for the nearest label 1 in a backwards direction, "1f" for the nearest label 1 in a forwards direction.

And RISC-V uses "J" for the unconditional Jump instruction (short for JAL with return address discarded into register 0) vs ARM using B/BL for the same purpose (ARM originally of course could make any instruction conditional, so no distinction possible between conditional Branch and unconditional Jump).

[AVI-crak]

It is clear - these are traps for a stupid code, literally.
The standard GCC uses a more cunning thing - a name replacement. And this seems to me a more logical solution.

Code: [Select]

  .weak      NMI_Handler
  .thumb_set NMI_Handler,Default_Handler

  .weak      HardFault_Handler
  .thumb_set HardFault_Handler,Default_Handler

[brucehoult]

It is clear - these are traps for a stupid code, literally.
The standard GCC uses a more cunning thing - a name replacement. And this seems to me a more logical solution.

Code: [Select]

  .weak      NMI_Handler
  .thumb_set NMI_Handler,Default_Handler

  .weak      HardFault_Handler
  .thumb_set HardFault_Handler,Default_Handler

It's exactly the same. Look at the .weak definitions above.

The difference is that this code has a different default handler for each trap type, not just the same one for all. So if your chip locks up and you connect with a debugger you can see WHICH loop it is stuck in and therefore which kind of trap that can't happen actually did happen and you should add a handler for it.

At a cost of 2 bytes of code each.