fix incorrect rx buf in cdc

[hathach]

Describe the PR
This typo exists a long time ago, and it is a total mystery why tinyusb does not crash and works flawlessly so far !!

[dhalbert]

I compiled CircuitPython with p_cdc->epout_buf and with &p_cdc->epout_buf, and the resulting .elf and .asm's are identical.

This is a peculiarity of references to C arrays: https://stackoverflow.com/questions/2528318/how-come-an-arrays-address-is-equal-to-its-value-in-c.

So though it's a little "wrong", adding the & doesn't do anything.

There's a demo program in the link above, and here's one I wrote before finding that:

#include <stdio.h>

typedef struct {
    char buf[2];
} s_t;

int main() {
    s_t s;
    s_t *sp = &s;

    void *p1 = sp->buf;
    void *p2 = &sp->buf;

    printf("p1: %p, p2: %p\n", p1, p2);
}

$ ./a.out
p1: 0x7ffcc06db176, p2: 0x7ffcc06db176

[hathach]

thank you @dhalbert for looking deeper and detail explanation. Luckily array and &array` have the same value, C is really a mystery language :D

[RichardSWheatley]

Yes, I am familiar with C and pointers. What I have noticed is that when changes are made, there aren’t a lot of comments as to what was changed and why.

Was hoping to however made the change would put those comments here.

I use tinyusb and most of the changes that I see do not have consequences for usability.

[hathach]

I don't understand your point. This is bug/typo and as mentioned, it should crash previously in my opinion but it doesn't (pure luck). The code speaks for itself, what else I should put the comment for ?

I use tinyusb and most of the changes that I see do not have consequences for usability.

Then don't upgrade if you have no need for those changes.