USART IO over direct USB

[brycelelbach]

Using the USART output code doesn't work for over direct USB (I've tried catting the serial port on Windows, and looking at the output window in EasyC). I might be doing something wrong (please tell me if I am) - I'm using usart_puts.

It'd be really awesome if we had a way to communicate with our laptops/desktops. I'm not sure if this is possible, and I can't find anything on the wiki with more info about this.

tl;dr - Can I send/receive data to my laptop from the Cortex using only a direct USB connection? If so, how can we do this? This would be very awesome.

[brycelelbach]

More thoughts: I know that this is /possible/, at least, because easyC does it. They have a few archives in their installation that have the code for this. Shoot me an email - blelbach at cct dot lsu dot edu - for more details

[brycelelbach]

Hm.... in vex_hw.h (in arch_cortex), line 113, we have the flag enable_printfs. I wonder if setting htis would do the trick?

[brycelelbach]

Well, setting that bit gives me some IO. Now, after I've flashed the device, if I cat the serial terminal, I get data (although it's garbled). I don't get any output though if I turn the device on after flashing or if I unplug it and plug it back in.

While the data is garbled, I confirmed it was the actual printfs from the device by compiling/flashed first with code that just called usart1_putc() in a loop with the same char each time, and then I compiled and flashed with code that did usart1_puts() with a two-character string. The first output contained a stream of a single character, and the second output contained alternating characters. However, in both cases, the wrong characters were printed.

Any thoughts on why it only works when plugged in and powered off?

[brycelelbach]

The easyC documentation page for their terminal window indicates that when the robot is powered on, you need to press the refresh button on their GUI to get print statements to show up. I'm guessing we need to do something similiar. They say the reason is that the Wifi code needs to be in debug mode (or something like that).

[brycelelbach]

When I do usart1_putc(42), I get 0x9886 in the output. When I do usart1_putc(43), I get 0x9e86 in the output.

[brycelelbach]

BTW, for reference, I turned on enable_printfs by modifying spi_packet_init_u2m as follows:

void spi_packet_init_u2m(spi_packet_u2m_t *u2m)
{
    u2m->sync = SYNC_MAGIC;
    u2m->version = 1;
    u2m->packet_num = 0;

    // First send needs to be "config"
    u2m->state.a = STATE_CONFIG;
    u2m->sys_flags.b.auton = 1;
    u2m->sys_flags.b.enable_printfs = 1;

    uint8_t i;
    for(i = 0; i < MOTOR_CT; i++) {
        u2m->motors[i] = 127;
    }
}

[brycelelbach]

In the Vex2.0_Source zip, the ddt_support.c file looks promising