Starterware/PROCESSOR-SDK-AM437X: DCAN_IF1CMD register question

Tool/software: Starterware

Hi，

We're debugging Dcan peripherals（AM4377），and have some questions about registers related.

1. I don't understand the the function of bit of CTRL（DCAN_IF1CMD），and the relationship with bit TXRQST_NEWDAT（DCAN_IF1CMD）.

2. How can I trigger the transmit of the massage？writes the message number to bits [7:0] of the IF1 command register？or set the bit TXRQST_NEWDAT？

Thanks