Not sure where to put this, and the FreeBSD devs probably already saw it, but I thought I'd post it here anyway in case it's useful for creating drivers for this.
Exploiting Broadcom’s Wi-Fi Stack
Exploiting Broadcom’s Wi-Fi Stack
Cypress has recently acquired Broadcom’s Wireless IOT business, and have published many of the datasheets related to Broadcom’s Wi-Fi chipsets (albeit for a slightly older SoC, the BCM4339). Reading through the datasheet, we gain some insight into the hardware architecture behind the Wi-Fi chipset.