Broadcom LV mode

This is an undocumented special JTAG mode used on some Broadcom SoCs.

Key properties

 * IR length is 32 bits
 * Some hints available at hndjtagdefs.h
 * IDCODE command is 0xfffffffe

Known IDCODEs

 * 0xa817f
 * 0x1471617f
 * 0x1535717f
 * 0x1535617f
 * 0xc417f

Switch to EJTAG
It's possible to switch to standard EJTAG by doing the following:
 * Shift 0x0143ff3a into IR, end state run/idle
 * Shift 1 into DR (length 32), end state run/idle
 * Reenumerate the bus, the device will reappear with a different ID and IR length (5 or 7)

OpenOCD example:  poll 0 irscan $_CHIPNAME-lv.tap 0x143ff3a drscan $_CHIPNAME-lv.tap 32 1 