jtag_ring_length
len = jtag_ring_length(jreg, ring);
len = jtag_ring_length(jreg, ring | (i + 1));
len = jtag_ring_length(jreg, ring | 1);
len = jtag_ring_length(jreg, ring | 1);
static int jtag_ring_length(volatile u_int *, jtag_ring);