VBASE
case '\f': bzero((void *)VBASE, 80*25*2); d_pos = 0; break;
((u_int16_t volatile *)VBASE)[d_pos++] = 0x0700 | (u_char)c;
#define CKPT(c) (*(u_short volatile *)(VBASE+160) = (0x1700 | (c)))