(config! {:address 0x8000})
(const! mmio-base 0x3f000000)
(label! :boot)
(move sp :boot)

; shut down cores 1-3
(move-to-coprocessor {:processor 15
                      :operations [0 5]
                      :source-register (r 5)
                      :dest-registers [(c 0) (c 0)]})

(and (r 5) (r 5) 3)
(cmp (r 5) 0)
(branch {:cond :not-equal} :halt)

;; set r3 to gpio base
(move (r 3) :mmio-base)
(or (r 3) (r 3) 0x200000)

;; set r4 to uart-base
(or (r 4) (r 4) 0x1000)

;; disable uart 0
(or (r 5) (r 4) 0x30)
(store (r 5) 0)

;;; see https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
;;; pages 100 and following

;; disable pull-up/pull down
(or (r 5) (r 3) 0x94)
(store (r 5) 0)
;; delay for 150 cycles
(move (r 0) 150) 
(branch-link :delay)

(label! end)
(branch :end)

(label! delay)
(subtract {:flags true} (r 0) 1)
(branch {:cond :not-equal} #delay)
(branch-exchange lr)