diff options
Diffstat (limited to 'blink.s')
| -rw-r--r-- | blink.s | 54 |
1 files changed, 14 insertions, 40 deletions
@@ -2,10 +2,6 @@ .cpu cortex-m0plus .thumb -.equ RESETS_BASE, 0x4000c000 -.equ RESET_OFST, 0x0 -.equ RESET_DONE_OFST, 0x8 - .equ IO_BANK0_BASE, 0x40014000 .equ GPIO25_STATUS, (IO_BANK0_BASE + 0x0c8) .equ GPIO25_CTRL, (IO_BANK0_BASE + 0x0cc) @@ -16,43 +12,21 @@ .equ ATOMIC_CLEAR, 0x3000 -.type main, %function -.global main -main: - - // Deassert GPIO reset - ldr r1, =(RESETS_BASE + ATOMIC_CLEAR) - movs r0, 0x20 // IO_BANK0 is bit 5 - str r0, [r1, RESET_OFST] - - // Wait for GPIO reset to finish - ldr r1, =RESETS_BASE -1: - ldr r2, [r1, RESET_DONE_OFST] - tst r0, r2 - beq 1b +.type blink, %function +.global blink - // Set GPIO25 function to SIO +blink: ldr r1, =GPIO25_CTRL - movs r0, #5 - str r0, [r1, #0] - + movs r0, 5 // SIO function = 5 + str r0, [r1, 0] ldr r1, =SIO_BASE - - // Set output enable for GPIO 25 - movs r0, #1 - lsls r0, r0, #25 + movs r0, 1 + lsls r0, r0, 25 // GPIO 25 (LED) output enable str r0, [r1, GPIO_OE_SET_OFST] - -loop: - - // Toggle output level for GPIO 25 - str r0, [r1, GPIO_OUT_XOR_OFST] - - // Delay - ldr r2, =400000 -1: - subs r2, r2, #1 - bne 1b - - b loop +toggle_one_second: + str r0, [r1, GPIO_OUT_XOR_OFST] // toggle GPIO 25 output level + ldr r2, =0x1fca055 // 33.3 * 10^6 (one-third of a second at 100MHz) +1: // 3 clock cycle loop + subs r2, r2, 1 // 1 clock cycle + bne 1b // 2 clock cycles when taken + b toggle_one_second |