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0x0008_uninitialized-variables-e/0x0008_uninitialized-variables-e.c

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+/**
+ * @file 0x0008_uninitialized-variables-e.c
+ * @brief Blink LED using pure inline ARM assembly with direct register addresses
+ * @author Kevin Thomas
+ * @date 2025
+ *
+ * MIT License
+ *
+ * Copyright (c) 2025 Kevin Thomas
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * -----------------------------------------------------------------------------
+ *
+ * Blinks an LED on GPIO16 using pure inline ARM assembly. No SDK calls, no
+ * includes. Configures PADS_BANK0, IO_BANK0, and GPIO coprocessor via direct
+ * register addresses and mcrr instructions, with a busy-wait delay loop.
+ *
+ * Wiring:
+ *   GPIO16 -> LED anode (with current-limiting resistor to GND)
+ */
+
+int main(void) {
+    __asm__ volatile (
+        //   gpio_init(LED_PIN);
+        ///  gpio_set_dir(LED_PIN, GPIO_IN);
+        //// gpioc_bit_oe_put(LED_PIN, GPIO_OUT);
+        "movs r4, #0x10\n"                  // GPIO16
+        "movs r5, #0x01\n"                  // bit 1; used for OUT/OE writes
+        "mcrr p0, #4, r4, r5, c4\n"         // gpioc_bit_oe_put(16, 1); p102
+
+        //   gpio_set_function(LED_PIN, GPIO_FUNC_SIO);
+        ///  hw_write_masked(&pads_bank0_hw->io[LED_PIN],
+        ///                  PADS_BANK0_GPIO0_IE_BITS,
+        ///                  PADS_BANK0_GPIO0_IE_BITS | PADS_BANK0_GPIO0_OD_BITS
+        ///  );
+        //// hw_xor_bits(addr, (*addr ^ values) & write_mask);
+        "ldr r3, =0x40038044\n"             // &pads_bank0_hw->io[16]; p785, p796
+        "ldr r2, [r3]\n"                    // load current config  
+        "bic r2, r2, #0x80\n"               // clear OD; output disable
+        "orr r2, r2, #0x40\n"               // set IE; enable input buffer
+        "str r2, [r3]\n"                    // store updated config  
+        ///  io_bank0_hw->io[LED_PIN].ctrl = GPIO_FUNC_SIO << IO_BANK0_GPIO0_CTRL_FUNCSEL_LSB;
+        "ldr r3, =0x40028084\n"             // &io_bank0_hw->io[16].ctrl; p603, p637
+        "ldr r2, [r3]\n"                    // load current config 
+        "bic r2, r2, #0x1f\n"               // clear FUNCSEL bits [4:0]
+        "orr r2, r2, #5\n"                  // set FUNCSEL = 5 (SIO)
+        "str r2, [r3]\n"                    // store updated config
+        ///  hw_clear_bits(&pads_bank0_hw->io[gpio], PADS_BANK0_GPIO0_ISO_BITS);
+        "ldr r3, =0x40038044\n"             // &pads_bank0_hw->io[16]; p785, p796
+        "ldr r2, [r3]\n"                    // load current config  
+        "bic r2, r2, #0x100\n"              // clear ISO bit (bit 8) un‑isolate pad  
+        "str r2, [r3]\n"                    // store updated config  
+
+        //   gpio_set_dir(LED_PIN, GPIO_OUT);
+        ///  gpioc_bit_oe_put(LED_PIN, GPIO_OUT);
+        "movs r4, #0x10\n"                  // GPIO16
+        "movs r5, #0x01\n"                  // bit 1; used for OUT/OE writes
+        "mcrr p0, #4, r4, r5, c4\n"         // gpioc_bit_oe_put(16, 1); p102   
+
+        //   while (true)
+        "1:\n"                              // loop start  
+
+        //   gpio_put(LED_PIN, 1);
+        ///  gpioc_bit_out_put(LED_PIN, 1);
+        "movs r4, #0x10\n"                  // GPIO16
+        "movs r5, #0x01\n"                  // bit 1; used for OUT/OE writes
+        "mcrr p0, #4, r4, r5, c0\n"         // gpioc_bit_out_put(16, 1) 
+        //   sleep_ms(500);
+        ///  sleep_us(500 * 1000ull);
+        "ldr r2, =0x17D7840\n"              // r2 = ~8.4M cycles  
+        "2:\n"                              // delay loop  
+        "subs r2, r2, #1\n"                 // decrement counter  
+        "bne 2b\n"                          // repeat until zero 
+        
+        //   gpio_put(LED_PIN, 1);
+        ///  gpioc_bit_out_put(LED_PIN, 1);
+        "movs r4, #0x10\n"                  // GPIO16
+        "movs r5, #0x00\n"                  // bit 0; used for OUT/OE writes
+        "mcrr p0, #4, r4, r5, c0\n"         // gpioc_bit_out_put(16, 0) 
+        //   sleep_ms(500);
+        ///  sleep_us(500 * 1000ull);
+        "ldr r2, =0x17D7840\n"              // r2 = ~8.4M cycles 
+        "3:\n"                              // delay loop  
+        "subs r2, r2, #1\n"                 // decrement counter 
+        "bne 3b\n"                          // repeat until zero
+
+        //    jmp
+        "b 1b\n"                            // repeat forever  
+    );  
+}