Properly map IO and PAD register offsets for QSPI

In the UART bootloader example the QSPI pins are used for normal IO and
a `qspi_gpio_set_function()` function is used locally to setup the pins.
This function didn't take into account that the IO and PAD register
banks for the QSPI IOs are not in the same order. We correct this by
adding a lookup table to map between the two.

Author: lifeisafractal

bootloaders/uart/uart_binary.c

@@ -14,7 +14,7 @@
 #endif
 
 // Initialize the GPIO for the LED
-void pico_led_init(void) {
+static void pico_led_init(void) {
 #ifdef PICO_DEFAULT_LED_PIN
     // A device like Pico that uses a GPIO for the LED will define PICO_DEFAULT_LED_PIN
     // so we can use normal GPIO functionality to turn the led on and off
@@ -24,23 +24,44 @@ void pico_led_init(void) {
 }
 
 // Turn the LED on or off
-void pico_set_led(bool led_on) {
+static void pico_set_led(bool led_on) {
 #if defined(PICO_DEFAULT_LED_PIN)
     // Just set the GPIO on or off
     gpio_put(PICO_DEFAULT_LED_PIN, led_on);
 #endif
 }
 
+enum qspi_gpio {
+    // arbitrarily choose PAD register bank to set the order
+    QSPI_GPIO_SCLK = 0,
+    QSPI_GPIO_SD0 = 1,
+    QSPI_GPIO_SD1 = 2,
+    QSPI_GPIO_SD2 = 3,
+    QSPI_GPIO_SD3 = 4,
+    QSPI_GPIO_SS = 5,
+};
+
+// curiously the IO and PAD register banks for the QSPI GPIOs are not in the same order
+// This look up table will map the PAD offset to the IO offset for the same pin
+static const uint QSPI_GPIO_PAD_TO_IO_OFFSET[] = {
+    0, // SCLK
+    2, // SD0
+    3, // SD1
+    4, // SD2
+    5, // SD3
+    1, // SS 
+};
+
 // Set function for QSPI GPIO pin
-void qspi_gpio_set_function(uint gpio, gpio_function_t fn) {
+static void qspi_gpio_set_function(enum qspi_gpio gpio, gpio_function_t fn) {
     // Set input enable on, output disable off
     hw_write_masked(&pads_qspi_hw->io[gpio],
                    PADS_QSPI_GPIO_QSPI_SD2_IE_BITS,
                    PADS_QSPI_GPIO_QSPI_SD2_IE_BITS | PADS_QSPI_GPIO_QSPI_SD2_OD_BITS
     );
     // Zero all fields apart from fsel; we want this IO to do what the peripheral tells it.
     // This doesn't affect e.g. pullup/pulldown, as these are in pad controls.
-    io_qspi_hw->io[gpio].ctrl = fn << IO_QSPI_GPIO_QSPI_SD2_CTRL_FUNCSEL_LSB;
+    io_qspi_hw->io[QSPI_GPIO_PAD_TO_IO_OFFSET[gpio]].ctrl = fn << IO_QSPI_GPIO_QSPI_SD2_CTRL_FUNCSEL_LSB;
 
     // Remove pad isolation now that the correct peripheral is in control of the pad
     hw_clear_bits(&pads_qspi_hw->io[gpio], PADS_QSPI_GPIO_QSPI_SD2_ISO_BITS);
@@ -49,9 +70,9 @@ void qspi_gpio_set_function(uint gpio, gpio_function_t fn) {
 int main() {
     pico_led_init();
 
-    // SD2 is QSPI GPIO 3, SD3 is QSPI GPIO 4
-    qspi_gpio_set_function(3, GPIO_FUNC_UART_AUX);
-    qspi_gpio_set_function(4, GPIO_FUNC_UART_AUX);
+    // SD2 is UART0 TX, SD3 is UART0 RX (same as the ROM UART bootloader)
+    qspi_gpio_set_function(QSPI_GPIO_SD2, GPIO_FUNC_UART_AUX);
+    qspi_gpio_set_function(QSPI_GPIO_SD3, GPIO_FUNC_UART_AUX);
 
     uart_init(uart0, 1000000);