Display POST codes during IPL on Arctic Tern alphanumeric display instead of dot points

kestrel/src/kestrel.c

-// © 2020 - 2021 Raptor Engineering, LLC
+// © 2020 - 2022 Raptor Engineering, LLC
 //
 // Released under the terms of the GPL v3
 // See the LICENSE file for full details
@@ -358,8 +358,11 @@ static void display_character(char character, int dp)
     // Switch display into alphanumeric mode
     gpio1_out_write(gpio1_out_read() | (0x1 << 18));
 
-    // Write character
-    gpio2_out_write((gpio2_out_read() & ~0xff) | (character & 0xff));
+    if (host_power_status != HOST_POWER_STATUS_IPLING)
+    {
+        // Write character
+        gpio2_out_write((gpio2_out_read() & ~0xff) | (character & 0xff));
+    }
 }
 
 static void host_power_status_changed(void)
@@ -391,6 +394,47 @@ static void set_led_bank_display(uint8_t bitfield)
     gpio1_out_write((gpio1_out_read() & ~0xf) | (bitfield & 0xf));
 }
 
+static void set_led_post_code_alphanumeric_display(uint16_t value)
+{
+    uint32_t dword;
+
+    // Convert POST code to string
+    unsigned char post_code_string[5];
+    snprintf(post_code_string, 5, "%02d%02d", (value >> 8) & 0xff, value & 0xff);
+
+    if ((host_power_status == HOST_POWER_STATUS_IPLING) && (value != 0x0))
+    {
+        // Display value on the alphanumeric LED display
+        dword = gpio2_out_read();
+        dword &= ~0xffffffff;
+        dword |= post_code_string[0] << 24;
+        dword |= post_code_string[1] << 16;
+        dword |= post_code_string[2] << 8;
+        dword |= post_code_string[3];
+        gpio2_out_write(dword);
+
+        // Set decimal point
+        gpio1_out_write((gpio1_out_read() & ~0xf) | 0x2);
+    }
+    else
+    {
+        // Clear middle two segments when IPL is not in progress
+        dword = gpio2_out_read();
+        dword &= ~0xffffffff;
+        dword |= (' ' << 24) | (' ' << 16) | (' ' << 8) | ' ';
+        gpio2_out_write(dword);
+
+        // Clear decimal point
+       gpio1_out_write(gpio1_out_read() & ~0xf);
+
+        // Ensure upper power status character is rewritten
+        host_power_status_changed();
+
+        // Ensure lower host status character is rewritten
+        display_character('0' + 2 + host_power_status, 0); // STATUS CODE
+    }
+}
+
 static void display_post_code(uint16_t post_code)
 {
     uint8_t host_status_led_post_code;
@@ -401,12 +445,14 @@ static void display_post_code(uint16_t post_code)
     {
         // IPL complete!
         set_led_bank_display(0);
+        set_led_post_code_alphanumeric_display(0);
         i2c_write_register_byte((uint8_t *)P9PS_I2C_MASTER_BASE_ADDR, HOST_PLATFORM_FPGA_I2C_ADDRESS, HOST_PLATFORM_FPGA_I2C_REG_STA_LED, 0x00);
     }
     else if (post_code == 0x0)
     {
         // System offline
         set_led_bank_display(0);
+        set_led_post_code_alphanumeric_display(0);
         i2c_write_register_byte((uint8_t *)P9PS_I2C_MASTER_BASE_ADDR, HOST_PLATFORM_FPGA_I2C_ADDRESS, HOST_PLATFORM_FPGA_I2C_REG_STA_LED, 0x00);
     }
     else {
@@ -440,7 +486,15 @@ static void display_post_code(uint16_t post_code)
             default: host_status_led_post_code = 0;
         }
 
-        set_led_bank_display(led_post_code);
+        // Only one way to display the POST codes is strictly necessary...
+        if (0)
+        {
+            set_led_bank_display(led_post_code);
+        }
+        else
+        {
+            set_led_post_code_alphanumeric_display(post_code);
+        }
         i2c_write_register_byte((uint8_t *)P9PS_I2C_MASTER_BASE_ADDR, HOST_PLATFORM_FPGA_I2C_ADDRESS, HOST_PLATFORM_FPGA_I2C_REG_STA_LED, 0x80 | host_status_led_post_code);
     }
 }