Add PSRAM test case

Firmware/Test Sketches/PSRAM/PSRAM.ino

@@ -0,0 +1,122 @@
+/*
+  Lee Leahy
+  12 June 2023
+
+  Determine the performance of the PSRAM.
+
+  Based upon: https://thingpulse.com/esp32-how-to-use-psram/
+         and: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/external-ram.html
+*/
+
+#include <Arduino.h>
+
+#define MAX_LOOP_COUNT      (1 * 1000 * 1000)
+#define PSRAM_BYTES         (2 * 1024 * 1024)
+
+volatile uint8_t * buffer;
+volatile uint8_t internalRam;
+int psramBytes;
+uint32_t psramPageSize;
+
+void setup()
+{
+    Serial.begin(115200);
+    delay(1000);
+    Serial.println();
+    Serial.println();
+    Serial.print("PSRAM Size: ");
+    Serial.print(ESP.getPsramSize());
+    Serial.println();
+    Serial.println("PSRAM Access Times");
+}
+
+void loop()
+{
+    int32_t index;
+    uint8_t junk;
+    uint32_t loopOverhead;
+    uint32_t microsEnd;
+    uint32_t microsStart;
+    uint32_t offset;
+
+    // Read data from the data cache
+    buffer = (volatile uint8_t *)ps_malloc(PSRAM_BYTES);
+    Serial.print("PSRAM buffer: ");
+    Serial.printf("%p\r\n", buffer);
+    Serial.flush();
+
+    // Compute the loop overhead
+    microsStart = micros();
+    for (index = 0; index < MAX_LOOP_COUNT; index++)
+    {
+    }
+    microsEnd = micros();
+    displayTime(microsStart, microsEnd, 0, "Loop overhead");
+    loopOverhead = microsEnd - microsStart;
+
+    // Prime the data
+    junk = internalRam;
+
+    // Read data from the internal RAM
+    microsStart = micros();
+    for (index = 0; index < MAX_LOOP_COUNT; index++)
+        junk = internalRam;
+    microsEnd = micros();
+    displayTime(microsStart, microsEnd, loopOverhead, "Internal RAM access");
+
+    if (buffer)
+    {
+        // Measure cached PSRAM access
+        microsStart = micros();
+        for (index = 0; index < MAX_LOOP_COUNT; index++)
+            junk = buffer[0];
+        microsEnd = micros();
+        displayTime(microsStart, microsEnd, loopOverhead, "Cached PSRAM access");
+
+        // Separate the two sets of measurements
+        Serial.println();
+
+        // Compute the loop overhead
+        microsStart = micros();
+        for (index = 0; index < MAX_LOOP_COUNT; index++)
+        {
+            junk = buffer[offset];
+            offset = (offset + psramPageSize) & (PSRAM_BYTES - 1);
+        }
+        microsEnd = micros();
+        displayTime(microsStart, microsEnd, 0, "Loop overhead");
+        loopOverhead = microsEnd - microsStart;
+
+        // Measure sequential accesses to PSRAM
+        for (psramPageSize = 1; psramPageSize <= 4096; psramPageSize <<= 1)
+        {
+            microsStart = micros();
+            for (index = 0; index < MAX_LOOP_COUNT; index++)
+            {
+                junk = buffer[offset];
+                offset = (offset + psramPageSize) & (PSRAM_BYTES - 1);
+            }
+            microsEnd = micros();
+            sprintf((char *)buffer, "Uncached PSRAM access, %4d byte page size", psramPageSize);
+            displayTime(microsStart, microsEnd, loopOverhead, (const char *)buffer);
+        }
+    }
+
+    // Done
+    while (1);
+}
+
+void displayTime(uint32_t microsStart, uint32_t microsEnd, uint32_t loopOverhead, const char * string)
+{
+    uint32_t delta;
+    float nanoSeconds;
+    char text[128];
+
+    // Display the cache read time
+    delta = microsEnd - microsStart - loopOverhead;
+    nanoSeconds = (double)delta / 1000.;
+    sprintf(text, "%s: %8d - %8d - %5d = %7d: %7.3f nSec",
+            string, microsEnd, microsStart, loopOverhead, delta, nanoSeconds);
+    Serial.println(text);
+    Serial.flush();
+}