From: Gerhard Sittig <redacted>
Date: Sat, 9 May 2020 16:28:02 +0000 (+0200)
Subject: asix-sigma: rephrase some of the FPGA command exchange
X-Git-Url: https://sigrok.org/gitweb/?p=libsigrok.git;a=commitdiff_plain;h=07411a605ed83f7a57db9d805731c0abe5893df7

asix-sigma: rephrase some of the FPGA command exchange

Eliminate a few magic numbers in FPGA commands, use symbolic identifiers
for automatic register address increments, and DRAM access bank selects.
Improve grouping of related declarations in the header file.
---

diff --git a/src/hardware/asix-sigma/protocol.c b/src/hardware/asix-sigma/protocol.c
index 0e27f07a..c4012d78 100644
--- a/src/hardware/asix-sigma/protocol.c
+++ b/src/hardware/asix-sigma/protocol.c
@@ -134,15 +134,18 @@ static int sigma_read_register(uint8_t reg, uint8_t *data, size_t len,
 static int sigma_read_pos(uint32_t *stoppos, uint32_t *triggerpos,
 			  struct dev_context *devc)
 {
+	/*
+	 * Read 6 registers starting at trigger position LSB.
+	 * Which yields two 24bit counter values.
+	 */
 	uint8_t buf[] = {
 		REG_ADDR_LOW | READ_TRIGGER_POS_LOW,
-
-		REG_READ_ADDR | NEXT_REG,
-		REG_READ_ADDR | NEXT_REG,
-		REG_READ_ADDR | NEXT_REG,
-		REG_READ_ADDR | NEXT_REG,
-		REG_READ_ADDR | NEXT_REG,
-		REG_READ_ADDR | NEXT_REG,
+		REG_READ_ADDR | REG_ADDR_INC,
+		REG_READ_ADDR | REG_ADDR_INC,
+		REG_READ_ADDR | REG_ADDR_INC,
+		REG_READ_ADDR | REG_ADDR_INC,
+		REG_READ_ADDR | REG_ADDR_INC,
+		REG_READ_ADDR | REG_ADDR_INC,
 	};
 	uint8_t result[6];
 
@@ -172,32 +175,35 @@ static int sigma_read_pos(uint32_t *stoppos, uint32_t *triggerpos,
 static int sigma_read_dram(uint16_t startchunk, size_t numchunks,
 			   uint8_t *data, struct dev_context *devc)
 {
-	size_t i;
 	uint8_t buf[4096];
 	int idx;
+	size_t chunk;
+	int sel;
+	gboolean is_last;
 
-	/* Send the startchunk. Index start with 1. */
+	/* Communicate DRAM start address (memory row, aka samples line). */
 	idx = 0;
 	buf[idx++] = startchunk >> 8;
 	buf[idx++] = startchunk & 0xff;
 	sigma_write_register(WRITE_MEMROW, buf, idx, devc);
 
-	/* Read the DRAM. */
+	/*
+	 * Access DRAM content. Fetch from DRAM to FPGA's internal RAM,
+	 * then transfer via USB. Interleave the FPGA's DRAM access and
+	 * USB transfer, use alternating buffers (0/1) in the process.
+	 */
 	idx = 0;
 	buf[idx++] = REG_DRAM_BLOCK;
 	buf[idx++] = REG_DRAM_WAIT_ACK;
-
-	for (i = 0; i < numchunks; i++) {
-		/* Alternate bit to copy from DRAM to cache. */
-		if (i != (numchunks - 1))
-			buf[idx++] = REG_DRAM_BLOCK | (((i + 1) % 2) << 4);
-
-		buf[idx++] = REG_DRAM_BLOCK_DATA | ((i % 2) << 4);
-
-		if (i != (numchunks - 1))
+	for (chunk = 0; chunk < numchunks; chunk++) {
+		sel = chunk % 2;
+		is_last = chunk == numchunks - 1;
+		if (!is_last)
+			buf[idx++] = REG_DRAM_BLOCK | REG_DRAM_SEL_BOOL(!sel);
+		buf[idx++] = REG_DRAM_BLOCK_DATA | REG_DRAM_SEL_BOOL(sel);
+		if (!is_last)
 			buf[idx++] = REG_DRAM_WAIT_ACK;
 	}
-
 	sigma_write(buf, idx, devc);
 
 	return sigma_read(data, numchunks * CHUNK_SIZE, devc);
diff --git a/src/hardware/asix-sigma/protocol.h b/src/hardware/asix-sigma/protocol.h
index a32ee15e..edace1e5 100644
--- a/src/hardware/asix-sigma/protocol.h
+++ b/src/hardware/asix-sigma/protocol.h
@@ -85,22 +85,34 @@ enum sigma_read_register {
 	READ_TEST		= 15,
 };
 
+/*
+ * FPGA commands are 8bits wide. The upper nibble is a command opcode,
+ * the lower nibble can carry operand values. 8bit register addresses
+ * and 8bit data values get communicated in two steps.
+ */
+
+/* Register access. */
 #define REG_ADDR_LOW		(0x0 << 4)
 #define REG_ADDR_HIGH		(0x1 << 4)
 #define REG_DATA_LOW		(0x2 << 4)
 #define REG_DATA_HIGH_WRITE	(0x3 << 4)
 #define REG_READ_ADDR		(0x4 << 4)
-#define REG_DRAM_WAIT_ACK	(0x5 << 4)
-
-/* Bit (1 << 4) can be low or high (double buffer / cache) */
-#define REG_DRAM_BLOCK		(0x6 << 4)
-#define REG_DRAM_BLOCK_BEGIN	(0x8 << 4)
-#define REG_DRAM_BLOCK_DATA	(0xa << 4)
+#define REG_ADDR_ADJUST		(1 << 0) /* Auto adjust register address. */
+#define REG_ADDR_DOWN		(1 << 1) /* 1 decrement, 0 increment. */
+#define REG_ADDR_INC		(REG_ADDR_ADJUST)
+#define REG_ADDR_DEC		(REG_ADDR_ADJUST | REG_ADDR_DOWN)
+
+/* Sample memory access. */
+#define REG_DRAM_WAIT_ACK	(0x5 << 4) /* Wait for completion. */
+#define REG_DRAM_BLOCK		(0x6 << 4) /* DRAM to BRAM, plus bank select. */
+#define REG_DRAM_BLOCK_BEGIN	(0x8 << 4) /* Read first BRAM bytes. */
+#define REG_DRAM_BLOCK_DATA	(0xa << 4) /* Read full BRAM block. */
+#define REG_DRAM_SEL_N		(0x1 << 4) /* Bank select, added to 6/8/a. */
+#define REG_DRAM_SEL_BOOL(b)	((b) ? REG_DRAM_SEL_N : 0)
 
 #define LEDSEL0			6
 #define LEDSEL1			7
 
-#define NEXT_REG		1
 
 #define EVENTS_PER_CLUSTER	7