Keyborg: encode the scanned heat map to fit into RAM

A single frame of the scanned heat map is too big to fit into RAM. Let's
encode it so that we can get the whole frame.

BUG=None
TEST=Touch on various places on the panel and see corresponding results.
BRANCH=None

Change-Id: I8c7c72d5d4a83ebc2018c0abd57075697c931bef
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/199940
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

4 files changed, 143 insertions, 22 deletions

diff --git a/board/keyborg/build.mk b/board/keyborg/build.mk
index b31dafce38..cdd1a7ff84 100644
--- a/board/keyborg/build.mk
+++ b/board/keyborg/build.mk
@@ -10,4 +10,5 @@ CHIP_FAMILY:=stm32f
 CHIP_VARIANT:=stm32ts60
 
 board-y=board.o hardware.o runtime.o master_slave.o spi_comm.o touch_scan.o
+board-y+=encode.o
 board-$(CONFIG_DEBUG_PRINTF)+=debug.o
diff --git a/board/keyborg/encode.c b/board/keyborg/encode.c
new file mode 100644
index 0000000000..266f67d3b3
--- /dev/null
+++ b/board/keyborg/encode.c
@@ -0,0 +1,114 @@
+/* Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Touch data encoding/decoding */
+
+/*
+ * This removes the "whitespace" (i.e. cells below the threshold) and
+ * group the remaining active cells into "segments". By only storing
+ * the segments, we can fit a single frame in RAM in most cases.
+ */
+
+#include "common.h"
+#include "debug.h"
+#include "touch_scan.h"
+#include "util.h"
+
+#define BUF_SIZE 6000
+static uint8_t encoded[BUF_SIZE];
+static int encoded_size;
+
+void encode_reset(void)
+{
+	/* Just clear the encoded data */
+	encoded_size = 0;
+}
+
+void encode_add_column(const uint8_t *dptr)
+{
+	uint8_t *seg_count_ptr;
+	int p, p_start;
+	uint8_t *eptr = encoded + encoded_size, *e_seg_size;
+
+	seg_count_ptr = eptr;
+	eptr++;
+
+	*seg_count_ptr = 0;
+	p = 0;
+	while (p < ROW_COUNT * 2) {
+		if (dptr[p] < THRESHOLD) {
+			++p;
+			continue;
+		}
+
+		/* Give up on overflow */
+		if (eptr + 2 >= encoded + BUF_SIZE)
+			return;
+
+		/* Save current position */
+		*(eptr++) = p;
+
+		/* Leave a byte for storing segment size */
+		e_seg_size = eptr;
+		eptr++;
+
+		/* Record segment starting point */
+		p_start = p;
+
+		/* Save the segment */
+		while (p < ROW_COUNT * 2 && dptr[p] >= THRESHOLD) {
+			if (eptr >= encoded + BUF_SIZE)
+				return;
+			*(eptr++) = dptr[p++];
+		}
+
+		/* Fill in the segment size now that we know it */
+		*e_seg_size = p - p_start;
+
+		(*seg_count_ptr)++;
+	}
+
+	/* Update encoded data size now that we're sure it fits */
+	encoded_size = eptr - encoded;
+}
+
+void encode_dump_matrix(void)
+{
+	uint8_t *dptr;
+	int row, col;
+	int seg_count;
+	int seg;
+	int seg_end;
+
+	debug_printf("Encoded size = %d\n", encoded_size);
+
+	dptr = encoded;
+	for (col = 0; col < COL_COUNT * 2; ++col) {
+		if (dptr >= encoded + encoded_size) {
+			for (row = 0; row < ROW_COUNT * 2; ++row)
+				debug_printf("  - ");
+			debug_printf("\n");
+			continue;
+		}
+		seg_count = *(dptr++);
+		row = 0;
+		for (seg = 0; seg < seg_count; ++seg) {
+			while (row < *dptr) {
+				debug_printf("  - ");
+				row++;
+			}
+			dptr++;
+			seg_end = *dptr + row;
+			dptr++;
+			for (; row < seg_end; ++row, ++dptr)
+				debug_printf("%3d ", *dptr);
+		}
+		while (row < ROW_COUNT * 2) {
+			debug_printf("  - ");
+			row++;
+		}
+		debug_printf("\n");
+	}
+}
diff --git a/board/keyborg/encode.h b/board/keyborg/encode.h
new file mode 100644
index 0000000000..b743c388d4
--- /dev/null
+++ b/board/keyborg/encode.h
@@ -0,0 +1,20 @@
+/* Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Touch data encoding/decoding */
+
+#ifndef __KEYBORG_ENCODE_H
+#define __KEYBORG_ENCODE_H
+
+/* Start encoding a new frame */
+void encode_reset(void);
+
+/* Encode a single column */
+void encode_add_column(const uint8_t *dptr);
+
+/* Decode and print the encoded frame to console */
+void encode_dump_matrix(void);
+
+#endif  /* __KEYBORG_ENCODE_H */
diff --git a/board/keyborg/touch_scan.c b/board/keyborg/touch_scan.c
index 0728595c5a..9ea947eb43 100644
--- a/board/keyborg/touch_scan.c
+++ b/board/keyborg/touch_scan.c
@@ -9,6 +9,7 @@
 #include "console.h"
 #include "debug.h"
 #include "dma.h"
+#include "encode.h"
 #include "gpio.h"
 #include "hooks.h"
 #include "master_slave.h"
@@ -21,13 +22,7 @@
 #define TS_PIN_TO_CR(p) ((((p).port_id + 1) << 16) | (1 << (p).pin))
 #define TS_GPIO_TO_BASE(p) (0x40010800 + (p) * 0x400)
 
-/*
- * Storage for partial touch scan data. This will be smaller once
- * we figure out how to encode it.
- */
-static uint8_t touch_data[COL_COUNT + 10][ROW_COUNT * 2];
-
-static uint8_t buf[ROW_COUNT * 2];
+static uint8_t buf[2][ROW_COUNT * 2];
 
 static uint32_t mccr_list[COL_COUNT];
 static uint32_t mrcr_list[ROW_COUNT];
@@ -188,7 +183,7 @@ int touch_scan_full_matrix(void)
 {
 	struct spi_comm_packet cmd;
 	const struct spi_comm_packet *resp;
-	int col, row;
+	int col;
 	timestamp_t st = get_time();
 	uint8_t *dptr = NULL, *last_dptr = NULL;
 
@@ -198,6 +193,7 @@ int touch_scan_full_matrix(void)
 	if (spi_master_send_command(&cmd))
 		return EC_ERROR_UNKNOWN;
 
+	encode_reset();
 	for (col = 0; col < COL_COUNT * 2; ++col) {
 		if (col >= COL_COUNT) {
 			enable_col(col - COL_COUNT, 1);
@@ -208,10 +204,7 @@ int touch_scan_full_matrix(void)
 			return EC_ERROR_UNKNOWN;
 
 		last_dptr = dptr;
-		if (col < COL_COUNT + 10)
-			dptr = touch_data[col];
-		else
-			dptr = buf;
+		dptr = buf[col & 1];
 
 		scan_column(dptr + ROW_COUNT);
 
@@ -223,6 +216,7 @@ int touch_scan_full_matrix(void)
 			memcpy(last_dptr, resp->data, resp->size);
 			memset(last_dptr + resp->size, 0,
 					ROW_COUNT - resp->size);
+			encode_add_column(last_dptr);
 		}
 
 		if (master_slave_sync(20) != EC_SUCCESS)
@@ -243,20 +237,12 @@ int touch_scan_full_matrix(void)
 		return EC_ERROR_UNKNOWN;
 	memcpy(last_dptr, resp->data, resp->size);
 	memset(last_dptr + resp->size, 0, ROW_COUNT - resp->size);
+	encode_add_column(last_dptr);
 
 	master_slave_sync(20);
 
 	debug_printf("Sampling took %d us\n", get_time().val - st.val);
-
-	for (row = 0; row < ROW_COUNT * 2; ++row) {
-		for (col = 0; col < COL_COUNT + 10; ++col) {
-			if (touch_data[col][row] < THRESHOLD)
-				debug_printf("  - ");
-			else
-				debug_printf("%3d ", touch_data[col][row]);
-		}
-		debug_printf("\n");
-	}
+	encode_dump_matrix();
 
 	return EC_SUCCESS;
 }