drivers/swd: add support for SWD multidrop

According to ARM IHI0031C+ chapter 2.3.11 "TARGETSEL, Target Selection register"
multidrop capable DPv2 must not drive SWDIO line during the response phase
of a write to TARGETSEL register.

Introduce helper functions swd_cmd_returns_ack() and swd_ack_to_error_code()
to centralize these tests from all drivers to one place.

Introduce distinct error codes for SWD protocol.

Partly inspired by Graham Sanderson's http://review.openocd.org/4935

Change-Id: Ie5f9edb22e066a933a534bf2b29e7e1d3087dad1
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/6699
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins

1 files changed, 41 insertions, 0 deletions

diff --git a/src/jtag/swd.h b/src/jtag/swd.h
index fe28667..8a436d0 100644
--- a/src/jtag/swd.h
+++ b/src/jtag/swd.h
@@ -18,6 +18,7 @@
 #ifndef OPENOCD_JTAG_SWD_H
 #define OPENOCD_JTAG_SWD_H
 
+#include <helper/log.h>
 #include <target/arm_adi_v5.h>
 
 /* Bits in SWD command packets, written from host to target
@@ -32,6 +33,12 @@
 #define SWD_CMD_PARK	(1 << 7)	/* driven high by host */
 /* followed by TRN, 3-bits of ACK, TRN */
 
+/*
+ * The SWD subsystem error codes
+ */
+#define ERROR_SWD_FAIL	(-400)	/** protocol or parity error */
+#define ERROR_SWD_FAULT	(-401)	/** device returned FAULT in ACK field */
+
 /**
  * Construct a "cmd" byte, in lSB bit order, which swd_driver.read_reg()
  * and swd_driver.write_reg() methods will use directly.
@@ -53,6 +60,40 @@ static inline uint8_t swd_cmd(bool is_read, bool is_ap, uint8_t regnum)
 
 /* SWD_ACK_* bits are defined in <target/arm_adi_v5.h> */
 
+/**
+ * Test if we can rely on ACK returned by SWD command
+ *
+ * @param cmd Byte constructed by swd_cmd(), START, STOP and TRN are filtered off
+ * @returns true if ACK should be checked, false if should be ignored
+ */
+static inline bool swd_cmd_returns_ack(uint8_t cmd)
+{
+	uint8_t base_cmd = cmd & (SWD_CMD_APNDP | SWD_CMD_RNW | SWD_CMD_A32);
+
+	/* DPv2 does not reply to DP_TARGETSEL write cmd */
+	return base_cmd != swd_cmd(false, false, DP_TARGETSEL);
+}
+
+/**
+ * Convert SWD ACK value returned from DP to OpenOCD error code
+ *
+ * @param ack
+ * @returns error code
+ */
+static inline int swd_ack_to_error_code(uint8_t ack)
+{
+	switch (ack) {
+	case SWD_ACK_OK:
+		return ERROR_OK;
+	case SWD_ACK_WAIT:
+		return ERROR_WAIT;
+	case SWD_ACK_FAULT:
+		return ERROR_SWD_FAULT;
+	default:
+		return ERROR_SWD_FAIL;
+	}
+}
+
 /*
  * The following sequences are updated to
  * ARM(tm) Debug Interface v5 Architecture Specification    ARM IHI 0031E