[flashrom] [PATCH] ch341a_spi: provide nACT/ACT with CS1/2 for ISP use

[Urja Rannikko]

This allows to drive MCU RST lines or similar with the ch341a
during a flashrom run. CS1 is active low and CS2 is active high;
note that the tristate state is a weak pullup, thus using
CS2 would need an external pull-down.

Signed-off-by: Urja Rannikko <urjaman at gmail.com>
---
 ch341a_spi.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/ch341a_spi.c b/ch341a_spi.c
index 6eb2804..80717f8 100644
--- a/ch341a_spi.c
+++ b/ch341a_spi.c
@@ -288,10 +288,10 @@ static uint8_t swap_byte(uint8_t x)
 }
 
 /* The assumed map between UIO command bits, pins on CH341A chip and pins on SPI chip:
- * UIO	CH341A	SPI	CH341A SPI name
+ * UIO	CH341A	SPI	CH341A SPI name		Comment
  * 0	D0/15	CS/1 	(CS0)
- * 1	D1/16	unused	(CS1)
- * 2	D2/17	unused	(CS2)
+ * 1	D1/16	unused	(CS1)			nACT, drives low when flashrom active
+ * 2	D2/17	unused	(CS2)			ACT, drives high when flashrom active
  * 3	D3/18	SCK/6	(DCK)
  * 4	D4/19	unused	(DOUT2)
  * 5	D5/20	SI/5	(DOUT)
@@ -299,12 +299,15 @@ static uint8_t swap_byte(uint8_t x)
  *  mapped as follows:
  *	D6/21	unused	(DIN2)
  *	D7/22	SO/2	(DIN)
+ * CS1 and CS2 are driven nACT & ACT as a bonus by flashrom for ISP uses to drive a
+ * reset signal or similar. Note that the tristate state is a weak pullup, so using
+ * CS2 would need an external pull-down.
  */
 static int32_t enable_pins(bool enable)
 {
 	uint8_t buf[] = {
 		CH341A_CMD_UIO_STREAM,
-		CH341A_CMD_UIO_STM_OUT | 0x37, // CS high (all of them), SCK=0, DOUT*=1
+		CH341A_CMD_UIO_STM_OUT | (enable ? 0x35 : 0x33), // SCK=0, DOUT*=1, CS*= see above
 		CH341A_CMD_UIO_STM_DIR | (enable ? 0x3F : 0x00), // Interface output enable / disable
 		CH341A_CMD_UIO_STM_END,
 	};
@@ -327,11 +330,11 @@ static void pluck_cs(uint8_t *ptr)
 		stored_delay_us = 0;
 	}
 	*ptr++ = CH341A_CMD_UIO_STREAM;
-	*ptr++ = CH341A_CMD_UIO_STM_OUT | 0x37; /* deasserted */
+	*ptr++ = CH341A_CMD_UIO_STM_OUT | 0x35; /* deasserted */
 	int i;
 	for (i = 0; i < delay_cnt; i++)
-		*ptr++ = CH341A_CMD_UIO_STM_OUT | 0x37; /* "delay" */
-	*ptr++ = CH341A_CMD_UIO_STM_OUT | 0x36; /* asserted */
+		*ptr++ = CH341A_CMD_UIO_STM_OUT | 0x35; /* "delay" */
+	*ptr++ = CH341A_CMD_UIO_STM_OUT | 0x34; /* asserted */
 	*ptr++ = CH341A_CMD_UIO_STM_END;
 }
 
-- 
2.7.1