To accelerate sending ACKs, this patch avoids the call setup overhead
of usb_tx and introduces a dedicated inline function. In experiments,
this reduced EOP-to-ACK time by about 10 full-speed bit times.
---
softusb-input/main.c | 15 ++++++++++++---
1 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/softusb-input/main.c b/softusb-input/main.c
index 0318aee..dc6fa26 100644
--- a/softusb-input/main.c
+++ b/softusb-input/main.c
@@ -99,6 +99,16 @@ static void usb_tx(const unsigned char *buf, unsigned char
len)
while(rio8(SIE_TX_BUSY));
}
+static inline void usb_ack(void)
+{
+ wio8(SIE_TX_DATA, 0x80); /* send SYNC */
+ while(rio8(SIE_TX_PENDING));
+ wio8(SIE_TX_DATA, USB_PID_ACK); /* send SYNC */
+ while(rio8(SIE_TX_PENDING));
+ wio8(SIE_TX_VALID, 0);
+ while(rio8(SIE_TX_BUSY));
+}
+
static const char transfer_start[] PROGMEM = "Transfer start: ";
static const char timeout_error[] PROGMEM = "RX timeout error\n";
static const char bitstuff_error[] PROGMEM = "RX bitstuff error\n";
@@ -163,7 +173,6 @@ static int usb_in(unsigned addr, unsigned char
expected_data,
unsigned char *buf, unsigned char maxlen)
{
unsigned char in[3];
- unsigned char ack[1] = { USB_PID_ACK };
unsigned char len = 1;
unsigned char i;
@@ -203,7 +212,7 @@ ignore:
WAIT_RX(0, ignore_eop);
goto complain; /* this doesn't stop - just quit silently */
ignore_eop:
- usb_tx(ack, 1);
+ usb_ack();
complain:
print_string(datax_mismatch);
return 0;
@@ -218,7 +227,7 @@ receive:
buf[len++] = rio8(SIE_RX_DATA);
}
eop:
- usb_tx(ack, 1);
+ usb_ack();
return len;
discard:
--
1.7.1
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