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authorPaul Selkirk <pselkirk@isc.org>2014-09-03 10:07:59 -0400
committerPaul Selkirk <pselkirk@isc.org>2014-09-03 10:07:59 -0400
commita768072bbe3ea9762ee3325ffb5c42c3156e7859 (patch)
tree4ab6d3b54c75a3828c4fc00c6a2e06e0756f8936
parentd846f5ebdec82b4ae21e75e1da02db92f9bcd715 (diff)
fix i2c read buffer overrun
If a client requests data beyond the end of the coretest response, i2c_core could wait forever for txd_syn to be asserted, locking up the system. The current solution is to assume that data will be available by the time the client sends the READ_CMD and then issues the i2c read request; if no data is available, i2c_core returns 0x00. Given the relative speeds of the i2c bus and the FPGA, this seems justifiable, but it could use more scrutiny.
-rw-r--r--src/rtl/i2c_core.v17
1 files changed, 6 insertions, 11 deletions
diff --git a/src/rtl/i2c_core.v b/src/rtl/i2c_core.v
index 3e2772a..a026545 100644
--- a/src/rtl/i2c_core.v
+++ b/src/rtl/i2c_core.v
@@ -175,14 +175,12 @@ module i2c_core (
I2C_nstate = ((SDA_cstate == SDA_FALL) && (SCL_cstate == SCL_HIGH)) ? I2C_RESTART : // repeated start
((I2C_bitcnt > 4'h7) && (SCL_cstate == SCL_FALL)) ? I2C_RXD_SYN : I2C_WR_DATA;
end
- // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
I2C_RXD_SYN: begin // put data on the coretest bus
I2C_nstate = I2C_RXD_ACK;
end
I2C_RXD_ACK: begin // wait for coretest ack
I2C_nstate = rxd_ack ? I2C_ACK_WR : I2C_RXD_ACK;
end
- // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I2C_ACK_WR: begin // trigger the ack response (pull SDA low until next falling edge)
// and stay in this state until the next falling edge of SCL
I2C_nstate = (SCL_cstate == SCL_FALL) ? I2C_END_WR : I2C_ACK_WR;
@@ -192,14 +190,15 @@ module i2c_core (
end
// read branch
- // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
- I2C_TXD_SYN: begin // get data from the coretest bus
- I2C_nstate = txd_syn ? I2C_TXD_ACK : I2C_TXD_SYN;
+ I2C_TXD_SYN: begin // get data from the coretest bus
+ // if data isn't available (txd_syn isn't asserted) by the time we
+ // get to this state, it probably never will be, so skip it
+ I2C_nstate = txd_syn ? I2C_TXD_ACK : I2C_RD_DATA;
end
I2C_TXD_ACK: begin // send coretest ack
+ // hold ack high until syn is lowered
I2C_nstate = txd_syn ? I2C_TXD_ACK : I2C_RD_DATA;
end
- // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I2C_RD_DATA: begin // 8 bits to get the read data
I2C_nstate = ((SDA_cstate == SDA_FALL) && (SCL_cstate == SCL_HIGH)) ? I2C_RESTART : // repeated start
((I2C_bitcnt > 4'h7) && (SCL_cstate == SCL_FALL)) ? I2C_ACK_RD : I2C_RD_DATA;
@@ -300,8 +299,7 @@ module i2c_core (
I2C_daddr <= I2C_daddr;
I2C_rdata <= I2C_rdata;
end // case: I2C_WR_DATA
- // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
- I2C_RXD_SYN: begin // put data on the coretest bus
+ I2C_RXD_SYN: begin // put data on the coretest bus and raise syn
rxd_syn_reg <= 1;
end
I2C_RXD_ACK: begin // wait for coretest ack
@@ -310,7 +308,6 @@ module i2c_core (
rxd_syn_reg <= 0;
end
end
- // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I2C_ACK_WR: begin
SDA_pd <= 1'b1; // active pull down ACK
I2C_daddr <= I2C_daddr;
@@ -327,7 +324,6 @@ module i2c_core (
end
// read branch
- // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
I2C_TXD_SYN: begin // get data from the coretest bus
if (txd_syn)
begin
@@ -341,7 +337,6 @@ module i2c_core (
txd_ack_reg <= 0;
end
end
- // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I2C_RD_DATA: begin // shift out data on falling edges of clock
SDA_pd <= I2C_rdata[7] ? 1'b0 : 1'b1;
if( SCL_cstate == SCL_RISE ) begin